diff --git a/piker/brokers/kraken.py b/piker/brokers/kraken.py
index 30e57b9e..670eed6f 100644
--- a/piker/brokers/kraken.py
+++ b/piker/brokers/kraken.py
@@ -21,6 +21,7 @@ Kraken backend.
 from contextlib import asynccontextmanager as acm
 from dataclasses import asdict, field
 from datetime import datetime
+from pprint import pformat
 from typing import Any, Optional, AsyncIterator, Callable, Union
 import time
 
@@ -569,7 +570,10 @@ async def handle_order_requests(
     order: BrokerdOrder
 
     async for request_msg in ems_order_stream:
-        log.info(f'Received order request {request_msg}')
+        log.info(
+            'Received order request:\n'
+            f'{pformat(request_msg)}'
+        )
 
         action = request_msg['action']
 
@@ -628,6 +632,7 @@ async def handle_order_requests(
                     # update the internal pairing of oid to krakens
                     # txid with the new txid that is returned on edit
                     reqid = resp['result']['txid']
+
                 # deliver ack that order has been submitted to broker routing
                 await ems_order_stream.send(
                     BrokerdOrderAck(
@@ -788,7 +793,10 @@ async def trades_dialogue(
         # Get websocket token for authenticated data stream
         # Assert that a token was actually received.
         resp = await client.endpoint('GetWebSocketsToken', {})
+
+        # lol wtf is this..
         assert resp['error'] == []
+
         token = resp['result']['token']
 
         async with (
diff --git a/piker/clearing/_ems.py b/piker/clearing/_ems.py
index a5d04f0c..17f9be1a 100644
--- a/piker/clearing/_ems.py
+++ b/piker/clearing/_ems.py
@@ -80,7 +80,9 @@ def mk_check(
 
         return check_lt
 
-    raise ValueError('trigger: {trigger_price}, last: {known_last}')
+    raise ValueError(
+        f'trigger: {trigger_price}, last: {known_last}'
+    )
 
 
 @dataclass
@@ -561,7 +563,10 @@ async def translate_and_relay_brokerd_events(
 
         name = brokerd_msg['name']
 
-        log.info(f'Received broker trade event:\n{pformat(brokerd_msg)}')
+        log.info(
+            f'Received broker trade event:\n'
+            f'{pformat(brokerd_msg)}'
+        )
 
         if name == 'position':
 
@@ -613,19 +618,28 @@ async def translate_and_relay_brokerd_events(
             # packed at submission since we already know it ahead of
             # time
             paper = brokerd_msg['broker_details'].get('paper_info')
+            ext = brokerd_msg['broker_details'].get('external')
             if paper:
                 # paperboi keeps the ems id up front
                 oid = paper['oid']
 
-            else:
+            elif ext:
                 # may be an order msg specified as "external" to the
                 # piker ems flow (i.e. generated by some other
                 # external broker backend client (like tws for ib)
-                ext = brokerd_msg['broker_details'].get('external')
-                if ext:
-                    log.error(f"External trade event {ext}")
+                log.error(f"External trade event {ext}")
 
                 continue
+
+            else:
+                # something is out of order, we don't have an oid for
+                # this broker-side message.
+                log.error(
+                    'Unknown oid:{oid} for msg:\n'
+                    f'{pformat(brokerd_msg)}'
+                    'Unable to relay message to client side!?'
+                )
+
         else:
             # check for existing live flow entry
             entry = book._ems_entries.get(oid)
@@ -823,7 +837,9 @@ async def process_client_order_cmds(
                 if reqid:
 
                     # send cancel to brokerd immediately!
-                    log.info("Submitting cancel for live order {reqid}")
+                    log.info(
+                        f'Submitting cancel for live order {reqid}'
+                    )
 
                     await brokerd_order_stream.send(msg.dict())
 
diff --git a/piker/config.py b/piker/config.py
index cf946405..d1926dec 100644
--- a/piker/config.py
+++ b/piker/config.py
@@ -1,5 +1,5 @@
 # piker: trading gear for hackers
-# Copyright (C) 2018-present  Tyler Goodlet (in stewardship of piker0)
+# Copyright (C) 2018-present  Tyler Goodlet (in stewardship for pikers)
 
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU Affero General Public License as published by
@@ -16,6 +16,7 @@
 
 """
 Broker configuration mgmt.
+
 """
 import platform
 import sys
@@ -50,7 +51,7 @@ def get_app_dir(app_name, roaming=True, force_posix=False):
     Unix (POSIX):
       ``~/.foo-bar``
     Win XP (roaming):
-      ``C:\Documents and Settings\<user>\Local Settings\Application Data\Foo Bar``
+      ``C:\Documents and Settings\<user>\Local Settings\Application Data\Foo``
     Win XP (not roaming):
       ``C:\Documents and Settings\<user>\Application Data\Foo Bar``
     Win 7 (roaming):
@@ -81,7 +82,8 @@ def get_app_dir(app_name, roaming=True, force_posix=False):
             folder = os.path.expanduser("~")
         return os.path.join(folder, app_name)
     if force_posix:
-        return os.path.join(os.path.expanduser("~/.{}".format(_posixify(app_name))))
+        return os.path.join(
+            os.path.expanduser("~/.{}".format(_posixify(app_name))))
     if sys.platform == "darwin":
         return os.path.join(
             os.path.expanduser("~/Library/Application Support"), app_name
@@ -107,7 +109,12 @@ if _parent_user:
         ]
     )
 
-_file_name = 'brokers.toml'
+_conf_names: set[str] = {
+    'brokers',
+    'trades',
+    'watchlists',
+}
+
 _watchlists_data_path = os.path.join(_config_dir, 'watchlists.json')
 _context_defaults = dict(
     default_map={
@@ -129,23 +136,43 @@ def _override_config_dir(
     _config_dir = path
 
 
-def get_broker_conf_path():
+def _conf_fn_w_ext(
+    name: str,
+) -> str:
+    # change this if we ever change the config file format.
+    return f'{name}.toml'
+
+
+def get_conf_path(
+    conf_name: str = 'brokers',
+
+) -> str:
     """Return the default config path normally under
     ``~/.config/piker`` on linux.
 
     Contains files such as:
     - brokers.toml
     - watchlists.toml
+    - trades.toml
+
+    # maybe coming soon ;)
     - signals.toml
     - strats.toml
 
     """
-    return os.path.join(_config_dir, _file_name)
+    assert conf_name in _conf_names
+    fn = _conf_fn_w_ext(conf_name)
+    return os.path.join(
+        _config_dir,
+        fn,
+    )
 
 
 def repodir():
-    """Return the abspath to the repo directory.
-    """
+    '''
+    Return the abspath to the repo directory.
+
+    '''
     dirpath = os.path.abspath(
         # we're 3 levels down in **this** module file
         dirname(dirname(os.path.realpath(__file__)))
@@ -154,16 +181,27 @@ def repodir():
 
 
 def load(
+    conf_name: str = 'brokers',
     path: str = None
+
 ) -> (dict, str):
-    """Load broker config.
-    """
-    path = path or get_broker_conf_path()
+    '''
+    Load config file by name.
+
+    '''
+    path = path or get_conf_path(conf_name)
     if not os.path.isfile(path):
-        shutil.copyfile(
-            os.path.join(repodir(), 'config', 'brokers.toml'),
-            path,
+        fn = _conf_fn_w_ext(conf_name)
+
+        template = os.path.join(
+            repodir(),
+            'config',
+            fn
         )
+        # try to copy in a template config to the user's directory
+        # if one exists.
+        if os.path.isfile(template):
+            shutil.copyfile(template, path)
 
     config = toml.load(path)
     log.debug(f"Read config file {path}")
@@ -172,13 +210,17 @@ def load(
 
 def write(
     config: dict,  # toml config as dict
+    name: str = 'brokers',
     path: str = None,
+
 ) -> None:
-    """Write broker config to disk.
+    ''''
+    Write broker config to disk.
 
     Create a ``brokers.ini`` file if one does not exist.
-    """
-    path = path or get_broker_conf_path()
+
+    '''
+    path = path or get_conf_path(name)
     dirname = os.path.dirname(path)
     if not os.path.isdir(dirname):
         log.debug(f"Creating config dir {_config_dir}")
@@ -188,7 +230,10 @@ def write(
         raise ValueError(
             "Watch out you're trying to write a blank config!")
 
-    log.debug(f"Writing config file {path}")
+    log.debug(
+        f"Writing config `{name}` file to:\n"
+        f"{path}"
+    )
     with open(path, 'w') as cf:
         return toml.dump(config, cf)
 
@@ -218,4 +263,5 @@ def load_accounts(
 
     # our default paper engine entry
     accounts['paper'] = None
+
     return accounts
diff --git a/piker/data/_ahab.py b/piker/data/_ahab.py
index 0f96ecaa..fea19a4d 100644
--- a/piker/data/_ahab.py
+++ b/piker/data/_ahab.py
@@ -98,8 +98,6 @@ async def open_docker(
     finally:
         if client:
             client.close()
-            for c in client.containers.list():
-                c.kill()
 
 
 class Container:
diff --git a/piker/data/_sampling.py b/piker/data/_sampling.py
index 8bc677cf..77b15d7f 100644
--- a/piker/data/_sampling.py
+++ b/piker/data/_sampling.py
@@ -22,7 +22,7 @@ financial data flows.
 from __future__ import annotations
 from collections import Counter
 import time
-from typing import TYPE_CHECKING, Optional
+from typing import TYPE_CHECKING, Optional, Union
 
 import tractor
 import trio
@@ -32,6 +32,7 @@ from ..log import get_logger
 
 if TYPE_CHECKING:
     from ._sharedmem import ShmArray
+    from .feed import _FeedsBus
 
 log = get_logger(__name__)
 
@@ -142,11 +143,17 @@ async def broadcast(
     shm: Optional[ShmArray] = None,
 
 ) -> None:
-    # broadcast the buffer index step to any subscribers for
-    # a given sample period.
+    '''
+    Broadcast the given ``shm: ShmArray``'s buffer index step to any
+    subscribers for a given sample period.
+
+    The sent msg will include the first and last index which slice into
+    the buffer's non-empty data.
+
+    '''
     subs = sampler.subscribers.get(delay_s, ())
 
-    last = -1
+    first = last = -1
 
     if shm is None:
         periods = sampler.ohlcv_shms.keys()
@@ -156,11 +163,16 @@ async def broadcast(
         if periods:
             lowest = min(periods)
             shm = sampler.ohlcv_shms[lowest][0]
+            first = shm._first.value
             last = shm._last.value
 
     for stream in subs:
         try:
-            await stream.send({'index': last})
+            await stream.send({
+                'first': first,
+                'last': last,
+                'index': last,
+            })
         except (
             trio.BrokenResourceError,
             trio.ClosedResourceError
@@ -168,7 +180,12 @@ async def broadcast(
             log.error(
                 f'{stream._ctx.chan.uid} dropped connection'
             )
-            subs.remove(stream)
+            try:
+                subs.remove(stream)
+            except ValueError:
+                log.warning(
+                    f'{stream._ctx.chan.uid} sub already removed!?'
+                )
 
 
 @tractor.context
@@ -203,7 +220,7 @@ async def iter_ohlc_periods(
 
 async def sample_and_broadcast(
 
-    bus: '_FeedsBus',  # noqa
+    bus: _FeedsBus,  # noqa
     shm: ShmArray,
     quote_stream: trio.abc.ReceiveChannel,
     brokername: str,
@@ -282,7 +299,13 @@ async def sample_and_broadcast(
             # end up triggering backpressure which which will
             # eventually block this producer end of the feed and
             # thus other consumers still attached.
-            subs = bus._subscribers[broker_symbol.lower()]
+            subs: list[
+                tuple[
+                    Union[tractor.MsgStream, trio.MemorySendChannel],
+                    tractor.Context,
+                    Optional[float],  # tick throttle in Hz
+                ]
+            ] = bus._subscribers[broker_symbol.lower()]
 
             # NOTE: by default the broker backend doesn't append
             # it's own "name" into the fqsn schema (but maybe it
@@ -291,7 +314,7 @@ async def sample_and_broadcast(
             bsym = f'{broker_symbol}.{brokername}'
             lags: int = 0
 
-            for (stream, tick_throttle) in subs:
+            for (stream, ctx, tick_throttle) in subs:
 
                 try:
                     with trio.move_on_after(0.2) as cs:
@@ -303,25 +326,41 @@ async def sample_and_broadcast(
                                     (bsym, quote)
                                 )
                             except trio.WouldBlock:
-                                ctx = getattr(stream, '_ctx', None)
+                                chan = ctx.chan
                                 if ctx:
                                     log.warning(
                                         f'Feed overrun {bus.brokername} ->'
-                                        f'{ctx.channel.uid} !!!'
+                                        f'{chan.uid} !!!'
                                     )
                                 else:
                                     key = id(stream)
                                     overruns[key] += 1
                                     log.warning(
-                                        f'Feed overrun {bus.brokername} -> '
+                                        f'Feed overrun {broker_symbol}'
+                                        '@{bus.brokername} -> '
                                         f'feed @ {tick_throttle} Hz'
                                     )
                                     if overruns[key] > 6:
-                                        log.warning(
-                                            f'Dropping consumer {stream}'
-                                        )
-                                        await stream.aclose()
-                                        raise trio.BrokenResourceError
+                                        # TODO: should we check for the
+                                        # context being cancelled? this
+                                        # could happen but the
+                                        # channel-ipc-pipe is still up.
+                                        if not chan.connected():
+                                            log.warning(
+                                                'Dropping broken consumer:\n'
+                                                f'{broker_symbol}:'
+                                                f'{ctx.cid}@{chan.uid}'
+                                            )
+                                            await stream.aclose()
+                                            raise trio.BrokenResourceError
+                                        else:
+                                            log.warning(
+                                                'Feed getting overrun bro!\n'
+                                                f'{broker_symbol}:'
+                                                f'{ctx.cid}@{chan.uid}'
+                                            )
+                                            continue
+
                         else:
                             await stream.send(
                                 {bsym: quote}
@@ -337,11 +376,12 @@ async def sample_and_broadcast(
                     trio.ClosedResourceError,
                     trio.EndOfChannel,
                 ):
-                    ctx = getattr(stream, '_ctx', None)
+                    chan = ctx.chan
                     if ctx:
                         log.warning(
-                            f'{ctx.chan.uid} dropped  '
-                            '`brokerd`-quotes-feed connection'
+                            'Dropped `brokerd`-quotes-feed connection:\n'
+                            f'{broker_symbol}:'
+                            f'{ctx.cid}@{chan.uid}'
                         )
                     if tick_throttle:
                         assert stream._closed
@@ -354,7 +394,11 @@ async def sample_and_broadcast(
                     try:
                         subs.remove((stream, tick_throttle))
                     except ValueError:
-                        log.error(f'{stream} was already removed from subs!?')
+                        log.error(
+                            f'Stream was already removed from subs!?\n'
+                            f'{broker_symbol}:'
+                            f'{ctx.cid}@{chan.uid}'
+                        )
 
 
 # TODO: a less naive throttler, here's some snippets:
@@ -466,6 +510,7 @@ async def uniform_rate_send(
             # if the feed consumer goes down then drop
             # out of this rate limiter
             log.warning(f'{stream} closed')
+            await stream.aclose()
             return
 
         # reset send cycle state
diff --git a/piker/data/_sharedmem.py b/piker/data/_sharedmem.py
index 8848ec1c..1172fc7b 100644
--- a/piker/data/_sharedmem.py
+++ b/piker/data/_sharedmem.py
@@ -20,6 +20,7 @@ NumPy compatible shared memory buffers for real-time IPC streaming.
 """
 from __future__ import annotations
 from sys import byteorder
+import time
 from typing import Optional
 from multiprocessing.shared_memory import SharedMemory, _USE_POSIX
 
@@ -98,7 +99,12 @@ class SharedInt:
         if _USE_POSIX:
             # We manually unlink to bypass all the "resource tracker"
             # nonsense meant for non-SC systems.
-            shm_unlink(self._shm.name)
+            name = self._shm.name
+            try:
+                shm_unlink(name)
+            except FileNotFoundError:
+                # might be a teardown race here?
+                log.warning(f'Shm for {name} already unlinked?')
 
 
 class _Token(BaseModel):
@@ -536,8 +542,26 @@ def attach_shm_array(
     if key in _known_tokens:
         assert _Token.from_msg(_known_tokens[key]) == token, "WTF"
 
+    # XXX: ugh, looks like due to the ``shm_open()`` C api we can't
+    # actually place files in a subdir, see discussion here:
+    # https://stackoverflow.com/a/11103289
+
     # attach to array buffer and view as per dtype
-    shm = SharedMemory(name=key)
+    _err: Optional[Exception] = None
+    for _ in range(3):
+        try:
+            shm = SharedMemory(
+                name=key,
+                create=False,
+            )
+            break
+        except OSError as oserr:
+            _err = oserr
+            time.sleep(0.1)
+    else:
+        if _err:
+            raise _err
+
     shmarr = np.ndarray(
         (size,),
         dtype=token.dtype,
diff --git a/piker/data/_source.py b/piker/data/_source.py
index 2f5f61ed..9afcb191 100644
--- a/piker/data/_source.py
+++ b/piker/data/_source.py
@@ -33,7 +33,7 @@ ohlc_fields = [
     ('high', float),
     ('low', float),
     ('close', float),
-    ('volume', int),
+    ('volume', float),
     ('bar_wap', float),
 ]
 
diff --git a/piker/data/feed.py b/piker/data/feed.py
index 605349e9..1165fddc 100644
--- a/piker/data/feed.py
+++ b/piker/data/feed.py
@@ -33,6 +33,7 @@ from typing import (
     Generator,
     Awaitable,
     TYPE_CHECKING,
+    Union,
 )
 
 import trio
@@ -40,12 +41,12 @@ from trio.abc import ReceiveChannel
 from trio_typing import TaskStatus
 import trimeter
 import tractor
+from tractor.trionics import maybe_open_context
 from pydantic import BaseModel
 import pendulum
 import numpy as np
 
 from ..brokers import get_brokermod
-from .._cacheables import maybe_open_context
 from ..calc import humanize
 from ..log import get_logger, get_console_log
 from .._daemon import (
@@ -116,7 +117,13 @@ class _FeedsBus(BaseModel):
     # https://github.com/samuelcolvin/pydantic/issues/2816
     _subscribers: dict[
         str,
-        list[tuple[tractor.MsgStream, Optional[float]]]
+        list[
+            tuple[
+                Union[tractor.MsgStream, trio.MemorySendChannel],
+                tractor.Context,
+                Optional[float],  # tick throttle in Hz
+            ]
+        ]
     ] = {}
 
     async def start_task(
@@ -228,7 +235,7 @@ def diff_history(
                 # the + 1 is because ``last_tsdb_dt`` is pulled from
                 # the last row entry for the ``'time'`` field retreived
                 # from the tsdb.
-                to_push = array[abs(s_diff)+1:]
+                to_push = array[abs(s_diff) + 1:]
 
             else:
                 # pass back only the portion of the array that is
@@ -251,6 +258,7 @@ async def start_backfill(
     last_tsdb_dt: Optional[datetime] = None,
     storage: Optional[Storage] = None,
     write_tsdb: bool = True,
+    tsdb_is_up: bool = False,
 
     task_status: TaskStatus[trio.CancelScope] = trio.TASK_STATUS_IGNORED,
 
@@ -266,8 +274,8 @@ async def start_backfill(
 
         # sample period step size in seconds
         step_size_s = (
-            pendulum.from_timestamp(times[-1]) -
-            pendulum.from_timestamp(times[-2])
+            pendulum.from_timestamp(times[-1])
+            - pendulum.from_timestamp(times[-2])
         ).seconds
 
         # "frame"'s worth of sample period steps in seconds
@@ -292,25 +300,33 @@ async def start_backfill(
         # let caller unblock and deliver latest history frame
         task_status.started((shm, start_dt, end_dt, bf_done))
 
+        # based on the sample step size, maybe load a certain amount history
         if last_tsdb_dt is None:
-            # maybe a better default (they don't seem to define epoch?!)
-
-            # based on the sample step size load a certain amount
-            # history
-            if step_size_s == 1:
-                last_tsdb_dt = pendulum.now().subtract(days=2)
-
-            elif step_size_s == 60:
-                last_tsdb_dt = pendulum.now().subtract(years=2)
-
-            else:
+            if step_size_s not in (1, 60):
                 raise ValueError(
                     '`piker` only needs to support 1m and 1s sampling '
                     'but ur api is trying to deliver a longer '
                     f'timeframe of {step_size_s} ' 'seconds.. so ye, dun '
-                    'do dat bruh.'
+                    'do dat brudder.'
                 )
 
+            # when no tsdb "last datum" is provided, we just load
+            # some near-term history.
+            periods = {
+                1: {'days': 1},
+                60: {'days': 14},
+            }
+
+            if tsdb_is_up:
+                # do a decently sized backfill and load it into storage.
+                periods = {
+                    1: {'days': 6},
+                    60: {'years': 2},
+                }
+
+            kwargs = periods[step_size_s]
+            last_tsdb_dt = start_dt.subtract(**kwargs)
+
         # configure async query throttling
         erlangs = config.get('erlangs', 1)
         rate = config.get('rate', 1)
@@ -328,7 +344,7 @@ async def start_backfill(
                 log.debug(f'New datetime index:\n{pformat(dtrange)}')
 
                 for end_dt in dtrange:
-                    log.warning(f'Yielding next frame start {end_dt}')
+                    log.info(f'Yielding next frame start {end_dt}')
                     start = yield end_dt
 
                     # if caller sends a new start date, reset to that
@@ -568,8 +584,8 @@ async def start_backfill(
                                     start_dt,
                                     end_dt,
                                 ) = await get_ohlc_frame(
-                                        input_end_dt=last_shm_prepend_dt,
-                                        iter_dts_gen=idts,
+                                    input_end_dt=last_shm_prepend_dt,
+                                    iter_dts_gen=idts,
                                 )
                                 last_epoch = to_push['time'][-1]
                                 diff = start - last_epoch
@@ -712,6 +728,7 @@ async def manage_history(
                     bfqsn,
                     shm,
                     last_tsdb_dt=last_tsdb_dt,
+                    tsdb_is_up=True,
                     storage=storage,
                 )
             )
@@ -795,6 +812,15 @@ async def manage_history(
 
                     # manually trigger step update to update charts/fsps
                     # which need an incremental update.
+                    # NOTE: the way this works is super duper
+                    # un-intuitive right now:
+                    # - the broadcaster fires a msg to the fsp subsystem.
+                    # - fsp subsys then checks for a sample step diff and
+                    #   possibly recomputes prepended history.
+                    # - the fsp then sends back to the parent actor
+                    #   (usually a chart showing graphics for said fsp)
+                    #   which tells the chart to conduct a manual full
+                    #   graphics loop cycle.
                     for delay_s in sampler.subscribers:
                         await broadcast(delay_s)
 
@@ -994,7 +1020,7 @@ async def open_feed_bus(
     brokername: str,
     symbol: str,  # normally expected to the broker-specific fqsn
     loglevel: str,
-    tick_throttle:  Optional[float] = None,
+    tick_throttle: Optional[float] = None,
     start_stream: bool = True,
 
 ) -> None:
@@ -1098,10 +1124,10 @@ async def open_feed_bus(
                 recv,
                 stream,
             )
-            sub = (send, tick_throttle)
+            sub = (send, ctx, tick_throttle)
 
         else:
-            sub = (stream, tick_throttle)
+            sub = (stream, ctx, tick_throttle)
 
         subs = bus._subscribers[bfqsn]
         subs.append(sub)
@@ -1255,7 +1281,7 @@ async def install_brokerd_search(
                 # a backend module?
                 pause_period=getattr(
                     brokermod, '_search_conf', {}
-                    ).get('pause_period', 0.0616),
+                ).get('pause_period', 0.0616),
             ):
                 yield
 
diff --git a/piker/data/marketstore.py b/piker/data/marketstore.py
index e1fb38d5..4d1c91ad 100644
--- a/piker/data/marketstore.py
+++ b/piker/data/marketstore.py
@@ -230,8 +230,8 @@ _ohlcv_dt = [
     # ohlcv sampling
     ('Open', 'f4'),
     ('High', 'f4'),
-    ('Low', 'i8'),
-    ('Close', 'i8'),
+    ('Low', 'f4'),
+    ('Close', 'f4'),
     ('Volume', 'f4'),
 ]
 
@@ -547,6 +547,17 @@ class Storage:
                 if err:
                     raise MarketStoreError(err)
 
+    # XXX: currently the only way to do this is through the CLI:
+
+    # sudo ./marketstore connect --dir ~/.config/piker/data
+    # >> \show mnq.globex.20220617.ib/1Sec/OHLCV 2022-05-15
+    # and this seems to block and use up mem..
+    # >> \trim mnq.globex.20220617.ib/1Sec/OHLCV 2022-05-15
+
+    # relevant source code for this is here:
+    # https://github.com/alpacahq/marketstore/blob/master/cmd/connect/session/trim.go#L14
+    # def delete_range(self, start_dt, end_dt) -> None:
+    #     ...
 
 @acm
 async def open_storage_client(
@@ -628,12 +639,13 @@ async def tsdb_history_update(
             tsdb_arrays = await storage.read_ohlcv(fqsn)
             # hist diffing
             if tsdb_arrays:
-                onesec = tsdb_arrays[1]
-
-                # these aren't currently used but can be referenced from
-                # within the embedded ipython shell below.
-                to_append = ohlcv[ohlcv['time'] > onesec['Epoch'][-1]]
-                to_prepend = ohlcv[ohlcv['time'] < onesec['Epoch'][0]]
+                for secs in (1, 60):
+                    ts = tsdb_arrays.get(secs)
+                    if ts is not None and len(ts):
+                        # these aren't currently used but can be referenced from
+                        # within the embedded ipython shell below.
+                        to_append = ohlcv[ohlcv['time'] > ts['Epoch'][-1]]
+                        to_prepend = ohlcv[ohlcv['time'] < ts['Epoch'][0]]
 
             profiler('Finished db arrays diffs')
 
diff --git a/piker/fsp/_engine.py b/piker/fsp/_engine.py
index 0776c7a2..cf45c40e 100644
--- a/piker/fsp/_engine.py
+++ b/piker/fsp/_engine.py
@@ -369,7 +369,12 @@ async def cascade(
                     # always trigger UI refresh after history update,
                     # see ``piker.ui._fsp.FspAdmin.open_chain()`` and
                     # ``piker.ui._display.trigger_update()``.
-                    await client_stream.send('update')
+                    await client_stream.send({
+                        'fsp_update': {
+                            'key': dst_shm_token,
+                            'first': dst._first.value,
+                            'last': dst._last.value,
+                    }})
                     return tracker, index
 
                 def is_synced(
diff --git a/piker/log.py b/piker/log.py
index 7c8bb798..804e09dc 100644
--- a/piker/log.py
+++ b/piker/log.py
@@ -25,10 +25,13 @@ from pygments import highlight, lexers, formatters
 
 # Makes it so we only see the full module name when using ``__name__``
 # without the extra "piker." prefix.
-_proj_name = 'piker'
+_proj_name: str = 'piker'
 
 
-def get_logger(name: str = None) -> logging.Logger:
+def get_logger(
+    name: str = None,
+
+) -> logging.Logger:
     '''Return the package log or a sub-log for `name` if provided.
     '''
     return tractor.log.get_logger(name=name, _root_name=_proj_name)
diff --git a/piker/ui/_axes.py b/piker/ui/_axes.py
index 93ac7af7..7ba52055 100644
--- a/piker/ui/_axes.py
+++ b/piker/ui/_axes.py
@@ -223,8 +223,9 @@ class DynamicDateAxis(Axis):
     ) -> list[str]:
 
         chart = self.linkedsplits.chart
-        bars = chart._arrays[chart.name]
-        shm = self.linkedsplits.chart._shm
+        flow = chart._flows[chart.name]
+        shm = flow.shm
+        bars = shm.array
         first = shm._first.value
 
         bars_len = len(bars)
diff --git a/piker/ui/_chart.py b/piker/ui/_chart.py
index a3a97164..7b40f0d7 100644
--- a/piker/ui/_chart.py
+++ b/piker/ui/_chart.py
@@ -34,9 +34,7 @@ from PyQt5.QtWidgets import (
     QVBoxLayout,
     QSplitter,
 )
-import msgspec
 import numpy as np
-# from pydantic import BaseModel
 import pyqtgraph as pg
 import trio
 
@@ -49,9 +47,13 @@ from ._cursor import (
     Cursor,
     ContentsLabel,
 )
+from ..data._sharedmem import ShmArray
 from ._l1 import L1Labels
 from ._ohlc import BarItems
-from ._curve import FastAppendCurve
+from ._curve import (
+    Curve,
+    StepCurve,
+)
 from ._style import (
     hcolor,
     CHART_MARGINS,
@@ -60,15 +62,12 @@ from ._style import (
 )
 from ..data.feed import Feed
 from ..data._source import Symbol
-from ..data._sharedmem import (
-    ShmArray,
-    # _Token,
-)
 from ..log import get_logger
 from ._interaction import ChartView
 from ._forms import FieldsForm
 from .._profile import pg_profile_enabled, ms_slower_then
 from ._overlay import PlotItemOverlay
+from ._flows import Flow
 
 if TYPE_CHECKING:
     from ._display import DisplayState
@@ -419,7 +418,7 @@ class LinkedSplits(QWidget):
         self,
 
         symbol: Symbol,
-        array: np.ndarray,
+        shm: ShmArray,
         sidepane: FieldsForm,
 
         style: str = 'bar',
@@ -444,7 +443,7 @@ class LinkedSplits(QWidget):
         self.chart = self.add_plot(
 
             name=symbol.key,
-            array=array,
+            shm=shm,
             style=style,
             _is_main=True,
 
@@ -472,7 +471,7 @@ class LinkedSplits(QWidget):
         self,
 
         name: str,
-        array: np.ndarray,
+        shm: ShmArray,
 
         array_key: Optional[str] = None,
         style: str = 'line',
@@ -516,7 +515,6 @@ class LinkedSplits(QWidget):
             name=name,
             data_key=array_key or name,
 
-            array=array,
             parent=qframe,
             linkedsplits=self,
             axisItems=axes,
@@ -580,7 +578,7 @@ class LinkedSplits(QWidget):
 
             graphics, data_key = cpw.draw_ohlc(
                 name,
-                array,
+                shm,
                 array_key=array_key
             )
             self.cursor.contents_labels.add_label(
@@ -594,7 +592,7 @@ class LinkedSplits(QWidget):
             add_label = True
             graphics, data_key = cpw.draw_curve(
                 name,
-                array,
+                shm,
                 array_key=array_key,
                 color='default_light',
             )
@@ -603,7 +601,7 @@ class LinkedSplits(QWidget):
             add_label = True
             graphics, data_key = cpw.draw_curve(
                 name,
-                array,
+                shm,
                 array_key=array_key,
                 step_mode=True,
                 color='davies',
@@ -691,7 +689,6 @@ class ChartPlotWidget(pg.PlotWidget):
 
         # the "data view" we generate graphics from
         name: str,
-        array: np.ndarray,
         data_key: str,
         linkedsplits: LinkedSplits,
 
@@ -744,14 +741,6 @@ class ChartPlotWidget(pg.PlotWidget):
         self._max_l1_line_len: float = 0
 
         # self.setViewportMargins(0, 0, 0, 0)
-        # self._ohlc = array  # readonly view of ohlc data
-
-        # TODO: move to Aggr above XD
-        # readonly view of data arrays
-        self._arrays = {
-            self.data_key: array,
-        }
-        self._graphics = {}  # registry of underlying graphics
 
         # registry of overlay curve names
         self._flows: dict[str, Flow] = {}
@@ -767,7 +756,6 @@ class ChartPlotWidget(pg.PlotWidget):
         # show background grid
         self.showGrid(x=False, y=True, alpha=0.3)
 
-        self.default_view()
         self.cv.enable_auto_yrange()
 
         self.pi_overlay: PlotItemOverlay = PlotItemOverlay(self.plotItem)
@@ -816,14 +804,8 @@ class ChartPlotWidget(pg.PlotWidget):
         Return a range tuple for the bars present in view.
 
         '''
-        l, r = self.view_range()
-        array = self._arrays[self.name]
-        start, stop = self._xrange = (
-            array[0]['index'],
-            array[-1]['index'],
-        )
-        lbar = max(l, start)
-        rbar = min(r, stop)
+        main_flow = self._flows[self.name]
+        ifirst, l, lbar, rbar, r, ilast = main_flow.datums_range()
         return l, lbar, rbar, r
 
     def curve_width_pxs(
@@ -877,40 +859,51 @@ class ChartPlotWidget(pg.PlotWidget):
 
     def default_view(
         self,
-        steps_on_screen: Optional[int] = None
+        bars_from_y: int = 3000,
 
     ) -> None:
         '''
         Set the view box to the "default" startup view of the scene.
 
         '''
-        try:
-            index = self._arrays[self.name]['index']
-        except IndexError:
-            log.warning(f'array for {self.name} not loaded yet?')
+        flow = self._flows.get(self.name)
+        if not flow:
+            log.warning(f'`Flow` for {self.name} not loaded yet?')
             return
 
+        index = flow.shm.array['index']
         xfirst, xlast = index[0], index[-1]
         l, lbar, rbar, r = self.bars_range()
-
-        marker_pos, l1_len = self.pre_l1_xs()
-        end = xlast + l1_len + 1
+        view = self.view
 
         if (
             rbar < 0
             or l < xfirst
+            or l < 0
             or (rbar - lbar) < 6
         ):
-            # set fixed bars count on screen that approx includes as
+            # TODO: set fixed bars count on screen that approx includes as
             # many bars as possible before a downsample line is shown.
-            begin = xlast - round(6116 / 6)
+            begin = xlast - bars_from_y
+            view.setXRange(
+                min=begin,
+                max=xlast,
+                padding=0,
+            )
+            # re-get range
+            l, lbar, rbar, r = self.bars_range()
 
-        else:
-            begin = end - (r - l)
+        # we get the L1 spread label "length" in view coords
+        # terms now that we've scaled either by user control
+        # or to the default set of bars as per the immediate block
+        # above.
+        marker_pos, l1_len = self.pre_l1_xs()
+        end = xlast + l1_len + 1
+        begin = end - (r - l)
 
         # for debugging
         # print(
-        #     f'bars range: {brange}\n'
+        #     # f'bars range: {brange}\n'
         #     f'xlast: {xlast}\n'
         #     f'marker pos: {marker_pos}\n'
         #     f'l1 len: {l1_len}\n'
@@ -922,14 +915,13 @@ class ChartPlotWidget(pg.PlotWidget):
         if self._static_yrange == 'axis':
             self._static_yrange = None
 
-        view = self.view
         view.setXRange(
             min=begin,
             max=end,
             padding=0,
         )
-        view._set_yrange()
         self.view.maybe_downsample_graphics()
+        view._set_yrange()
         try:
             self.linked.graphics_cycle()
         except IndexError:
@@ -960,7 +952,7 @@ class ChartPlotWidget(pg.PlotWidget):
     def draw_ohlc(
         self,
         name: str,
-        data: np.ndarray,
+        shm: ShmArray,
 
         array_key: Optional[str] = None,
 
@@ -980,15 +972,12 @@ class ChartPlotWidget(pg.PlotWidget):
         # the np array buffer to be drawn on next render cycle
         self.plotItem.addItem(graphics)
 
-        # draw after to allow self.scene() to work...
-        graphics.draw_from_data(data)
-
         data_key = array_key or name
-        self._graphics[data_key] = graphics
 
         self._flows[data_key] = Flow(
             name=name,
             plot=self.plotItem,
+            _shm=shm,
             is_ohlc=True,
             graphics=graphics,
         )
@@ -1058,20 +1047,21 @@ class ChartPlotWidget(pg.PlotWidget):
         self,
 
         name: str,
-        data: np.ndarray,
+        shm: ShmArray,
 
         array_key: Optional[str] = None,
         overlay: bool = False,
         color: Optional[str] = None,
         add_label: bool = True,
         pi: Optional[pg.PlotItem] = None,
+        step_mode: bool = False,
 
         **pdi_kwargs,
 
     ) -> (pg.PlotDataItem, str):
         '''
         Draw a "curve" (line plot graphics) for the provided data in
-        the input array ``data``.
+        the input shm array ``shm``.
 
         '''
         color = color or self.pen_color or 'default_light'
@@ -1081,40 +1071,26 @@ class ChartPlotWidget(pg.PlotWidget):
 
         data_key = array_key or name
 
-        # yah, we wrote our own B)
-        curve = FastAppendCurve(
-            y=data[data_key],
-            x=data['index'],
-            # antialias=True,
+        curve_type = {
+            None: Curve,
+            'step': StepCurve,
+            # TODO:
+            # 'bars': BarsItems
+        }['step' if step_mode else None]
+
+        curve = curve_type(
             name=name,
-
-            # XXX: pretty sure this is just more overhead
-            # on data reads and makes graphics rendering no faster
-            # clipToView=True,
-
             **pdi_kwargs,
         )
 
-        # XXX: see explanation for different caching modes:
-        # https://stackoverflow.com/a/39410081
-        # seems to only be useful if we don't re-generate the entire
-        # QPainterPath every time
-        # curve.setCacheMode(QtWidgets.QGraphicsItem.DeviceCoordinateCache)
-
-        # don't ever use this - it's a colossal nightmare of artefacts
-        # and is disastrous for performance.
-        # curve.setCacheMode(QtWidgets.QGraphicsItem.ItemCoordinateCache)
-
-        # register curve graphics and backing array for name
-        self._graphics[name] = curve
-        self._arrays[data_key] = data
-
         pi = pi or self.plotItem
 
         self._flows[data_key] = Flow(
             name=name,
             plot=pi,
+            _shm=shm,
             is_ohlc=False,
+            # register curve graphics with this flow
             graphics=curve,
         )
 
@@ -1175,16 +1151,11 @@ class ChartPlotWidget(pg.PlotWidget):
         )
         return last
 
-    def update_graphics_from_array(
+    def update_graphics_from_flow(
         self,
         graphics_name: str,
-
-        array: Optional[np.ndarray] = None,
         array_key: Optional[str] = None,
 
-        use_vr: bool = True,
-        render: bool = True,
-
         **kwargs,
 
     ) -> pg.GraphicsObject:
@@ -1192,63 +1163,11 @@ class ChartPlotWidget(pg.PlotWidget):
         Update the named internal graphics from ``array``.
 
         '''
-        if array is not None:
-            assert len(array)
-
-        data_key = array_key or graphics_name
-        if graphics_name not in self._flows:
-            data_key = self.name
-
-        if array is not None:
-            # write array to internal graphics table
-            self._arrays[data_key] = array
-        else:
-            array = self._arrays[data_key]
-
-        # array key and graphics "name" might be different..
-        graphics = self._graphics[graphics_name]
-
-        # compute "in-view" indices
-        l, lbar, rbar, r = self.bars_range()
-        indexes = array['index']
-        ifirst = indexes[0]
-        ilast = indexes[-1]
-
-        lbar_i = max(l, ifirst) - ifirst
-        rbar_i = min(r, ilast) - ifirst
-
-        # TODO: we could do it this way as well no?
-        # to_draw = array[lbar - ifirst:(rbar - ifirst) + 1]
-        in_view = array[lbar_i: rbar_i + 1]
-
-        if (
-            not in_view.size
-            or not render
-        ):
-            return graphics
-
-        if isinstance(graphics, BarItems):
-            graphics.update_from_array(
-                array,
-                in_view,
-                view_range=(lbar_i, rbar_i) if use_vr else None,
-
-                **kwargs,
-            )
-
-        else:
-            graphics.update_from_array(
-                x=array['index'],
-                y=array[data_key],
-
-                x_iv=in_view['index'],
-                y_iv=in_view[data_key],
-                view_range=(lbar_i, rbar_i) if use_vr else None,
-
-                **kwargs
-            )
-
-        return graphics
+        flow = self._flows[array_key or graphics_name]
+        return flow.update_graphics(
+            array_key=array_key,
+            **kwargs,
+        )
 
     # def _label_h(self, yhigh: float, ylow: float) -> float:
     #     # compute contents label "height" in view terms
@@ -1295,7 +1214,7 @@ class ChartPlotWidget(pg.PlotWidget):
 
         # TODO: this should go onto some sort of
         # data-view thinger..right?
-        ohlc = self._shm.array
+        ohlc = self._flows[self.name].shm.array
 
         # XXX: not sure why the time is so off here
         # looks like we're gonna have to do some fixing..
@@ -1325,7 +1244,9 @@ class ChartPlotWidget(pg.PlotWidget):
     def maxmin(
         self,
         name: Optional[str] = None,
-        bars_range: Optional[tuple[int, int, int, int]] = None,
+        bars_range: Optional[tuple[
+            int, int, int, int, int, int
+        ]] = None,
 
     ) -> tuple[float, float]:
         '''
@@ -1334,16 +1255,14 @@ class ChartPlotWidget(pg.PlotWidget):
         If ``bars_range`` is provided use that range.
 
         '''
+        # print(f'Chart[{self.name}].maxmin()')
         profiler = pg.debug.Profiler(
-            msg=f'`{str(self)}.maxmin()` loop cycle for: `{self.name}`',
+            msg=f'`{str(self)}.maxmin(name={name})`: `{self.name}`',
             disabled=not pg_profile_enabled(),
-            gt=ms_slower_then,
+            ms_threshold=ms_slower_then,
             delayed=True,
         )
 
-        l, lbar, rbar, r = bars_range or self.bars_range()
-        profiler(f'{self.name} got bars range')
-
         # TODO: here we should instead look up the ``Flow.shm.array``
         # and read directly from shm to avoid copying to memory first
         # and then reading it again here.
@@ -1353,112 +1272,26 @@ class ChartPlotWidget(pg.PlotWidget):
             flow is None
         ):
             log.error(f"flow {flow_key} doesn't exist in chart {self.name} !?")
-            res = 0, 0
+            key = res = 0, 0
 
         else:
+            (
+                first,
+                l,
+                lbar,
+                rbar,
+                r,
+                last,
+            ) = bars_range or flow.datums_range()
+            profiler(f'{self.name} got bars range')
+
             key = round(lbar), round(rbar)
             res = flow.maxmin(*key)
-            profiler(f'yrange mxmn: {key} -> {res}')
             if res == (None, None):
                 log.error(
                     f"{flow_key} no mxmn for bars_range => {key} !?"
                 )
                 res = 0, 0
 
+        profiler(f'yrange mxmn: {key} -> {res}')
         return res
-
-
-# class FlowsTable(pydantic.BaseModel):
-#     '''
-#     Data-AGGRegate: high level API onto multiple (categorized)
-#     ``Flow``s with high level processing routines for
-#     multi-graphics computations and display.
-
-#     '''
-#     flows: dict[str, np.ndarray] = {}
-
-
-class Flow(msgspec.Struct):  # , frozen=True):
-    '''
-    (FinancialSignal-)Flow compound type which wraps a real-time
-    graphics (curve) and its backing data stream together for high level
-    access and control.
-
-    The intention is for this type to eventually be capable of shm-passing
-    of incrementally updated graphics stream data between actors.
-
-    '''
-    name: str
-    plot: pg.PlotItem
-    is_ohlc: bool = False
-    graphics: pg.GraphicsObject
-
-    # TODO: hackery to be able to set a shm later
-    # but whilst also allowing this type to hashable,
-    # likely will require serializable token that is used to attach
-    # to the underlying shm ref after startup?
-    _shm: Optional[ShmArray] = None  # currently, may be filled in "later"
-
-    # cache of y-range values per x-range input.
-    _mxmns: dict[tuple[int, int], tuple[float, float]] = {}
-
-    @property
-    def shm(self) -> ShmArray:
-        return self._shm
-
-    @shm.setter
-    def shm(self, shm: ShmArray) -> ShmArray:
-        self._shm = shm
-
-    def maxmin(
-        self,
-        lbar,
-        rbar,
-
-    ) -> tuple[float, float]:
-        '''
-        Compute the cached max and min y-range values for a given
-        x-range determined by ``lbar`` and ``rbar``.
-
-        '''
-        rkey = (lbar, rbar)
-        cached_result = self._mxmns.get(rkey)
-        if cached_result:
-            return cached_result
-
-        shm = self.shm
-        if shm is None:
-            mxmn = None
-
-        else:  # new block for profiling?..
-            arr = shm.array
-
-            # build relative indexes into shm array
-            # TODO: should we just add/use a method
-            # on the shm to do this?
-            ifirst = arr[0]['index']
-            slice_view = arr[
-                lbar - ifirst:
-                (rbar - ifirst) + 1
-            ]
-
-            if not slice_view.size:
-                mxmn = None
-
-            else:
-                if self.is_ohlc:
-                    ylow = np.min(slice_view['low'])
-                    yhigh = np.max(slice_view['high'])
-
-                else:
-                    view = slice_view[self.name]
-                    ylow = np.min(view)
-                    yhigh = np.max(view)
-
-                mxmn = ylow, yhigh
-
-            if mxmn is not None:
-                # cache new mxmn result
-                self._mxmns[rkey] = mxmn
-
-            return mxmn
diff --git a/piker/ui/_compression.py b/piker/ui/_compression.py
index adb42251..e9564359 100644
--- a/piker/ui/_compression.py
+++ b/piker/ui/_compression.py
@@ -138,50 +138,20 @@ def ohlc_flatten(
     return x, flat
 
 
-def ohlc_to_m4_line(
-    ohlc: np.ndarray,
-    px_width: int,
-
-    downsample: bool = False,
-    uppx: Optional[float] = None,
-    pretrace: bool = False,
-
-) -> tuple[np.ndarray, np.ndarray]:
-    '''
-    Convert an OHLC struct-array to a m4 downsampled 1-d array.
-
-    '''
-    xpts, flat = ohlc_flatten(
-        ohlc,
-        use_mxmn=pretrace,
-    )
-
-    if downsample:
-        bins, x, y = ds_m4(
-            xpts,
-            flat,
-            px_width=px_width,
-            uppx=uppx,
-            log_scale=bool(uppx)
-        )
-        x = np.broadcast_to(x[:, None], y.shape)
-        x = (x + np.array([-0.43, 0, 0, 0.43])).flatten()
-        y = y.flatten()
-
-        return x, y
-    else:
-        return xpts, flat
-
-
 def ds_m4(
     x: np.ndarray,
     y: np.ndarray,
+    # units-per-pixel-x(dimension)
+    uppx: float,
 
-    # this is the width of the data in view
-    # in display-device-local pixel units.
-    px_width: int,
-    uppx: Optional[float] = None,
-    log_scale: bool = True,
+    # XXX: troll zone / easter egg..
+    # want to mess with ur pal, pass in the actual
+    # pixel width here instead of uppx-proper (i.e. pass
+    # in our ``pg.GraphicsObject`` derivative's ``.px_width()``
+    # gto mega-trip-out ur bud). Hint, it used to be implemented
+    # (wrongly) using "pixel width", so check the git history ;)
+
+    xrange: Optional[float] = None,
 
 ) -> tuple[int, np.ndarray, np.ndarray]:
     '''
@@ -208,52 +178,49 @@ def ds_m4(
     # "i didn't show it in the sample code, but it's accounted for
     # in the start and end indices and number of bins"
 
-    # optionally log-scale down the "supposed pxs on screen"
-    # as the units-per-px (uppx) get's large.
-    if log_scale:
-        assert uppx, 'You must provide a `uppx` value to use log scaling!'
-
-        # scaler = 2**7 / (1 + math.log(uppx, 2))
-        scaler = round(
-            max(
-                # NOTE: found that a 16x px width brought greater
-                # detail, likely due to dpi scaling?
-                # px_width=px_width * 16,
-                2**7 / (1 + math.log(uppx, 2)),
-                1
-            )
-        )
-        px_width *= scaler
-
-    assert px_width > 1  # width of screen in pxs?
+    # should never get called unless actually needed
+    assert uppx > 1
 
     # NOTE: if we didn't pre-slice the data to downsample
     # you could in theory pass these as the slicing params,
     # do we care though since we can always just pre-slice the
     # input?
     x_start = x[0]  # x value start/lowest in domain
-    x_end = x[-1]  # x end value/highest in domain
+
+    if xrange is None:
+        x_end = x[-1]  # x end value/highest in domain
+        xrange = (x_end - x_start)
 
     # XXX: always round up on the input pixels
-    px_width = math.ceil(px_width)
+    # lnx = len(x)
+    # uppx *= max(4 / (1 + math.log(uppx, 2)), 1)
 
-    x_range = x_end - x_start
+    pxw = math.ceil(xrange / uppx)
 
-    # ratio of indexed x-value to width of raster in pixels.
-    # this is more or less, uppx: units-per-pixel.
-    w = x_range / float(px_width)
+    # scale up the frame "width" directly with uppx
+    w = uppx
 
     # ensure we make more then enough
     # frames (windows) for the output pixel
-    frames = px_width
+    frames = pxw
 
     # if we have more and then exact integer's
     # (uniform quotient output) worth of datum-domain-points
     # per windows-frame, add one more window to ensure
     # we have room for all output down-samples.
-    pts_per_pixel, r = divmod(len(x), frames)
+    pts_per_pixel, r = divmod(xrange, frames)
     if r:
+        # while r:
         frames += 1
+        pts_per_pixel, r = divmod(xrange, frames)
+
+    # print(
+    #     f'uppx: {uppx}\n'
+    #     f'xrange: {xrange}\n'
+    #     f'pxw: {pxw}\n'
+    #     f'frames: {frames}\n'
+    # )
+    assert frames >= (xrange / uppx)
 
     # call into ``numba``
     nb, i_win, y_out = _m4(
diff --git a/piker/ui/_cursor.py b/piker/ui/_cursor.py
index a34c15c1..606ff3f2 100644
--- a/piker/ui/_cursor.py
+++ b/piker/ui/_cursor.py
@@ -43,8 +43,8 @@ log = get_logger(__name__)
 # latency (in terms of perceived lag in cross hair) so really be sure
 # there's an improvement if you want to change it!
 
-_mouse_rate_limit = 120  # TODO; should we calc current screen refresh rate?
-_debounce_delay = 1 / 40
+_mouse_rate_limit = 60  # TODO; should we calc current screen refresh rate?
+_debounce_delay = 0
 _ch_label_opac = 1
 
 
@@ -98,25 +98,30 @@ class LineDot(pg.CurvePoint):
         ev: QtCore.QEvent,
 
     ) -> bool:
-        if not isinstance(
-            ev, QtCore.QDynamicPropertyChangeEvent
-        ) or self.curve() is None:
+
+        if (
+            not isinstance(ev, QtCore.QDynamicPropertyChangeEvent)
+            or self.curve() is None
+        ):
             return False
 
         # TODO: get rid of this ``.getData()`` and
         # make a more pythonic api to retreive backing
         # numpy arrays...
-        (x, y) = self.curve().getData()
-        index = self.property('index')
-        # first = self._plot._arrays['ohlc'][0]['index']
-        # first = x[0]
-        # i = index - first
-        if index:
-            i = round(index - x[0])
-            if i > 0 and i < len(y):
-                newPos = (index, y[i])
-                QtWidgets.QGraphicsItem.setPos(self, *newPos)
-                return True
+        # (x, y) = self.curve().getData()
+        # index = self.property('index')
+        # # first = self._plot._arrays['ohlc'][0]['index']
+        # # first = x[0]
+        # # i = index - first
+        # if index:
+        #     i = round(index - x[0])
+        #     if i > 0 and i < len(y):
+        #         newPos = (index, y[i])
+        #         QtWidgets.QGraphicsItem.setPos(
+        #             self,
+        #             *newPos,
+        #         )
+        #         return True
 
         return False
 
@@ -254,13 +259,13 @@ class ContentsLabels:
     def update_labels(
         self,
         index: int,
-        # array_name: str,
 
     ) -> None:
-        # for name, (label, update) in self._labels.items():
         for chart, name, label, update in self._labels:
 
-            array = chart._arrays[name]
+            flow = chart._flows[name]
+            array = flow.shm.array
+
             if not (
                 index >= 0
                 and index < array[-1]['index']
@@ -269,8 +274,6 @@ class ContentsLabels:
                 print('WTF out of range?')
                 continue
 
-            # array = chart._arrays[name]
-
             # call provided update func with data point
             try:
                 label.show()
@@ -472,9 +475,12 @@ class Cursor(pg.GraphicsObject):
     ) -> LineDot:
         # if this plot contains curves add line dot "cursors" to denote
         # the current sample under the mouse
+        main_flow = plot._flows[plot.name]
+        # read out last index
+        i = main_flow.shm.array[-1]['index']
         cursor = LineDot(
             curve,
-            index=plot._arrays[plot.name][-1]['index'],
+            index=i,
             plot=plot
         )
         plot.addItem(cursor)
diff --git a/piker/ui/_curve.py b/piker/ui/_curve.py
index 00a4ca7a..ac967bf7 100644
--- a/piker/ui/_curve.py
+++ b/piker/ui/_curve.py
@@ -18,83 +18,37 @@
 Fast, smooth, sexy curves.
 
 """
-from typing import Optional
+from contextlib import contextmanager as cm
+from typing import Optional, Callable
 
 import numpy as np
 import pyqtgraph as pg
-from PyQt5 import QtGui, QtWidgets
+from PyQt5 import QtWidgets
 from PyQt5.QtWidgets import QGraphicsItem
 from PyQt5.QtCore import (
     Qt,
     QLineF,
     QSizeF,
     QRectF,
+    # QRect,
     QPointF,
 )
-
+from PyQt5.QtGui import (
+    QPainter,
+    QPainterPath,
+)
 from .._profile import pg_profile_enabled, ms_slower_then
 from ._style import hcolor
-from ._compression import (
-    # ohlc_to_m4_line,
-    ds_m4,
-)
+# from ._compression import (
+#     # ohlc_to_m4_line,
+#     ds_m4,
+# )
 from ..log import get_logger
 
 
 log = get_logger(__name__)
 
 
-def step_path_arrays_from_1d(
-    x: np.ndarray,
-    y: np.ndarray,
-    include_endpoints: bool = False,
-
-) -> (np.ndarray, np.ndarray):
-    '''
-    Generate a "step mode" curve aligned with OHLC style bars
-    such that each segment spans each bar (aka "centered" style).
-
-    '''
-    y_out = y.copy()
-    x_out = x.copy()
-    x2 = np.empty(
-        # the data + 2 endpoints on either end for
-        # "termination of the path".
-        (len(x) + 1, 2),
-        # we want to align with OHLC or other sampling style
-        # bars likely so we need fractinal values
-        dtype=float,
-    )
-    x2[0] = x[0] - 0.5
-    x2[1] = x[0] + 0.5
-    x2[1:] = x[:, np.newaxis] + 0.5
-
-    # flatten to 1-d
-    x_out = x2.reshape(x2.size)
-
-    # we create a 1d with 2 extra indexes to
-    # hold the start and (current) end value for the steps
-    # on either end
-    y2 = np.empty((len(y), 2), dtype=y.dtype)
-    y2[:] = y[:, np.newaxis]
-
-    y_out = np.empty(
-        2*len(y) + 2,
-        dtype=y.dtype
-    )
-
-    # flatten and set 0 endpoints
-    y_out[1:-1] = y2.reshape(y2.size)
-    y_out[0] = 0
-    y_out[-1] = 0
-
-    if not include_endpoints:
-        return x_out[:-1], y_out[:-1]
-
-    else:
-        return x_out, y_out
-
-
 _line_styles: dict[str, int] = {
     'solid': Qt.PenStyle.SolidLine,
     'dash': Qt.PenStyle.DashLine,
@@ -103,24 +57,43 @@ _line_styles: dict[str, int] = {
 }
 
 
-class FastAppendCurve(pg.GraphicsObject):
+class Curve(pg.GraphicsObject):
     '''
-    A faster, append friendly version of ``pyqtgraph.PlotCurveItem``
-    built for real-time data updates.
+    A faster, simpler, append friendly version of
+    ``pyqtgraph.PlotCurveItem`` built for highly customizable real-time
+    updates.
 
-    The main difference is avoiding regeneration of the entire
-    historical path where possible and instead only updating the "new"
-    segment(s) via a ``numpy`` array diff calc. Further the "last"
-    graphic segment is drawn independently such that near-term (high
-    frequency) discrete-time-sampled style updates don't trigger a full
-    path redraw.
+    This type is a much stripped down version of a ``pyqtgraph`` style
+    "graphics object" in the sense that the internal lower level
+    graphics which are drawn in the ``.paint()`` method are actually
+    rendered outside of this class entirely and instead are assigned as
+    state (instance vars) here and then drawn during a Qt graphics
+    cycle.
+
+    The main motivation for this more modular, composed design is that
+    lower level graphics data can be rendered in different threads and
+    then read and drawn in this main thread without having to worry
+    about dealing with Qt's concurrency primitives. See
+    ``piker.ui._flows.Renderer`` for details and logic related to lower
+    level path generation and incremental update. The main differences in
+    the path generation code include:
+
+    - avoiding regeneration of the entire historical path where possible
+      and instead only updating the "new" segment(s) via a ``numpy``
+      array diff calc.
+    - here, the "last" graphics datum-segment is drawn independently
+      such that near-term (high frequency) discrete-time-sampled style
+      updates don't trigger a full path redraw.
 
     '''
+
+    # sub-type customization methods
+    sub_br: Optional[Callable] = None
+    sub_paint: Optional[Callable] = None
+    declare_paintables: Optional[Callable] = None
+
     def __init__(
         self,
-
-        x: np.ndarray,
-        y: np.ndarray,
         *args,
 
         step_mode: bool = False,
@@ -134,27 +107,25 @@ class FastAppendCurve(pg.GraphicsObject):
 
     ) -> None:
 
-        # brutaaalll, see comments within..
-        self._y = self.yData = y
-        self._x = self.xData = x
-
         self._name = name
-        self.path: Optional[QtGui.QPainterPath] = None
 
+        # brutaaalll, see comments within..
+        self.yData = None
+        self.xData = None
+
+        # self._last_cap: int = 0
+        self.path: Optional[QPainterPath] = None
+
+        # additional path used for appends which tries to avoid
+        # triggering an update/redraw of the presumably larger
+        # historical ``.path`` above.
         self.use_fpath = use_fpath
-        self.fast_path: Optional[QtGui.QPainterPath] = None
+        self.fast_path: Optional[QPainterPath] = None
 
         # TODO: we can probably just dispense with the parent since
         # we're basically only using the pen setting now...
         super().__init__(*args, **kwargs)
 
-        # self._xrange: tuple[int, int] = self.dataBounds(ax=0)
-        self._xrange: Optional[tuple[int, int]] = None
-
-        # self._last_draw = time.time()
-        self._in_ds: bool = False
-        self._last_uppx: float = 0
-
         # all history of curve is drawn in single px thickness
         pen = pg.mkPen(hcolor(color))
         pen.setStyle(_line_styles[style])
@@ -168,29 +139,43 @@ class FastAppendCurve(pg.GraphicsObject):
         # self.last_step_pen = pg.mkPen(hcolor(color), width=2)
         self.last_step_pen = pg.mkPen(pen, width=2)
 
-        self._last_line: Optional[QLineF] = None
-        self._last_step_rect: Optional[QRectF] = None
+        # self._last_line: Optional[QLineF] = None
+        self._last_line = QLineF()
+        self._last_w: float = 1
 
         # flat-top style histogram-like discrete curve
-        self._step_mode: bool = step_mode
+        # self._step_mode: bool = step_mode
 
         # self._fill = True
         self._brush = pg.functions.mkBrush(hcolor(fill_color or color))
 
+        # NOTE: this setting seems to mostly prevent redraws on mouse
+        # interaction which is a huge boon for avg interaction latency.
+
         # TODO: one question still remaining is if this makes trasform
         # interactions slower (such as zooming) and if so maybe if/when
         # we implement a "history" mode for the view we disable this in
         # that mode?
-        if step_mode:
-            # don't enable caching by default for the case where the
-            # only thing drawn is the "last" line segment which can
-            # have a weird artifact where it won't be fully drawn to its
-            # endpoint (something we saw on trade rate curves)
-            self.setCacheMode(
-                QGraphicsItem.DeviceCoordinateCache
-            )
+        # don't enable caching by default for the case where the
+        # only thing drawn is the "last" line segment which can
+        # have a weird artifact where it won't be fully drawn to its
+        # endpoint (something we saw on trade rate curves)
+        self.setCacheMode(QGraphicsItem.DeviceCoordinateCache)
 
-        self.update()
+        # XXX: see explanation for different caching modes:
+        # https://stackoverflow.com/a/39410081
+        # seems to only be useful if we don't re-generate the entire
+        # QPainterPath every time
+        # curve.setCacheMode(QtWidgets.QGraphicsItem.DeviceCoordinateCache)
+
+        # don't ever use this - it's a colossal nightmare of artefacts
+        # and is disastrous for performance.
+        # curve.setCacheMode(QtWidgets.QGraphicsItem.ItemCoordinateCache)
+
+        # allow sub-type customization
+        declare = self.declare_paintables
+        if declare:
+            declare()
 
     # TODO: probably stick this in a new parent
     # type which will contain our own version of
@@ -214,9 +199,6 @@ class FastAppendCurve(pg.GraphicsObject):
         vr = self.viewRect()
         l, r = int(vr.left()), int(vr.right())
 
-        if not self._xrange:
-            return 0
-
         start, stop = self._xrange
         lbar = max(l, start)
         rbar = min(r, stop)
@@ -225,352 +207,10 @@ class FastAppendCurve(pg.GraphicsObject):
             QLineF(lbar, 0, rbar, 0)
         ).length()
 
-    def downsample(
-        self,
-        x,
-        y,
-        px_width,
-        uppx,
-
-    ) -> tuple[np.ndarray, np.ndarray]:
-
-        # downsample whenever more then 1 pixels per datum can be shown.
-        # always refresh data bounds until we get diffing
-        # working properly, see above..
-        bins, x, y = ds_m4(
-            x,
-            y,
-            px_width=px_width,
-            uppx=uppx,
-            log_scale=bool(uppx)
-        )
-        x = np.broadcast_to(x[:, None], y.shape)
-        # x = (x + np.array([-0.43, 0, 0, 0.43])).flatten()
-        x = (x + np.array([-0.5, 0, 0, 0.5])).flatten()
-        y = y.flatten()
-
-        # presumably?
-        self._in_ds = True
-        return x, y
-
-    def update_from_array(
-        self,
-
-        # full array input history
-        x: np.ndarray,
-        y: np.ndarray,
-
-        # pre-sliced array data that's "in view"
-        x_iv: np.ndarray,
-        y_iv: np.ndarray,
-
-        view_range: Optional[tuple[int, int]] = None,
-        profiler: Optional[pg.debug.Profiler] = None,
-
-    ) -> QtGui.QPainterPath:
-        '''
-        Update curve from input 2-d data.
-
-        Compare with a cached "x-range" state and (pre/a)ppend based on
-        a length diff.
-
-        '''
-        profiler = profiler or pg.debug.Profiler(
-            msg=f'FastAppendCurve.update_from_array(): `{self._name}`',
-            disabled=not pg_profile_enabled(),
-            gt=ms_slower_then,
-        )
-        # flip_cache = False
-
-        if self._xrange:
-            istart, istop = self._xrange
-        else:
-            self._xrange = istart, istop = x[0], x[-1]
-        # print(f"xrange: {self._xrange}")
-
-        # XXX: lol brutal, the internals of `CurvePoint` (inherited by
-        # our `LineDot`) required ``.getData()`` to work..
-        self.xData = x
-        self.yData = y
-        self._x, self._y = x, y
-
-        if view_range:
-            profiler(f'view range slice {view_range}')
-
-        # downsampling incremental state checking
-        uppx = self.x_uppx()
-        px_width = self.px_width()
-        uppx_diff = (uppx - self._last_uppx)
-
-        should_ds = False
-        should_redraw = False
-
-        # if a view range is passed, plan to draw the
-        # source ouput that's "in view" of the chart.
-        if view_range and not self._in_ds:
-            # print(f'{self._name} vr: {view_range}')
-
-            # by default we only pull data up to the last (current) index
-            x_out, y_out = x_iv[:-1], y_iv[:-1]
-
-            # step mode: draw flat top discrete "step"
-            # over the index space for each datum.
-            if self._step_mode:
-                # TODO: numba this bish
-                x_out, y_out = step_path_arrays_from_1d(
-                    x_out,
-                    y_out
-                )
-                profiler('generated step arrays')
-
-            should_redraw = True
-            profiler('sliced in-view array history')
-
-            # x_last = x_iv[-1]
-            # y_last = y_iv[-1]
-            self._last_vr = view_range
-
-            # self.disable_cache()
-            # flip_cache = True
-
-        else:
-            self._xrange = x[0], x[-1]
-
-        x_last = x[-1]
-        y_last = y[-1]
-
-        # check for downsampling conditions
-        if (
-            # std m4 downsample conditions
-            px_width
-            and uppx_diff >= 4
-            or uppx_diff <= -3
-            or self._step_mode and abs(uppx_diff) >= 4
-
-        ):
-            log.info(
-                f'{self._name} sampler change: {self._last_uppx} -> {uppx}'
-            )
-            self._last_uppx = uppx
-            should_ds = True
-
-        elif (
-            uppx <= 2
-            and self._in_ds
-        ):
-            # we should de-downsample back to our original
-            # source data so we clear our path data in prep
-            # to generate a new one from original source data.
-            should_redraw = True
-            should_ds = False
-
-        # compute the length diffs between the first/last index entry in
-        # the input data and the last indexes we have on record from the
-        # last time we updated the curve index.
-        prepend_length = int(istart - x[0])
-        append_length = int(x[-1] - istop)
-
-        # no_path_yet = self.path is None
-        if (
-            self.path is None
-            or should_redraw
-            or should_ds
-            or prepend_length > 0
-        ):
-            if (
-                not view_range
-                or self._in_ds
-            ):
-                # by default we only pull data up to the last (current) index
-                x_out, y_out = x[:-1], y[:-1]
-
-                # step mode: draw flat top discrete "step"
-                # over the index space for each datum.
-                if self._step_mode:
-                    x_out, y_out = step_path_arrays_from_1d(
-                        x_out,
-                        y_out,
-                    )
-                    # TODO: numba this bish
-                    profiler('generated step arrays')
-
-            if should_redraw:
-                profiler('path reversion to non-ds')
-                if self.path:
-                    self.path.clear()
-
-                if self.fast_path:
-                    self.fast_path.clear()
-
-            if should_redraw and not should_ds:
-                if self._in_ds:
-                    log.info(f'DEDOWN -> {self._name}')
-
-                self._in_ds = False
-
-            elif should_ds and px_width:
-                x_out, y_out = self.downsample(
-                    x_out,
-                    y_out,
-                    px_width,
-                    uppx,
-                )
-                profiler(f'FULL PATH downsample redraw={should_ds}')
-                self._in_ds = True
-
-            self.path = pg.functions.arrayToQPath(
-                x_out,
-                y_out,
-                connect='all',
-                finiteCheck=False,
-                path=self.path,
-            )
-            profiler('generated fresh path')
-            # profiler(f'DRAW PATH IN VIEW -> {self._name}')
-
-            # reserve mem allocs see:
-            # - https://doc.qt.io/qt-5/qpainterpath.html#reserve
-            # - https://doc.qt.io/qt-5/qpainterpath.html#capacity
-            # - https://doc.qt.io/qt-5/qpainterpath.html#clear
-            # XXX: right now this is based on had hoc checks on a
-            # hidpi 3840x2160 4k monitor but we should optimize for
-            # the target display(s) on the sys.
-            # if no_path_yet:
-            #     self.path.reserve(int(500e3))
-
-        # TODO: get this piecewise prepend working - right now it's
-        # giving heck on vwap...
-        # elif prepend_length:
-        #     breakpoint()
-
-        #     prepend_path = pg.functions.arrayToQPath(
-        #         x[0:prepend_length],
-        #         y[0:prepend_length],
-        #         connect='all'
-        #     )
-
-        #     # swap prepend path in "front"
-        #     old_path = self.path
-        #     self.path = prepend_path
-        #     # self.path.moveTo(new_x[0], new_y[0])
-        #     self.path.connectPath(old_path)
-
-        elif (
-            append_length > 0
-            and not view_range
-        ):
-            new_x = x[-append_length - 2:-1]
-            new_y = y[-append_length - 2:-1]
-
-            if self._step_mode:
-                new_x, new_y = step_path_arrays_from_1d(
-                    new_x,
-                    new_y,
-                )
-                # [1:] since we don't need the vertical line normally at
-                # the beginning of the step curve taking the first (x,
-                # y) poing down to the x-axis **because** this is an
-                # appended path graphic.
-                new_x = new_x[1:]
-                new_y = new_y[1:]
-
-            profiler('diffed append arrays')
-
-            if should_ds:
-                new_x, new_y = self.downsample(
-                    new_x,
-                    new_y,
-                    **should_ds,
-                )
-                profiler(f'fast path downsample redraw={should_ds}')
-
-            append_path = pg.functions.arrayToQPath(
-                new_x,
-                new_y,
-                connect='all',
-                finiteCheck=False,
-                path=self.fast_path,
-            )
-
-            if self.use_fpath:
-                # an attempt at trying to make append-updates faster..
-                if self.fast_path is None:
-                    self.fast_path = append_path
-                    self.fast_path.reserve(int(6e3))
-                else:
-                    self.fast_path.connectPath(append_path)
-                    size = self.fast_path.capacity()
-                    profiler(f'connected fast path w size: {size}')
-
-                    # print(f"append_path br: {append_path.boundingRect()}")
-                    # self.path.moveTo(new_x[0], new_y[0])
-                    # path.connectPath(append_path)
-
-                    # XXX: lol this causes a hang..
-                    # self.path = self.path.simplified()
-            else:
-                size = self.path.capacity()
-                profiler(f'connected history path w size: {size}')
-                self.path.connectPath(append_path)
-
-            # other merging ideas:
-            # https://stackoverflow.com/questions/8936225/how-to-merge-qpainterpaths
-            # path.addPath(append_path)
-            # path.closeSubpath()
-
-            # TODO: try out new work from `pyqtgraph` main which
-            # should repair horrid perf:
-            # https://github.com/pyqtgraph/pyqtgraph/pull/2032
-            # ok, nope still horrible XD
-            # if self._fill:
-            #     # XXX: super slow set "union" op
-            #     self.path = self.path.united(append_path).simplified()
-
-            # self.disable_cache()
-            # flip_cache = True
-
-        # draw the "current" step graphic segment so it lines up with
-        # the "middle" of the current (OHLC) sample.
-        if self._step_mode:
-            self._last_line = QLineF(
-                x_last - 0.5, 0,
-                x_last + 0.5, 0,
-            )
-            self._last_step_rect = QRectF(
-                x_last - 0.5, 0,
-                x_last + 0.5, y_last
-            )
-            # print(
-            #     f"path br: {self.path.boundingRect()}",
-            #     f"fast path br: {self.fast_path.boundingRect()}",
-            #     f"last rect br: {self._last_step_rect}",
-            # )
-        else:
-            self._last_line = QLineF(
-                x[-2], y[-2],
-                x[-1], y_last
-            )
-
-        profiler('draw last segment')
-
-        # trigger redraw of path
-        # do update before reverting to cache mode
-        # self.prepareGeometryChange()
-        self.update()
-        profiler('.update()')
-
-        # if flip_cache:
-        #     # XXX: seems to be needed to avoid artifacts (see above).
-        #     self.setCacheMode(QGraphicsItem.DeviceCoordinateCache)
-
     # XXX: lol brutal, the internals of `CurvePoint` (inherited by
     # our `LineDot`) required ``.getData()`` to work..
     def getData(self):
-        return self._x, self._y
-
-    # TODO: drop the above after ``Cursor`` re-work
-    def get_arrays(self) -> tuple[np.ndarray, np.ndarray]:
-        return self._x, self._y
+        return self.xData, self.yData
 
     def clear(self):
         '''
@@ -593,25 +233,18 @@ class FastAppendCurve(pg.GraphicsObject):
                 # self.fast_path.clear()
                 self.fast_path = None
 
-        # self.disable_cache()
-        # self.setCacheMode(QGraphicsItem.DeviceCoordinateCache)
-
-    def disable_cache(self) -> None:
-        '''
-        Disable the use of the pixel coordinate cache and trigger a geo event.
-
-        '''
-        # XXX: pretty annoying but, without this there's little
-        # artefacts on the append updates to the curve...
+    @cm
+    def reset_cache(self) -> None:
         self.setCacheMode(QtWidgets.QGraphicsItem.NoCache)
-        self.prepareGeometryChange()
+        yield
+        self.setCacheMode(QGraphicsItem.DeviceCoordinateCache)
 
     def boundingRect(self):
         '''
         Compute and then cache our rect.
         '''
         if self.path is None:
-            return QtGui.QPainterPath().boundingRect()
+            return QPainterPath().boundingRect()
         else:
             # dynamically override this method after initial
             # path is created to avoid requiring the above None check
@@ -623,6 +256,7 @@ class FastAppendCurve(pg.GraphicsObject):
         Post init ``.boundingRect()```.
 
         '''
+        # hb = self.path.boundingRect()
         hb = self.path.controlPointRect()
         hb_size = hb.size()
 
@@ -630,17 +264,60 @@ class FastAppendCurve(pg.GraphicsObject):
         if fp:
             fhb = fp.controlPointRect()
             hb_size = fhb.size() + hb_size
+
         # print(f'hb_size: {hb_size}')
 
-        w = hb_size.width() + 1
-        h = hb_size.height() + 1
+        # if self._last_step_rect:
+        #     hb_size += self._last_step_rect.size()
+
+        # if self._line:
+        #     br = self._last_step_rect.bottomRight()
+
+        # tl = QPointF(
+        #     # self._vr[0],
+        #     # hb.topLeft().y(),
+        #     # 0,
+        #     # hb_size.height() + 1
+        # )
+
+        #     br = self._last_step_rect.bottomRight()
+
+        w = hb_size.width()
+        h = hb_size.height()
+
+        sbr = self.sub_br
+        if sbr:
+            w, h = self.sub_br(w, h)
+        else:
+            # assume plain line graphic and use
+            # default unit step in each direction.
+
+            # only on a plane line do we include
+            # and extra index step's worth of width
+            # since in the step case the end of the curve
+            # actually terminates earlier so we don't need
+            # this for the last step.
+            w += self._last_w
+            # ll = self._last_line
+            h += 1  # ll.y2() - ll.y1()
+
+        # br = QPointF(
+        #     self._vr[-1],
+        #     # tl.x() + w,
+        #     tl.y() + h,
+        # )
 
         br = QRectF(
 
             # top left
+            # hb.topLeft()
+            # tl,
             QPointF(hb.topLeft()),
 
+            # br,
             # total size
+            # QSizeF(hb_size)
+            # hb_size,
             QSizeF(w, h)
         )
         # print(f'bounding rect: {br}')
@@ -648,40 +325,36 @@ class FastAppendCurve(pg.GraphicsObject):
 
     def paint(
         self,
-        p: QtGui.QPainter,
+        p: QPainter,
         opt: QtWidgets.QStyleOptionGraphicsItem,
         w: QtWidgets.QWidget
 
     ) -> None:
 
         profiler = pg.debug.Profiler(
-            msg=f'FastAppendCurve.paint(): `{self._name}`',
+            msg=f'Curve.paint(): `{self._name}`',
             disabled=not pg_profile_enabled(),
-            gt=ms_slower_then,
+            ms_threshold=ms_slower_then,
         )
 
-        if (
-            self._step_mode
-            and self._last_step_rect
-        ):
-            brush = self._brush
+        sub_paint = self.sub_paint
+        if sub_paint:
+            sub_paint(p, profiler)
 
-            # p.drawLines(*tuple(filter(bool, self._last_step_lines)))
-            # p.drawRect(self._last_step_rect)
-            p.fillRect(self._last_step_rect, brush)
-            profiler('.fillRect()')
-
-        if self._last_line:
-            p.setPen(self.last_step_pen)
-            p.drawLine(self._last_line)
-            profiler('.drawLine()')
-            p.setPen(self._pen)
+        p.setPen(self.last_step_pen)
+        p.drawLine(self._last_line)
+        profiler('.drawLine()')
+        p.setPen(self._pen)
 
         path = self.path
+        # cap = path.capacity()
+        # if cap != self._last_cap:
+        #     print(f'NEW CAPACITY: {self._last_cap} -> {cap}')
+        #     self._last_cap = cap
 
         if path:
             p.drawPath(path)
-            profiler('.drawPath(path)')
+            profiler(f'.drawPath(path): {path.capacity()}')
 
         fp = self.fast_path
         if fp:
@@ -695,3 +368,117 @@ class FastAppendCurve(pg.GraphicsObject):
         # if self._fill:
         #     brush = self.opts['brush']
         #     p.fillPath(self.path, brush)
+
+    def draw_last_datum(
+        self,
+        path: QPainterPath,
+        src_data: np.ndarray,
+        render_data: np.ndarray,
+        reset: bool,
+        array_key: str,
+
+    ) -> None:
+        # default line draw last call
+        with self.reset_cache():
+            x = render_data['index']
+            y = render_data[array_key]
+
+            # draw the "current" step graphic segment so it
+            # lines up with the "middle" of the current
+            # (OHLC) sample.
+            self._last_line = QLineF(
+                x[-2], y[-2],
+                x[-1], y[-1],
+            )
+
+        return x, y
+
+
+# TODO: this should probably be a "downsampled" curve type
+# that draws a bar-style (but for the px column) last graphics
+# element such that the current datum in view can be shown
+# (via it's max / min) even when highly zoomed out.
+class FlattenedOHLC(Curve):
+
+    def draw_last_datum(
+        self,
+        path: QPainterPath,
+        src_data: np.ndarray,
+        render_data: np.ndarray,
+        reset: bool,
+        array_key: str,
+
+    ) -> None:
+        lasts = src_data[-2:]
+        x = lasts['index']
+        y = lasts['close']
+
+        # draw the "current" step graphic segment so it
+        # lines up with the "middle" of the current
+        # (OHLC) sample.
+        self._last_line = QLineF(
+            x[-2], y[-2],
+            x[-1], y[-1]
+        )
+        return x, y
+
+
+class StepCurve(Curve):
+
+    def declare_paintables(
+        self,
+    ) -> None:
+        self._last_step_rect = QRectF()
+
+    def draw_last_datum(
+        self,
+        path: QPainterPath,
+        src_data: np.ndarray,
+        render_data: np.ndarray,
+        reset: bool,
+        array_key: str,
+
+        w: float = 0.5,
+
+    ) -> None:
+
+        # TODO: remove this and instead place all step curve
+        # updating into pre-path data render callbacks.
+        # full input data
+        x = src_data['index']
+        y = src_data[array_key]
+
+        x_last = x[-1]
+        y_last = y[-1]
+
+        # lol, commenting this makes step curves
+        # all "black" for me :eyeroll:..
+        self._last_line = QLineF(
+            x_last - w, 0,
+            x_last + w, 0,
+        )
+        self._last_step_rect = QRectF(
+            x_last - w, 0,
+            x_last + w, y_last,
+        )
+        return x, y
+
+    def sub_paint(
+        self,
+        p: QPainter,
+        profiler: pg.debug.Profiler,
+
+    ) -> None:
+        # p.drawLines(*tuple(filter(bool, self._last_step_lines)))
+        # p.drawRect(self._last_step_rect)
+        p.fillRect(self._last_step_rect, self._brush)
+        profiler('.fillRect()')
+
+    def sub_br(
+        self,
+        path_w: float,
+        path_h: float,
+
+    ) -> (float, float):
+        # passthrough
+        return path_w, path_h
diff --git a/piker/ui/_display.py b/piker/ui/_display.py
index 927ce5df..415827fb 100644
--- a/piker/ui/_display.py
+++ b/piker/ui/_display.py
@@ -32,7 +32,7 @@ import trio
 import pendulum
 import pyqtgraph as pg
 
-from .. import brokers
+# from .. import brokers
 from ..data.feed import open_feed
 from ._axes import YAxisLabel
 from ._chart import (
@@ -54,16 +54,16 @@ from ._forms import (
     mk_order_pane_layout,
 )
 from .order_mode import open_order_mode
-# from .._profile import (
-#     pg_profile_enabled,
-#     ms_slower_then,
-# )
+from .._profile import (
+    pg_profile_enabled,
+    ms_slower_then,
+)
 from ..log import get_logger
 
 log = get_logger(__name__)
 
 # TODO: load this from a config.toml!
-_quote_throttle_rate: int = 12  # Hz
+_quote_throttle_rate: int = 22  # Hz
 
 
 # a working tick-type-classes template
@@ -96,28 +96,19 @@ def chart_maxmin(
     Compute max and min datums "in view" for range limits.
 
     '''
-    array = ohlcv_shm.array
-    ifirst = array[0]['index']
-
     last_bars_range = chart.bars_range()
-    l, lbar, rbar, r = last_bars_range
-    in_view = array[lbar - ifirst:rbar - ifirst + 1]
+    out = chart.maxmin()
 
-    if not in_view.size:
-        log.warning('Resetting chart to data')
-        chart.default_view()
+    if out is None:
         return (last_bars_range, 0, 0, 0)
 
-    mx, mn = (
-        np.nanmax(in_view['high']),
-        np.nanmin(in_view['low'],)
-    )
+    mn, mx = out
 
     mx_vlm_in_view = 0
     if vlm_chart:
-        mx_vlm_in_view = np.max(
-            in_view['volume']
-        )
+        out = vlm_chart.maxmin()
+        if out:
+            _, mx_vlm_in_view = out
 
     return (
         last_bars_range,
@@ -272,6 +263,7 @@ async def graphics_update_loop(
         'vars': {
             'tick_margin': tick_margin,
             'i_last': i_last,
+            'i_last_append': i_last,
             'last_mx_vlm': last_mx_vlm,
             'last_mx': last_mx,
             'last_mn': last_mn,
@@ -318,6 +310,7 @@ def graphics_update_cycle(
     ds: DisplayState,
     wap_in_history: bool = False,
     trigger_all: bool = False,  # flag used by prepend history updates
+    prepend_update_index: Optional[int] = None,
 
 ) -> None:
     # TODO: eventually optimize this whole graphics stack with ``numba``
@@ -327,9 +320,12 @@ def graphics_update_cycle(
 
     profiler = pg.debug.Profiler(
         msg=f'Graphics loop cycle for: `{chart.name}`',
-        disabled=True,  # not pg_profile_enabled(),
-        gt=1/12 * 1e3,
-        # gt=ms_slower_then,
+        delayed=True,
+        disabled=not pg_profile_enabled(),
+        # disabled=True,
+        ms_threshold=ms_slower_then,
+
+        # ms_threshold=1/12 * 1e3,
     )
 
     # unpack multi-referenced components
@@ -340,12 +336,12 @@ def graphics_update_cycle(
     vars = ds.vars
     tick_margin = vars['tick_margin']
 
-    update_uppx = 6
+    update_uppx = 16
 
     for sym, quote in ds.quotes.items():
 
         # compute the first available graphic's x-units-per-pixel
-        xpx = vlm_chart.view.x_uppx()
+        uppx = vlm_chart.view.x_uppx()
 
         # NOTE: vlm may be written by the ``brokerd`` backend
         # event though a tick sample is not emitted.
@@ -364,26 +360,58 @@ def graphics_update_cycle(
         i_diff = i_step - vars['i_last']
         vars['i_last'] = i_step
 
+        append_diff = i_step - vars['i_last_append']
+
+        # update the "last datum" (aka extending the flow graphic with
+        # new data) only if the number of unit steps is >= the number of
+        # such unit steps per pixel (aka uppx). Iow, if the zoom level
+        # is such that a datum(s) update to graphics wouldn't span
+        # to a new pixel, we don't update yet.
+        do_append = (append_diff >= uppx)
+        if do_append:
+            vars['i_last_append'] = i_step
+
+        do_rt_update = uppx < update_uppx
+        # print(
+        #     f'append_diff:{append_diff}\n'
+        #     f'uppx:{uppx}\n'
+        #     f'do_append: {do_append}'
+        # )
+
+        # TODO: we should only run mxmn when we know
+        # an update is due via ``do_append`` above.
         (
             brange,
             mx_in_view,
             mn_in_view,
             mx_vlm_in_view,
         ) = ds.maxmin()
-
         l, lbar, rbar, r = brange
         mx = mx_in_view + tick_margin
         mn = mn_in_view - tick_margin
-        profiler('maxmin call')
-        liv = r > i_step  # the last datum is in view
+
+        profiler('`ds.maxmin()` call')
+
+        liv = r >= i_step  # the last datum is in view
+
+        if (
+            prepend_update_index is not None
+            and lbar > prepend_update_index
+        ):
+            # on a history update (usually from the FSP subsys)
+            # if the segment of history that is being prepended
+            # isn't in view there is no reason to do a graphics
+            # update.
+            log.debug('Skipping prepend graphics cycle: frame not in view')
+            return
 
         # don't real-time "shift" the curve to the
         # left unless we get one of the following:
         if (
             (
-                i_diff > 0  # no new sample step
-                and xpx < 4  # chart is zoomed out very far
-                and r >= i_step  # the last datum isn't in view
+                # i_diff > 0  # no new sample step
+                do_append
+                # and uppx < 4  # chart is zoomed out very far
                 and liv
             )
             or trigger_all
@@ -393,6 +421,11 @@ def graphics_update_cycle(
             # and then iff update curves and shift?
             chart.increment_view(steps=i_diff)
 
+            if vlm_chart:
+                vlm_chart.increment_view(steps=i_diff)
+
+            profiler('view incremented')
+
         if vlm_chart:
             # always update y-label
             ds.vlm_sticky.update_from_data(
@@ -401,17 +434,16 @@ def graphics_update_cycle(
 
             if (
                 (
-                    xpx < update_uppx or i_diff > 0
+                    do_rt_update
+                    or do_append
                     and liv
                 )
                 or trigger_all
             ):
                 # TODO: make it so this doesn't have to be called
                 # once the $vlm is up?
-                vlm_chart.update_graphics_from_array(
+                vlm_chart.update_graphics_from_flow(
                     'volume',
-                    array,
-
                     # UGGGh, see ``maxmin()`` impl in `._fsp` for
                     # the overlayed plotitems... we need a better
                     # bay to invoke a maxmin per overlay..
@@ -424,6 +456,7 @@ def graphics_update_cycle(
                     # connected to update accompanying overlay
                     # graphics..
                 )
+                profiler('`vlm_chart.update_graphics_from_flow()`')
 
                 if (
                     mx_vlm_in_view != vars['last_mx_vlm']
@@ -432,22 +465,29 @@ def graphics_update_cycle(
                     vlm_chart.view._set_yrange(
                         yrange=yrange,
                     )
+                    profiler('`vlm_chart.view._set_yrange()`')
                     # print(f'mx vlm: {last_mx_vlm} -> {mx_vlm_in_view}')
                     vars['last_mx_vlm'] = mx_vlm_in_view
 
                 for curve_name, flow in vlm_chart._flows.items():
+
+                    if not flow.render:
+                        continue
+
                     update_fsp_chart(
                         vlm_chart,
                         flow,
                         curve_name,
                         array_key=curve_name,
+                        # do_append=uppx < update_uppx,
+                        do_append=do_append,
                     )
                     # is this even doing anything?
                     # (pretty sure it's the real-time
                     # resizing from last quote?)
                     fvb = flow.plot.vb
                     fvb._set_yrange(
-                        autoscale_linked_plots=False,
+                        # autoscale_linked_plots=False,
                         name=curve_name,
                     )
 
@@ -496,13 +536,17 @@ def graphics_update_cycle(
 
         # update ohlc sampled price bars
         if (
-            xpx < update_uppx
-            or i_diff > 0
+            do_rt_update
+            or do_append
             or trigger_all
         ):
-            chart.update_graphics_from_array(
+            # TODO: we should always update the "last" datum
+            # since the current range should at least be updated
+            # to it's max/min on the last pixel.
+            chart.update_graphics_from_flow(
                 chart.name,
-                array,
+                # do_append=uppx < update_uppx,
+                do_append=do_append,
             )
 
         # iterate in FIFO order per tick-frame
@@ -515,8 +559,9 @@ def graphics_update_cycle(
             # tick frames to determine the y-range for chart
             # auto-scaling.
             # TODO: we need a streaming minmax algo here, see def above.
-            mx = max(price + tick_margin, mx)
-            mn = min(price - tick_margin, mn)
+            if liv:
+                mx = max(price + tick_margin, mx)
+                mn = min(price - tick_margin, mn)
 
             if typ in clear_types:
 
@@ -539,9 +584,8 @@ def graphics_update_cycle(
 
                 if wap_in_history:
                     # update vwap overlay line
-                    chart.update_graphics_from_array(
+                    chart.update_graphics_from_flow(
                         'bar_wap',
-                        array,
                     )
 
             # L1 book label-line updates
@@ -557,7 +601,7 @@ def graphics_update_cycle(
 
                 if (
                     label is not None
-                    # and liv
+                    and liv
                 ):
                     label.update_fields(
                         {'level': price, 'size': size}
@@ -571,7 +615,7 @@ def graphics_update_cycle(
                 typ in _tick_groups['asks']
                 # TODO: instead we could check if the price is in the
                 # y-view-range?
-                # and liv
+                and liv
             ):
                 l1.ask_label.update_fields({'level': price, 'size': size})
 
@@ -579,7 +623,7 @@ def graphics_update_cycle(
                 typ in _tick_groups['bids']
                 # TODO: instead we could check if the price is in the
                 # y-view-range?
-                # and liv
+                and liv
             ):
                 l1.bid_label.update_fields({'level': price, 'size': size})
 
@@ -594,6 +638,7 @@ def graphics_update_cycle(
                 main_vb._ic is None
                 or not main_vb._ic.is_set()
             ):
+                # print(f'updating range due to mxmn')
                 main_vb._set_yrange(
                     # TODO: we should probably scale
                     # the view margin based on the size
@@ -604,10 +649,24 @@ def graphics_update_cycle(
                     yrange=(mn, mx),
                 )
 
-            vars['last_mx'], vars['last_mn'] = mx, mn
+        # XXX: update this every draw cycle to make L1-always-in-view work.
+        vars['last_mx'], vars['last_mn'] = mx, mn
 
         # run synchronous update on all linked flows
         for curve_name, flow in chart._flows.items():
+
+            if (
+                not (do_rt_update or do_append)
+                and liv
+                # even if we're downsampled bigly
+                # draw the last datum in the final
+                # px column to give the user the mx/mn
+                # range of that set.
+            ):
+                # always update the last datum-element
+                # graphic for all flows
+                flow.draw_last(array_key=curve_name)
+
             # TODO: should the "main" (aka source) flow be special?
             if curve_name == chart.data_key:
                 continue
@@ -643,7 +702,7 @@ async def display_symbol_data(
     )
 
     # historical data fetch
-    brokermod = brokers.get_brokermod(provider)
+    # brokermod = brokers.get_brokermod(provider)
 
     # ohlc_status_done = sbar.open_status(
     #     'retreiving OHLC history.. ',
@@ -692,32 +751,31 @@ async def display_symbol_data(
         # create main OHLC chart
         chart = linked.plot_ohlc_main(
             symbol,
-            bars,
+            ohlcv,
             sidepane=pp_pane,
         )
+        chart.default_view()
         chart._feeds[symbol.key] = feed
         chart.setFocus()
 
         # plot historical vwap if available
         wap_in_history = False
 
-        if brokermod._show_wap_in_history:
+        # XXX: FOR SOME REASON THIS IS CAUSING HANGZ!?!
+        # if brokermod._show_wap_in_history:
 
-            if 'bar_wap' in bars.dtype.fields:
-                wap_in_history = True
-                chart.draw_curve(
-                    name='bar_wap',
-                    data=bars,
-                    add_label=False,
-                )
+        #     if 'bar_wap' in bars.dtype.fields:
+        #         wap_in_history = True
+        #         chart.draw_curve(
+        #             name='bar_wap',
+        #             shm=ohlcv,
+        #             color='default_light',
+        #             add_label=False,
+        #         )
 
         # size view to data once at outset
         chart.cv._set_yrange()
 
-        # TODO: a data view api that makes this less shit
-        chart._shm = ohlcv
-        chart._flows[chart.data_key].shm = ohlcv
-
         # NOTE: we must immediately tell Qt to show the OHLC chart
         # to avoid a race where the subplots get added/shown to
         # the linked set *before* the main price chart!
@@ -780,6 +838,5 @@ async def display_symbol_data(
                 sbar._status_groups[loading_sym_key][1]()
 
                 # let the app run.. bby
-                chart.default_view()
                 # linked.graphics_cycle()
                 await trio.sleep_forever()
diff --git a/piker/ui/_editors.py b/piker/ui/_editors.py
index 9a99d2f7..03fd208e 100644
--- a/piker/ui/_editors.py
+++ b/piker/ui/_editors.py
@@ -343,7 +343,7 @@ class SelectRect(QtGui.QGraphicsRectItem):
         nbars = ixmx - ixmn + 1
 
         chart = self._chart
-        data = chart._arrays[chart.name][ixmn:ixmx]
+        data = chart._flows[chart.name].shm.array[ixmn:ixmx]
 
         if len(data):
             std = data['close'].std()
diff --git a/piker/ui/_exec.py b/piker/ui/_exec.py
index 7b69acef..1d1a9c3d 100644
--- a/piker/ui/_exec.py
+++ b/piker/ui/_exec.py
@@ -49,10 +49,6 @@ from . import _style
 log = get_logger(__name__)
 
 # pyqtgraph global config
-# might as well enable this for now?
-pg.useOpenGL = True
-pg.enableExperimental = True
-
 # engage core tweaks that give us better response
 # latency then the average pg user
 _do_overrides()
diff --git a/piker/ui/_flows.py b/piker/ui/_flows.py
new file mode 100644
index 00000000..01bbbece
--- /dev/null
+++ b/piker/ui/_flows.py
@@ -0,0 +1,1204 @@
+# piker: trading gear for hackers
+# Copyright (C) Tyler Goodlet (in stewardship for pikers)
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+'''
+High level streaming graphics primitives.
+
+This is an intermediate layer which associates real-time low latency
+graphics primitives with underlying FSP related data structures for fast
+incremental update.
+
+'''
+from __future__ import annotations
+from typing import (
+    Optional,
+    Callable,
+    Union,
+)
+
+import msgspec
+import numpy as np
+from numpy.lib import recfunctions as rfn
+import pyqtgraph as pg
+from PyQt5.QtGui import QPainterPath
+from PyQt5.QtCore import QLineF
+
+from ..data._sharedmem import (
+    ShmArray,
+)
+from .._profile import (
+    pg_profile_enabled,
+    # ms_slower_then,
+)
+from ._pathops import (
+    gen_ohlc_qpath,
+    ohlc_to_line,
+    to_step_format,
+    xy_downsample,
+)
+from ._ohlc import (
+    BarItems,
+    # bar_from_ohlc_row,
+)
+from ._curve import (
+    Curve,
+    StepCurve,
+    FlattenedOHLC,
+)
+from ..log import get_logger
+
+
+log = get_logger(__name__)
+
+
+# class FlowsTable(msgspec.Struct):
+#     '''
+#     Data-AGGRegate: high level API onto multiple (categorized)
+#     ``Flow``s with high level processing routines for
+#     multi-graphics computations and display.
+
+#     '''
+#     flows: dict[str, np.ndarray] = {}
+
+
+def update_ohlc_to_line(
+    src_shm: ShmArray,
+    array_key: str,
+    src_update: np.ndarray,
+    slc: slice,
+    ln: int,
+    first: int,
+    last: int,
+    is_append: bool,
+
+) -> np.ndarray:
+
+    fields = ['open', 'high', 'low', 'close']
+    return (
+        rfn.structured_to_unstructured(src_update[fields]),
+        slc,
+    )
+
+
+def ohlc_flat_to_xy(
+    r: Renderer,
+    array: np.ndarray,
+    array_key: str,
+    vr: tuple[int, int],
+
+) -> tuple[
+    np.ndarray,
+    np.nd.array,
+    str,
+]:
+    # TODO: in the case of an existing ``.update_xy()``
+    # should we be passing in array as an xy arrays tuple?
+
+    # 2 more datum-indexes to capture zero at end
+    x_flat = r.x_data[r._xy_first:r._xy_last]
+    y_flat = r.y_data[r._xy_first:r._xy_last]
+
+    # slice to view
+    ivl, ivr = vr
+    x_iv_flat = x_flat[ivl:ivr]
+    y_iv_flat = y_flat[ivl:ivr]
+
+    # reshape to 1d for graphics rendering
+    y_iv = y_iv_flat.reshape(-1)
+    x_iv = x_iv_flat.reshape(-1)
+
+    return x_iv, y_iv, 'all'
+
+
+def render_baritems(
+    flow: Flow,
+    graphics: BarItems,
+    read: tuple[
+        int, int, np.ndarray,
+        int, int, np.ndarray,
+    ],
+    profiler: pg.debug.Profiler,
+    **kwargs,
+
+) -> None:
+    '''
+    Graphics management logic for a ``BarItems`` object.
+
+    Mostly just logic to determine when and how to downsample an OHLC
+    lines curve into a flattened line graphic and when to display one
+    graphic or the other.
+
+    TODO: this should likely be moved into some kind of better abstraction
+    layer, if not a `Renderer` then something just above it?
+
+    '''
+    bars = graphics
+
+    # if no source data renderer exists create one.
+    self = flow
+    show_bars: bool = False
+
+    r = self._src_r
+    if not r:
+        show_bars = True
+        # OHLC bars path renderer
+        r = self._src_r = Renderer(
+            flow=self,
+            format_xy=gen_ohlc_qpath,
+            last_read=read,
+        )
+
+        ds_curve_r = Renderer(
+            flow=self,
+            last_read=read,
+
+            # incr update routines
+            allocate_xy=ohlc_to_line,
+            update_xy=update_ohlc_to_line,
+            format_xy=ohlc_flat_to_xy,
+        )
+
+        curve = FlattenedOHLC(
+            name=f'{flow.name}_ds_ohlc',
+            color=bars._color,
+        )
+        curve.hide()
+        self.plot.addItem(curve)
+
+        # baseline "line" downsampled OHLC curve that should
+        # kick on only when we reach a certain uppx threshold.
+        self._render_table = (ds_curve_r, curve)
+
+    ds_r, curve = self._render_table
+
+    # do checks for whether or not we require downsampling:
+    # - if we're **not** downsampling then we simply want to
+    #   render the bars graphics curve and update..
+    # - if instead we are in a downsamplig state then we to
+    x_gt = 6
+    uppx = curve.x_uppx()
+    in_line = should_line = curve.isVisible()
+    if (
+        should_line
+        and uppx < x_gt
+    ):
+        # print('FLIPPING TO BARS')
+        should_line = False
+
+    elif (
+        not should_line
+        and uppx >= x_gt
+    ):
+        # print('FLIPPING TO LINE')
+        should_line = True
+
+    profiler(f'ds logic complete line={should_line}')
+
+    # do graphics updates
+    if should_line:
+        r = ds_r
+        graphics = curve
+        profiler('updated ds curve')
+
+    else:
+        graphics = bars
+
+    if show_bars:
+        bars.show()
+
+    changed_to_line = False
+    if (
+        not in_line
+        and should_line
+    ):
+        # change to line graphic
+        log.info(
+            f'downsampling to line graphic {self.name}'
+        )
+        bars.hide()
+        curve.show()
+        curve.update()
+        changed_to_line = True
+
+    elif in_line and not should_line:
+        # change to bars graphic
+        log.info(f'showing bars graphic {self.name}')
+        curve.hide()
+        bars.show()
+        bars.update()
+
+    return (
+        graphics,
+        r,
+        {'read_from_key': False},
+        should_line,
+        changed_to_line,
+    )
+
+
+def update_step_xy(
+    src_shm: ShmArray,
+    array_key: str,
+    y_update: np.ndarray,
+    slc: slice,
+    ln: int,
+    first: int,
+    last: int,
+    is_append: bool,
+
+) -> np.ndarray:
+
+    # for a step curve we slice from one datum prior
+    # to the current "update slice" to get the previous
+    # "level".
+    if is_append:
+        start = max(last - 1, 0)
+        end = src_shm._last.value
+        new_y = src_shm._array[start:end][array_key]
+        slc = slice(start, end)
+
+    else:
+        new_y = y_update
+
+    return (
+        np.broadcast_to(
+            new_y[:, None], (new_y.size, 2),
+        ),
+        slc,
+    )
+
+
+def step_to_xy(
+    r: Renderer,
+    array: np.ndarray,
+    array_key: str,
+    vr: tuple[int, int],
+
+) -> tuple[
+    np.ndarray,
+    np.nd.array,
+    str,
+]:
+
+    # 2 more datum-indexes to capture zero at end
+    x_step = r.x_data[r._xy_first:r._xy_last+2]
+    y_step = r.y_data[r._xy_first:r._xy_last+2]
+
+    lasts = array[['index', array_key]]
+    last = lasts[array_key][-1]
+    y_step[-1] = last
+
+    # slice out in-view data
+    ivl, ivr = vr
+    ys_iv = y_step[ivl:ivr+1]
+    xs_iv = x_step[ivl:ivr+1]
+
+    # flatten to 1d
+    y_iv = ys_iv.reshape(ys_iv.size)
+    x_iv = xs_iv.reshape(xs_iv.size)
+
+    # print(
+    #     f'ys_iv : {ys_iv[-s:]}\n'
+    #     f'y_iv: {y_iv[-s:]}\n'
+    #     f'xs_iv: {xs_iv[-s:]}\n'
+    #     f'x_iv: {x_iv[-s:]}\n'
+    # )
+
+    return x_iv, y_iv, 'all'
+
+
+class Flow(msgspec.Struct):  # , frozen=True):
+    '''
+    (Financial Signal-)Flow compound type which wraps a real-time
+    shm array stream with displayed graphics (curves, charts)
+    for high level access and control as well as efficient incremental
+    update.
+
+    The intention is for this type to eventually be capable of shm-passing
+    of incrementally updated graphics stream data between actors.
+
+    '''
+    name: str
+    plot: pg.PlotItem
+    graphics: Curve
+    _shm: ShmArray
+
+    is_ohlc: bool = False
+    render: bool = True  # toggle for display loop
+
+    # downsampling state
+    _last_uppx: float = 0
+    _in_ds: bool = False
+
+    # map from uppx -> (downsampled data, incremental graphics)
+    _src_r: Optional[Renderer] = None
+    _render_table: dict[
+        Optional[int],
+        tuple[Renderer, pg.GraphicsItem],
+    ] = (None, None)
+
+    # TODO: hackery to be able to set a shm later
+    # but whilst also allowing this type to hashable,
+    # likely will require serializable token that is used to attach
+    # to the underlying shm ref after startup?
+    # _shm: Optional[ShmArray] = None  # currently, may be filled in "later"
+
+    # last read from shm (usually due to an update call)
+    _last_read: Optional[np.ndarray] = None
+
+    # cache of y-range values per x-range input.
+    _mxmns: dict[tuple[int, int], tuple[float, float]] = {}
+
+    @property
+    def shm(self) -> ShmArray:
+        return self._shm
+
+    # TODO: remove this and only allow setting through
+    # private ``._shm`` attr?
+    @shm.setter
+    def shm(self, shm: ShmArray) -> ShmArray:
+        self._shm = shm
+
+    def maxmin(
+        self,
+        lbar: int,
+        rbar: int,
+
+    ) -> tuple[float, float]:
+        '''
+        Compute the cached max and min y-range values for a given
+        x-range determined by ``lbar`` and ``rbar``.
+
+        '''
+        rkey = (lbar, rbar)
+        cached_result = self._mxmns.get(rkey)
+        if cached_result:
+            return cached_result
+
+        shm = self.shm
+        if shm is None:
+            mxmn = None
+
+        else:  # new block for profiling?..
+            arr = shm.array
+
+            # build relative indexes into shm array
+            # TODO: should we just add/use a method
+            # on the shm to do this?
+            ifirst = arr[0]['index']
+            slice_view = arr[
+                lbar - ifirst:
+                (rbar - ifirst) + 1
+            ]
+
+            if not slice_view.size:
+                mxmn = None
+
+            else:
+                if self.is_ohlc:
+                    ylow = np.min(slice_view['low'])
+                    yhigh = np.max(slice_view['high'])
+
+                else:
+                    view = slice_view[self.name]
+                    ylow = np.min(view)
+                    yhigh = np.max(view)
+
+                mxmn = ylow, yhigh
+
+            if mxmn is not None:
+                # cache new mxmn result
+                self._mxmns[rkey] = mxmn
+
+            return mxmn
+
+    def view_range(self) -> tuple[int, int]:
+        '''
+        Return the indexes in view for the associated
+        plot displaying this flow's data.
+
+        '''
+        vr = self.plot.viewRect()
+        return int(vr.left()), int(vr.right())
+
+    def datums_range(self) -> tuple[
+        int, int, int, int, int, int
+    ]:
+        '''
+        Return a range tuple for the datums present in view.
+
+        '''
+        l, r = self.view_range()
+
+        # TODO: avoid this and have shm passed
+        # in earlier.
+        if self.shm is None:
+            # haven't initialized the flow yet
+            return (0, l, 0, 0, r, 0)
+
+        array = self.shm.array
+        index = array['index']
+        start = index[0]
+        end = index[-1]
+        lbar = max(l, start)
+        rbar = min(r, end)
+        return (
+            start, l, lbar, rbar, r, end,
+        )
+
+    def read(
+        self,
+        array_field: Optional[str] = None,
+
+    ) -> tuple[
+            int, int, np.ndarray,
+            int, int, np.ndarray,
+    ]:
+        # read call
+        array = self.shm.array
+
+        indexes = array['index']
+        ifirst = indexes[0]
+        ilast = indexes[-1]
+
+        ifirst, l, lbar, rbar, r, ilast = self.datums_range()
+
+        # get read-relative indices adjusting
+        # for master shm index.
+        lbar_i = max(l, ifirst) - ifirst
+        rbar_i = min(r, ilast) - ifirst
+
+        if array_field:
+            array = array[array_field]
+
+        # TODO: we could do it this way as well no?
+        # to_draw = array[lbar - ifirst:(rbar - ifirst) + 1]
+        in_view = array[lbar_i: rbar_i + 1]
+
+        return (
+            # abs indices + full data set
+            ifirst, ilast, array,
+
+            # relative indices + in view datums
+            lbar_i, rbar_i, in_view,
+        )
+
+    def update_graphics(
+        self,
+        use_vr: bool = True,
+        render: bool = True,
+        array_key: Optional[str] = None,
+
+        profiler: Optional[pg.debug.Profiler] = None,
+        do_append: bool = True,
+
+        **kwargs,
+
+    ) -> pg.GraphicsObject:
+        '''
+        Read latest datums from shm and render to (incrementally)
+        render to graphics.
+
+        '''
+        profiler = pg.debug.Profiler(
+            msg=f'Flow.update_graphics() for {self.name}',
+            disabled=not pg_profile_enabled(),
+            ms_threshold=4,
+            # ms_threshold=ms_slower_then,
+        )
+        # shm read and slice to view
+        read = (
+            xfirst, xlast, src_array,
+            ivl, ivr, in_view,
+        ) = self.read()
+
+        profiler('read src shm data')
+
+        graphics = self.graphics
+
+        if (
+            not in_view.size
+            or not render
+        ):
+            # print('exiting early')
+            return graphics
+
+        slice_to_head: int = -1
+        should_redraw: bool = False
+        rkwargs = {}
+
+        if isinstance(graphics, BarItems):
+            # XXX: special case where we change out graphics
+            # to a line after a certain uppx threshold.
+            (
+                graphics,
+                r,
+                rkwargs,
+                should_line,
+                changed_to_line,
+            ) = render_baritems(
+                self,
+                graphics,
+                read,
+                profiler,
+                **kwargs,
+            )
+            # bars = True
+            should_redraw = changed_to_line or not should_line
+
+        else:
+            r = self._src_r
+            if not r:
+                # just using for ``.diff()`` atm..
+                r = self._src_r = Renderer(
+                    flow=self,
+                    # TODO: rename this to something with ohlc
+                    last_read=read,
+                )
+
+        # ``Curve`` derivative case(s):
+        array_key = array_key or self.name
+        # print(array_key)
+
+        # ds update config
+        new_sample_rate: bool = False
+        should_ds: bool = r._in_ds
+        showing_src_data: bool = not r._in_ds
+
+        # step_mode = getattr(graphics, '_step_mode', False)
+        step_mode = isinstance(graphics, StepCurve)
+        if step_mode:
+
+            r.allocate_xy = to_step_format
+            r.update_xy = update_step_xy
+            r.format_xy = step_to_xy
+
+            # TODO: append logic inside ``.render()`` isn't
+            # correct yet for step curves.. remove this to see it.
+            should_redraw = True
+            slice_to_head = -2
+
+        # downsampling incremental state checking
+        # check for and set std m4 downsample conditions
+        uppx = graphics.x_uppx()
+        uppx_diff = (uppx - self._last_uppx)
+        profiler(f'diffed uppx {uppx}')
+        if (
+            uppx > 1
+            and abs(uppx_diff) >= 1
+        ):
+            log.debug(
+                f'{array_key} sampler change: {self._last_uppx} -> {uppx}'
+            )
+            self._last_uppx = uppx
+
+            new_sample_rate = True
+            showing_src_data = False
+            should_ds = True
+            should_redraw = True
+
+        elif (
+            uppx <= 2
+            and self._in_ds
+        ):
+            # we should de-downsample back to our original
+            # source data so we clear our path data in prep
+            # to generate a new one from original source data.
+            new_sample_rate = True
+            showing_src_data = True
+            should_ds = False
+            should_redraw = True
+
+        # MAIN RENDER LOGIC:
+        # - determine in view data and redraw on range change
+        # - determine downsampling ops if needed
+        # - (incrementally) update ``QPainterPath``
+
+        out = r.render(
+            read,
+            array_key,
+            profiler,
+            uppx=uppx,
+            # use_vr=True,
+
+            # TODO: better way to detect and pass this?
+            # if we want to eventually cache renderers for a given uppx
+            # we should probably use this as a key + state?
+            should_redraw=should_redraw,
+            new_sample_rate=new_sample_rate,
+            should_ds=should_ds,
+            showing_src_data=showing_src_data,
+
+            slice_to_head=slice_to_head,
+            do_append=do_append,
+
+            **rkwargs,
+        )
+
+        if not out:
+            log.warning(f'{self.name} failed to render!?')
+            return graphics
+
+        path, data, reset = out
+
+        # XXX: SUPER UGGGHHH... without this we get stale cache
+        # graphics that don't update until you downsampler again..
+        if reset:
+            with graphics.reset_cache():
+                # assign output paths to graphicis obj
+                graphics.path = r.path
+                graphics.fast_path = r.fast_path
+        else:
+            # assign output paths to graphicis obj
+            graphics.path = r.path
+            graphics.fast_path = r.fast_path
+
+        graphics.draw_last_datum(
+            path,
+            src_array,
+            data,
+            reset,
+            array_key,
+        )
+
+        # TODO: is this ever better?
+        # graphics.prepareGeometryChange()
+        # profiler('.prepareGeometryChange()')
+
+        # TODO: does this actuallly help us in any way (prolly should
+        # look at the source / ask ogi). I think it avoid artifacts on
+        # wheel-scroll downsampling curve updates?
+        graphics.update()
+        profiler('.update()')
+
+        # track downsampled state
+        self._in_ds = r._in_ds
+
+        return graphics
+
+    def draw_last(
+        self,
+        array_key: Optional[str] = None,
+
+    ) -> None:
+
+        # shm read and slice to view
+        (
+            xfirst, xlast, src_array,
+            ivl, ivr, in_view,
+        ) = self.read()
+
+        g = self.graphics
+        array_key = array_key or self.name
+        x, y = g.draw_last_datum(
+            g.path,
+            src_array,
+            src_array,
+            False,  # never reset path
+            array_key,
+        )
+
+        if self._in_ds:
+            # we only care about the last pixel's
+            # worth of data since that's all the screen
+            # can represent on the last column where
+            # the most recent datum is being drawn.
+            uppx = self._last_uppx
+            y = y[-uppx:]
+            ymn, ymx = y.min(), y.max()
+            # print(f'drawing uppx={uppx} mxmn line: {ymn}, {ymx}')
+            g._last_line = QLineF(
+                x[-2], ymn,
+                x[-1], ymx,
+            )
+
+
+def by_index_and_key(
+    renderer: Renderer,
+    array: np.ndarray,
+    array_key: str,
+    vr: tuple[int, int],
+
+) -> tuple[
+    np.ndarray,
+    np.ndarray,
+    np.ndarray,
+]:
+    return array['index'], array[array_key], 'all'
+
+
+class Renderer(msgspec.Struct):
+
+    flow: Flow
+    # last array view read
+    last_read: Optional[tuple] = None
+
+    # default just returns index, and named array from data
+    format_xy: Callable[
+        [np.ndarray, str],
+        tuple[np.ndarray]
+    ] = by_index_and_key
+
+    # optional pre-graphics xy formatted data which
+    # is incrementally updated in sync with the source data.
+    allocate_xy: Optional[Callable[
+        [int, slice],
+        tuple[np.ndarray, np.nd.array]
+    ]] = None
+
+    update_xy: Optional[Callable[
+        [int, slice], None]
+    ] = None
+
+    x_data: Optional[np.ndarray] = None
+    y_data: Optional[np.ndarray] = None
+
+    # indexes which slice into the above arrays (which are allocated
+    # based on source data shm input size) and allow retrieving
+    # incrementally updated data.
+    _xy_first: int = 0
+    _xy_last: int = 0
+
+    # output graphics rendering, the main object
+    # processed in ``QGraphicsObject.paint()``
+    path: Optional[QPainterPath] = None
+    fast_path: Optional[QPainterPath] = None
+
+    # XXX: just ideas..
+    # called on the final data (transform) output to convert
+    # to "graphical data form" a format that can be passed to
+    # the ``.draw()`` implementation.
+    # graphics_t: Optional[Callable[ShmArray, np.ndarray]] = None
+    # graphics_t_shm: Optional[ShmArray] = None
+
+    # path graphics update implementation methods
+    # prepend_fn: Optional[Callable[QPainterPath, QPainterPath]] = None
+    # append_fn: Optional[Callable[QPainterPath, QPainterPath]] = None
+
+    # downsampling state
+    _last_uppx: float = 0
+    _in_ds: bool = False
+
+    # incremental update state(s)
+    _last_vr: Optional[tuple[float, float]] = None
+    _last_ivr: Optional[tuple[float, float]] = None
+
+    def diff(
+        self,
+        new_read: tuple[np.ndarray],
+
+    ) -> tuple[
+        np.ndarray,
+        np.ndarray,
+    ]:
+        (
+            last_xfirst,
+            last_xlast,
+            last_array,
+            last_ivl,
+            last_ivr,
+            last_in_view,
+        ) = self.last_read
+
+        # TODO: can the renderer just call ``Flow.read()`` directly?
+        # unpack latest source data read
+        (
+            xfirst,
+            xlast,
+            array,
+            ivl,
+            ivr,
+            in_view,
+        ) = new_read
+
+        # compute the length diffs between the first/last index entry in
+        # the input data and the last indexes we have on record from the
+        # last time we updated the curve index.
+        prepend_length = int(last_xfirst - xfirst)
+        append_length = int(xlast - last_xlast)
+
+        # blah blah blah
+        # do diffing for prepend, append and last entry
+        return (
+            slice(xfirst, last_xfirst),
+            prepend_length,
+            append_length,
+            slice(last_xlast, xlast),
+        )
+
+    def draw_path(
+        self,
+        x: np.ndarray,
+        y: np.ndarray,
+        connect: Union[str, np.ndarray] = 'all',
+        path: Optional[QPainterPath] = None,
+        redraw: bool = False,
+
+    ) -> QPainterPath:
+
+        path_was_none = path is None
+
+        if redraw and path:
+            path.clear()
+
+            # TODO: avoid this?
+            if self.fast_path:
+                self.fast_path.clear()
+
+            # profiler('cleared paths due to `should_redraw=True`')
+
+        path = pg.functions.arrayToQPath(
+            x,
+            y,
+            connect=connect,
+            finiteCheck=False,
+
+            # reserve mem allocs see:
+            # - https://doc.qt.io/qt-5/qpainterpath.html#reserve
+            # - https://doc.qt.io/qt-5/qpainterpath.html#capacity
+            # - https://doc.qt.io/qt-5/qpainterpath.html#clear
+            # XXX: right now this is based on had hoc checks on a
+            # hidpi 3840x2160 4k monitor but we should optimize for
+            # the target display(s) on the sys.
+            # if no_path_yet:
+            #     graphics.path.reserve(int(500e3))
+            # path=path,  # path re-use / reserving
+        )
+
+        # avoid mem allocs if possible
+        if path_was_none:
+            path.reserve(path.capacity())
+
+        return path
+
+    def render(
+        self,
+
+        new_read,
+        array_key: str,
+        profiler: pg.debug.Profiler,
+        uppx: float = 1,
+
+        # redraw and ds flags
+        should_redraw: bool = False,
+        new_sample_rate: bool = False,
+        should_ds: bool = False,
+        showing_src_data: bool = True,
+
+        do_append: bool = True,
+        slice_to_head: int = -1,
+        use_fpath: bool = True,
+
+        # only render datums "in view" of the ``ChartView``
+        use_vr: bool = True,
+        read_from_key: bool = True,
+
+    ) -> list[QPainterPath]:
+        '''
+        Render the current graphics path(s)
+
+        There are (at least) 3 stages from source data to graphics data:
+        - a data transform (which can be stored in additional shm)
+        - a graphics transform which converts discrete basis data to
+          a `float`-basis view-coords graphics basis. (eg. ``ohlc_flatten()``,
+          ``step_path_arrays_from_1d()``, etc.)
+
+        - blah blah blah (from notes)
+
+        '''
+        # TODO: can the renderer just call ``Flow.read()`` directly?
+        # unpack latest source data read
+        (
+            xfirst,
+            xlast,
+            array,
+            ivl,
+            ivr,
+            in_view,
+        ) = new_read
+
+        (
+            pre_slice,
+            prepend_length,
+            append_length,
+            post_slice,
+        ) = self.diff(new_read)
+
+        if self.update_xy:
+
+            shm = self.flow.shm
+
+            if self.y_data is None:
+                # we first need to allocate xy data arrays
+                # from the source data.
+                assert self.allocate_xy
+                self.x_data, self.y_data = self.allocate_xy(
+                    shm,
+                    array_key,
+                )
+                self._xy_first = shm._first.value
+                self._xy_last = shm._last.value
+                profiler('allocated xy history')
+
+            if prepend_length:
+                y_prepend = shm._array[pre_slice]
+
+                if read_from_key:
+                    y_prepend = y_prepend[array_key]
+
+                xy_data, xy_slice = self.update_xy(
+                    shm,
+                    array_key,
+
+                    # this is the pre-sliced, "normally expected"
+                    # new data that an updater would normally be
+                    # expected to process, however in some cases (like
+                    # step curves) the updater routine may want to do
+                    # the source history-data reading itself, so we pass
+                    # both here.
+                    y_prepend,
+
+                    pre_slice,
+                    prepend_length,
+                    self._xy_first,
+                    self._xy_last,
+                    is_append=False,
+                )
+                self.y_data[xy_slice] = xy_data
+                self._xy_first = shm._first.value
+                profiler('prepended xy history: {prepend_length}')
+
+            if append_length:
+                y_append = shm._array[post_slice]
+
+                if read_from_key:
+                    y_append = y_append[array_key]
+
+                xy_data, xy_slice = self.update_xy(
+                    shm,
+                    array_key,
+
+                    y_append,
+                    post_slice,
+                    append_length,
+
+                    self._xy_first,
+                    self._xy_last,
+                    is_append=True,
+                )
+                # self.y_data[post_slice] = xy_data
+                # self.y_data[xy_slice or post_slice] = xy_data
+                self.y_data[xy_slice] = xy_data
+                self._xy_last = shm._last.value
+                profiler('appened xy history: {append_length}')
+
+        if use_vr:
+            array = in_view
+        # else:
+        #     ivl, ivr = xfirst, xlast
+
+        hist = array[:slice_to_head]
+
+        # xy-path data transform: convert source data to a format
+        # able to be passed to a `QPainterPath` rendering routine.
+        if not len(hist):
+            return
+
+        x_out, y_out, connect = self.format_xy(
+            self,
+            # TODO: hist here should be the pre-sliced
+            # x/y_data in the case where allocate_xy is
+            # defined?
+            hist,
+            array_key,
+            (ivl, ivr),
+        )
+
+        profiler('sliced input arrays')
+
+        if (
+            use_vr
+        ):
+            # if a view range is passed, plan to draw the
+            # source ouput that's "in view" of the chart.
+            view_range = (ivl, ivr)
+            # print(f'{self._name} vr: {view_range}')
+
+            profiler(f'view range slice {view_range}')
+
+            vl, vr = view_range
+
+            zoom_or_append = False
+            last_vr = self._last_vr
+            last_ivr = self._last_ivr or vl, vr
+
+            # incremental in-view data update.
+            if last_vr:
+                # relative slice indices
+                lvl, lvr = last_vr
+                # abs slice indices
+                al, ar = last_ivr
+
+                # left_change = abs(x_iv[0] - al) >= 1
+                # right_change = abs(x_iv[-1] - ar) >= 1
+
+                if (
+                    # likely a zoom view change
+                    (vr - lvr) > 2 or vl < lvl
+                    # append / prepend update
+                    # we had an append update where the view range
+                    # didn't change but the data-viewed (shifted)
+                    # underneath, so we need to redraw.
+                    # or left_change and right_change and last_vr == view_range
+
+                    # not (left_change and right_change) and ivr
+                    # (
+                    # or abs(x_iv[ivr] - livr) > 1
+                ):
+                    zoom_or_append = True
+
+            self._last_vr = view_range
+            if len(x_out):
+                self._last_ivr = x_out[0], x_out[slice_to_head]
+
+        # redraw conditions
+        if (
+            prepend_length > 0
+            or new_sample_rate
+            or append_length > 0
+            or zoom_or_append
+        ):
+            should_redraw = True
+
+        path = self.path
+        fast_path = self.fast_path
+        reset = False
+
+        # redraw the entire source data if we have either of:
+        # - no prior path graphic rendered or,
+        # - we always intend to re-render the data only in view
+        if (
+            path is None
+            or should_redraw
+        ):
+            # print(f"{self.flow.name} -> REDRAWING BRUH")
+            if new_sample_rate and showing_src_data:
+                log.info(f'DEDOWN -> {array_key}')
+                self._in_ds = False
+
+            elif should_ds and uppx > 1:
+
+                x_out, y_out = xy_downsample(
+                    x_out,
+                    y_out,
+                    uppx,
+                )
+                reset = True
+                profiler(f'FULL PATH downsample redraw={should_ds}')
+                self._in_ds = True
+
+            path = self.draw_path(
+                x=x_out,
+                y=y_out,
+                connect=connect,
+                path=path,
+                redraw=True,
+            )
+
+            profiler(
+                'generated fresh path. '
+                f'(should_redraw: {should_redraw} '
+                f'should_ds: {should_ds} new_sample_rate: {new_sample_rate})'
+            )
+
+        # TODO: get this piecewise prepend working - right now it's
+        # giving heck on vwap...
+        # elif prepend_length:
+        #     breakpoint()
+
+        #     prepend_path = pg.functions.arrayToQPath(
+        #         x[0:prepend_length],
+        #         y[0:prepend_length],
+        #         connect='all'
+        #     )
+
+        #     # swap prepend path in "front"
+        #     old_path = graphics.path
+        #     graphics.path = prepend_path
+        #     # graphics.path.moveTo(new_x[0], new_y[0])
+        #     graphics.path.connectPath(old_path)
+
+        elif (
+            append_length > 0
+            and do_append
+            and not should_redraw
+        ):
+            # print(f'{array_key} append len: {append_length}')
+            new_x = x_out[-append_length - 2:]  # slice_to_head]
+            new_y = y_out[-append_length - 2:]  # slice_to_head]
+            profiler('sliced append path')
+
+            profiler(
+                f'diffed array input, append_length={append_length}'
+            )
+
+            # if should_ds:
+            #     new_x, new_y = xy_downsample(
+            #         new_x,
+            #         new_y,
+            #         uppx,
+            #     )
+            #     profiler(f'fast path downsample redraw={should_ds}')
+
+            append_path = self.draw_path(
+                x=new_x,
+                y=new_y,
+                connect=connect,
+                path=fast_path,
+            )
+            profiler('generated append qpath')
+
+            if use_fpath:
+                # an attempt at trying to make append-updates faster..
+                if fast_path is None:
+                    fast_path = append_path
+                    # fast_path.reserve(int(6e3))
+                else:
+                    fast_path.connectPath(append_path)
+                    size = fast_path.capacity()
+                    profiler(f'connected fast path w size: {size}')
+
+                    # print(f"append_path br: {append_path.boundingRect()}")
+                    # graphics.path.moveTo(new_x[0], new_y[0])
+                    # path.connectPath(append_path)
+
+                    # XXX: lol this causes a hang..
+                    # graphics.path = graphics.path.simplified()
+            else:
+                size = path.capacity()
+                profiler(f'connected history path w size: {size}')
+                path.connectPath(append_path)
+
+        self.path = path
+        self.fast_path = fast_path
+
+        # TODO: eventually maybe we can implement some kind of
+        # transform on the ``QPainterPath`` that will more or less
+        # detect the diff in "elements" terms?
+        # update diff state since we've now rendered paths.
+        self.last_read = new_read
+
+        return self.path, array, reset
diff --git a/piker/ui/_fsp.py b/piker/ui/_fsp.py
index 52763375..af03a9c6 100644
--- a/piker/ui/_fsp.py
+++ b/piker/ui/_fsp.py
@@ -75,6 +75,7 @@ def update_fsp_chart(
     flow,
     graphics_name: str,
     array_key: Optional[str],
+    **kwargs,
 
 ) -> None:
 
@@ -93,10 +94,10 @@ def update_fsp_chart(
     # update graphics
     # NOTE: this does a length check internally which allows it
     # staying above the last row check below..
-    chart.update_graphics_from_array(
+    chart.update_graphics_from_flow(
         graphics_name,
-        array,
         array_key=array_key or graphics_name,
+        **kwargs,
     )
 
     # XXX: re: ``array_key``: fsp func names must be unique meaning we
@@ -106,9 +107,6 @@ def update_fsp_chart(
     # read from last calculated value and update any label
     last_val_sticky = chart._ysticks.get(graphics_name)
     if last_val_sticky:
-        # array = shm.array[array_key]
-        # if len(array):
-        #     value = array[-1]
         last = last_row[array_key]
         last_val_sticky.update_from_data(-1, last)
 
@@ -246,20 +244,18 @@ async def run_fsp_ui(
 
             chart.draw_curve(
                 name=name,
-                data=shm.array,
+                shm=shm,
                 overlay=True,
                 color='default_light',
                 array_key=name,
                 **conf.get('chart_kwargs', {})
             )
-            # specially store ref to shm for lookup in display loop
-            chart._flows[name].shm = shm
 
         else:
             # create a new sub-chart widget for this fsp
             chart = linkedsplits.add_plot(
                 name=name,
-                array=shm.array,
+                shm=shm,
 
                 array_key=name,
                 sidepane=sidepane,
@@ -271,12 +267,6 @@ async def run_fsp_ui(
                 **conf.get('chart_kwargs', {})
             )
 
-            # XXX: ONLY for sub-chart fsps, overlays have their
-            # data looked up from the chart's internal array set.
-            # TODO: we must get a data view api going STAT!!
-            chart._shm = shm
-            chart._flows[chart.data_key].shm = shm
-
             # should **not** be the same sub-chart widget
             assert chart.name != linkedsplits.chart.name
 
@@ -445,12 +435,16 @@ class FspAdmin:
             # wait for graceful shutdown signal
             async with stream.subscribe() as stream:
                 async for msg in stream:
-                    if msg == 'update':
+                    info = msg.get('fsp_update')
+                    if info:
                         # if the chart isn't hidden try to update
                         # the data on screen.
                         if not self.linked.isHidden():
                             log.info(f'Re-syncing graphics for fsp: {ns_path}')
-                            self.linked.graphics_cycle(trigger_all=True)
+                            self.linked.graphics_cycle(
+                                trigger_all=True,
+                                prepend_update_index=info['first'],
+                            )
                     else:
                         log.info(f'recved unexpected fsp engine msg: {msg}')
 
@@ -626,7 +620,7 @@ async def open_vlm_displays(
         shm = ohlcv
         chart = linked.add_plot(
             name='volume',
-            array=shm.array,
+            shm=shm,
 
             array_key='volume',
             sidepane=sidepane,
@@ -639,10 +633,9 @@ async def open_vlm_displays(
             # the curve item internals are pretty convoluted.
             style='step',
         )
-        chart._flows['volume'].shm = ohlcv
 
         # force 0 to always be in view
-        def maxmin(
+        def multi_maxmin(
             names: list[str],
 
         ) -> tuple[float, float]:
@@ -658,7 +651,7 @@ async def open_vlm_displays(
 
             return 0, mx
 
-        chart.view.maxmin = partial(maxmin, names=['volume'])
+        chart.view.maxmin = partial(multi_maxmin, names=['volume'])
 
         # TODO: fix the x-axis label issue where if you put
         # the axis on the left it's totally not lined up...
@@ -666,11 +659,6 @@ async def open_vlm_displays(
         # chart.hideAxis('right')
         # chart.showAxis('left')
 
-        # XXX: ONLY for sub-chart fsps, overlays have their
-        # data looked up from the chart's internal array set.
-        # TODO: we must get a data view api going STAT!!
-        chart._shm = shm
-
         # send back new chart to caller
         task_status.started(chart)
 
@@ -685,9 +673,9 @@ async def open_vlm_displays(
 
         last_val_sticky.update_from_data(-1, value)
 
-        vlm_curve = chart.update_graphics_from_array(
+        vlm_curve = chart.update_graphics_from_flow(
             'volume',
-            shm.array,
+            # shm.array,
         )
 
         # size view to data once at outset
@@ -753,19 +741,20 @@ async def open_vlm_displays(
                'dolla_vlm',
                'dark_vlm',
             ]
-            dvlm_rate_fields = [
-                'dvlm_rate',
-                'dark_dvlm_rate',
-            ]
+            # dvlm_rate_fields = [
+            #     'dvlm_rate',
+            #     'dark_dvlm_rate',
+            # ]
             trade_rate_fields = [
                 'trade_rate',
                 'dark_trade_rate',
             ]
 
             group_mxmn = partial(
-                maxmin,
+                multi_maxmin,
                 # keep both regular and dark vlm in view
-                names=fields + dvlm_rate_fields,
+                names=fields,
+                # names=fields + dvlm_rate_fields,
             )
 
             # add custom auto range handler
@@ -795,9 +784,8 @@ async def open_vlm_displays(
                         color = 'bracket'
 
                     curve, _ = chart.draw_curve(
-                        # name='dolla_vlm',
                         name=name,
-                        data=shm.array,
+                        shm=shm,
                         array_key=name,
                         overlay=pi,
                         color=color,
@@ -812,7 +800,6 @@ async def open_vlm_displays(
                     # ``.draw_curve()``.
                     flow = chart._flows[name]
                     assert flow.plot is pi
-                    flow.shm = shm
 
             chart_curves(
                 fields,
@@ -834,11 +821,11 @@ async def open_vlm_displays(
             )
             await started.wait()
 
-            chart_curves(
-                dvlm_rate_fields,
-                dvlm_pi,
-                fr_shm,
-            )
+            # chart_curves(
+            #     dvlm_rate_fields,
+            #     dvlm_pi,
+            #     fr_shm,
+            # )
 
             # TODO: is there a way to "sync" the dual axes such that only
             # one curve is needed?
@@ -847,7 +834,9 @@ async def open_vlm_displays(
             # liquidity events (well at least on low OHLC periods - 1s).
             vlm_curve.hide()
             chart.removeItem(vlm_curve)
-            chart._flows.pop('volume')
+            vflow = chart._flows['volume']
+            vflow.render = False
+
             # avoid range sorting on volume once disabled
             chart.view.disable_auto_yrange()
 
@@ -874,7 +863,7 @@ async def open_vlm_displays(
             )
             # add custom auto range handler
             tr_pi.vb.maxmin = partial(
-                maxmin,
+                multi_maxmin,
                 # keep both regular and dark vlm in view
                 names=trade_rate_fields,
             )
@@ -902,10 +891,10 @@ async def open_vlm_displays(
 
         # built-in vlm fsps
         for target, conf in {
-            tina_vwap: {
-                'overlay': 'ohlc',  # overlays with OHLCV (main) chart
-                'anchor': 'session',
-            },
+            # tina_vwap: {
+            #     'overlay': 'ohlc',  # overlays with OHLCV (main) chart
+            #     'anchor': 'session',
+            # },
         }.items():
             started = await admin.open_fsp_chart(
                 target,
diff --git a/piker/ui/_interaction.py b/piker/ui/_interaction.py
index 4872f595..a659612a 100644
--- a/piker/ui/_interaction.py
+++ b/piker/ui/_interaction.py
@@ -20,7 +20,6 @@ Chart view box primitives
 """
 from __future__ import annotations
 from contextlib import asynccontextmanager
-# import itertools
 import time
 from typing import Optional, Callable
 
@@ -35,10 +34,9 @@ import trio
 
 from ..log import get_logger
 from .._profile import pg_profile_enabled, ms_slower_then
-from ._style import _min_points_to_show
+# from ._style import _min_points_to_show
 from ._editors import SelectRect
 from . import _event
-from ._ohlc import BarItems
 
 
 log = get_logger(__name__)
@@ -486,15 +484,18 @@ class ChartView(ViewBox):
 
         # don't zoom more then the min points setting
         l, lbar, rbar, r = chart.bars_range()
-        vl = r - l
+        # vl = r - l
 
-        if ev.delta() > 0 and vl <= _min_points_to_show:
-            log.debug("Max zoom bruh...")
-            return
+        # if ev.delta() > 0 and vl <= _min_points_to_show:
+        #     log.debug("Max zoom bruh...")
+        #     return
 
-        if ev.delta() < 0 and vl >= len(chart._arrays[chart.name]) + 666:
-            log.debug("Min zoom bruh...")
-            return
+        # if (
+        #     ev.delta() < 0
+        #     and vl >= len(chart._flows[chart.name].shm.array) + 666
+        # ):
+        #     log.debug("Min zoom bruh...")
+        #     return
 
         # actual scaling factor
         s = 1.015 ** (ev.delta() * -1 / 20)  # self.state['wheelScaleFactor'])
@@ -568,11 +569,23 @@ class ChartView(ViewBox):
 
             self._resetTarget()
             self.scaleBy(s, focal)
+
+            # XXX: the order of the next 2 lines i'm pretty sure
+            # matters, we want the resize to trigger before the graphics
+            # update, but i gotta feelin that because this one is signal
+            # based (and thus not necessarily sync invoked right away)
+            # that calling the resize method manually might work better.
             self.sigRangeChangedManually.emit(mask)
 
-            # self._ic.set()
-            # self._ic = None
-            # self.chart.resume_all_feeds()
+            # XXX: without this is seems as though sometimes
+            # when zooming in from far out (and maybe vice versa?)
+            # the signal isn't being fired enough since if you pan
+            # just after you'll see further downsampling code run
+            # (pretty noticeable on the OHLC ds curve) but with this
+            # that never seems to happen? Only question is how much this
+            # "double work" is causing latency when these missing event
+            # fires don't happen?
+            self.maybe_downsample_graphics()
 
             ev.accept()
 
@@ -734,9 +747,8 @@ class ChartView(ViewBox):
 
         # flag to prevent triggering sibling charts from the same linked
         # set from recursion errors.
-        autoscale_linked_plots: bool = True,
+        autoscale_linked_plots: bool = False,
         name: Optional[str] = None,
-        # autoscale_overlays: bool = False,
 
     ) -> None:
         '''
@@ -747,9 +759,12 @@ class ChartView(ViewBox):
         data set.
 
         '''
+        name = self.name
+        # print(f'YRANGE ON {name}')
         profiler = pg.debug.Profiler(
+            msg=f'`ChartView._set_yrange()`: `{name}`',
             disabled=not pg_profile_enabled(),
-            gt=ms_slower_then,
+            ms_threshold=ms_slower_then,
             delayed=True,
         )
         set_range = True
@@ -775,45 +790,22 @@ class ChartView(ViewBox):
         elif yrange is not None:
             ylow, yhigh = yrange
 
-        # calculate max, min y values in viewable x-range from data.
-        # Make sure min bars/datums on screen is adhered.
-        else:
-            br = bars_range or chart.bars_range()
-            profiler(f'got bars range: {br}')
-
-            # TODO: maybe should be a method on the
-            # chart widget/item?
-            # if False:
-            # if autoscale_linked_plots:
-            #     # avoid recursion by sibling plots
-            #     linked = self.linkedsplits
-            #     plots = list(linked.subplots.copy().values())
-            #     main = linked.chart
-            #     if main:
-            #         plots.append(main)
-
-            #     for chart in plots:
-            #         if chart and not chart._static_yrange:
-            #             chart.cv._set_yrange(
-            #                 bars_range=br,
-            #                 autoscale_linked_plots=False,
-            #             )
-            #     profiler('autoscaled linked plots')
-
         if set_range:
 
+            # XXX: only compute the mxmn range
+            # if none is provided as input!
             if not yrange:
-                # XXX: only compute the mxmn range
-                # if none is provided as input!
+                # flow = chart._flows[name]
                 yrange = self._maxmin()
 
                 if yrange is None:
-                    log.warning(f'No yrange provided for {self.name}!?')
+                    log.warning(f'No yrange provided for {name}!?')
+                    print(f"WTF NO YRANGE {name}")
                     return
 
             ylow, yhigh = yrange
 
-            profiler(f'maxmin(): {yrange}')
+            profiler(f'callback ._maxmin(): {yrange}')
 
             # view margins: stay within a % of the "true range"
             diff = yhigh - ylow
@@ -830,6 +822,8 @@ class ChartView(ViewBox):
             self.setYRange(ylow, yhigh)
             profiler(f'set limits: {(ylow, yhigh)}')
 
+        profiler.finish()
+
     def enable_auto_yrange(
         self,
         src_vb: Optional[ChartView] = None,
@@ -843,17 +837,9 @@ class ChartView(ViewBox):
         if src_vb is None:
             src_vb = self
 
-        # such that when a linked chart changes its range
-        # this local view is also automatically changed and
-        # resized to data.
-        src_vb.sigXRangeChanged.connect(self._set_yrange)
-
         # splitter(s) resizing
         src_vb.sigResized.connect(self._set_yrange)
 
-        # mouse wheel doesn't emit XRangeChanged
-        src_vb.sigRangeChangedManually.connect(self._set_yrange)
-
         # TODO: a smarter way to avoid calling this needlessly?
         # 2 things i can think of:
         # - register downsample-able graphics specially and only
@@ -864,15 +850,16 @@ class ChartView(ViewBox):
             self.maybe_downsample_graphics
         )
 
-    def disable_auto_yrange(
-        self,
-    ) -> None:
+        # mouse wheel doesn't emit XRangeChanged
+        src_vb.sigRangeChangedManually.connect(self._set_yrange)
 
-        # self._chart._static_yrange = 'axis'
+        # src_vb.sigXRangeChanged.connect(self._set_yrange)
+        # src_vb.sigXRangeChanged.connect(
+        #     self.maybe_downsample_graphics
+        # )
+
+    def disable_auto_yrange(self) -> None:
 
-        self.sigXRangeChanged.disconnect(
-            self._set_yrange,
-        )
         self.sigResized.disconnect(
             self._set_yrange,
         )
@@ -883,6 +870,11 @@ class ChartView(ViewBox):
             self._set_yrange,
         )
 
+        # self.sigXRangeChanged.disconnect(self._set_yrange)
+        # self.sigXRangeChanged.disconnect(
+        #     self.maybe_downsample_graphics
+        # )
+
     def x_uppx(self) -> float:
         '''
         Return the "number of x units" within a single
@@ -890,7 +882,7 @@ class ChartView(ViewBox):
         graphics items which are our children.
 
         '''
-        graphics = list(self._chart._graphics.values())
+        graphics = [f.graphics for f in self._chart._flows.values()]
         if not graphics:
             return 0
 
@@ -901,25 +893,21 @@ class ChartView(ViewBox):
         else:
             return 0
 
-    def maybe_downsample_graphics(self):
-
-        uppx = self.x_uppx()
-        if (
-            # we probably want to drop this once we are "drawing in
-            # view" for downsampled flows..
-            uppx and uppx > 16
-            and self._ic is not None
-        ):
-            # don't bother updating since we're zoomed out bigly and
-            # in a pan-interaction, in which case we shouldn't be
-            # doing view-range based rendering (at least not yet).
-            # print(f'{uppx} exiting early!')
-            return
+    def maybe_downsample_graphics(
+        self,
+        autoscale_overlays: bool = True,
+    ):
 
         profiler = pg.debug.Profiler(
+            msg=f'ChartView.maybe_downsample_graphics() for {self.name}',
             disabled=not pg_profile_enabled(),
-            gt=3,
-            delayed=True,
+
+            # XXX: important to avoid not seeing underlying
+            # ``.update_graphics_from_flow()`` nested profiling likely
+            # due to the way delaying works and garbage collection of
+            # the profiler in the delegated method calls.
+            ms_threshold=6,
+            # ms_threshold=ms_slower_then,
         )
 
         # TODO: a faster single-loop-iterator way of doing this XD
@@ -928,19 +916,32 @@ class ChartView(ViewBox):
         plots = linked.subplots | {chart.name: chart}
         for chart_name, chart in plots.items():
             for name, flow in chart._flows.items():
-                graphics = flow.graphics
 
-                use_vr = False
-                if isinstance(graphics, BarItems):
-                    use_vr = True
+                if (
+                    not flow.render
+
+                    # XXX: super important to be aware of this.
+                    # or not flow.graphics.isVisible()
+                ):
+                    continue
 
                 # pass in no array which will read and render from the last
                 # passed array (normally provided by the display loop.)
-                chart.update_graphics_from_array(
+                chart.update_graphics_from_flow(
                     name,
-                    use_vr=use_vr,
-                    profiler=profiler,
+                    use_vr=True,
                 )
-                profiler(f'range change updated {chart_name}:{name}')
 
-        profiler.finish()
+                # for each overlay on this chart auto-scale the
+                # y-range to max-min values.
+                if autoscale_overlays:
+                    overlay = chart.pi_overlay
+                    if overlay:
+                        for pi in overlay.overlays:
+                            pi.vb._set_yrange(
+                                # TODO: get the range once up front...
+                                # bars_range=br,
+                            )
+                    profiler('autoscaled linked plots')
+
+                profiler(f'<{chart_name}>.update_graphics_from_flow({name})')
diff --git a/piker/ui/_ohlc.py b/piker/ui/_ohlc.py
index 44dbb0c2..dbe4c18e 100644
--- a/piker/ui/_ohlc.py
+++ b/piker/ui/_ohlc.py
@@ -25,17 +25,13 @@ from typing import (
 
 import numpy as np
 import pyqtgraph as pg
-from numba import njit, float64, int64  # , optional
 from PyQt5 import QtCore, QtGui, QtWidgets
 from PyQt5.QtCore import QLineF, QPointF
-# from numba import types as ntypes
-# from ..data._source import numba_ohlc_dtype
+from PyQt5.QtGui import QPainterPath
 
 from .._profile import pg_profile_enabled, ms_slower_then
 from ._style import hcolor
 from ..log import get_logger
-from ._curve import FastAppendCurve
-from ._compression import ohlc_flatten
 
 if TYPE_CHECKING:
     from ._chart import LinkedSplits
@@ -46,7 +42,8 @@ log = get_logger(__name__)
 
 def bar_from_ohlc_row(
     row: np.ndarray,
-    w: float
+    # 0.5 is no overlap between arms, 1.0 is full overlap
+    w: float = 0.43
 
 ) -> tuple[QLineF]:
     '''
@@ -84,128 +81,11 @@ def bar_from_ohlc_row(
     return [hl, o, c]
 
 
-@njit(
-    # TODO: for now need to construct this manually for readonly arrays, see
-    # https://github.com/numba/numba/issues/4511
-    # ntypes.tuple((float64[:], float64[:], float64[:]))(
-    #     numba_ohlc_dtype[::1],  # contiguous
-    #     int64,
-    #     optional(float64),
-    # ),
-    nogil=True
-)
-def path_arrays_from_ohlc(
-    data: np.ndarray,
-    start: int64,
-    bar_gap: float64 = 0.43,
-
-) -> np.ndarray:
-    '''
-    Generate an array of lines objects from input ohlc data.
-
-    '''
-    size = int(data.shape[0] * 6)
-
-    x = np.zeros(
-        # data,
-        shape=size,
-        dtype=float64,
-    )
-    y, c = x.copy(), x.copy()
-
-    # TODO: report bug for assert @
-    # /home/goodboy/repos/piker/env/lib/python3.8/site-packages/numba/core/typing/builtins.py:991
-    for i, q in enumerate(data[start:], start):
-
-        # TODO: ask numba why this doesn't work..
-        # open, high, low, close, index = q[
-        #     ['open', 'high', 'low', 'close', 'index']]
-
-        open = q['open']
-        high = q['high']
-        low = q['low']
-        close = q['close']
-        index = float64(q['index'])
-
-        istart = i * 6
-        istop = istart + 6
-
-        # x,y detail the 6 points which connect all vertexes of a ohlc bar
-        x[istart:istop] = (
-            index - bar_gap,
-            index,
-            index,
-            index,
-            index,
-            index + bar_gap,
-        )
-        y[istart:istop] = (
-            open,
-            open,
-            low,
-            high,
-            close,
-            close,
-        )
-
-        # specifies that the first edge is never connected to the
-        # prior bars last edge thus providing a small "gap"/"space"
-        # between bars determined by ``bar_gap``.
-        c[istart:istop] = (1, 1, 1, 1, 1, 0)
-
-    return x, y, c
-
-
-def gen_qpath(
-    data: np.ndarray,
-    start: int,  # XXX: do we need this?
-    w: float,
-    path: Optional[QtGui.QPainterPath] = None,
-
-) -> QtGui.QPainterPath:
-
-    path_was_none = path is None
-
-    profiler = pg.debug.Profiler(
-        msg='gen_qpath ohlc',
-        disabled=not pg_profile_enabled(),
-        gt=ms_slower_then,
-    )
-
-    x, y, c = path_arrays_from_ohlc(
-        data,
-        start,
-        bar_gap=w,
-    )
-    profiler("generate stream with numba")
-
-    # TODO: numba the internals of this!
-    path = pg.functions.arrayToQPath(
-        x,
-        y,
-        connect=c,
-        path=path,
-    )
-
-    # avoid mem allocs if possible
-    if path_was_none:
-        path.reserve(path.capacity())
-
-    profiler("generate path with arrayToQPath")
-
-    return path
-
-
 class BarItems(pg.GraphicsObject):
     '''
     "Price range" bars graphics rendered from a OHLC sampled sequence.
 
     '''
-    sigPlotChanged = QtCore.pyqtSignal(object)
-
-    # 0.5 is no overlap between arms, 1.0 is full overlap
-    w: float = 0.43
-
     def __init__(
         self,
         linked: LinkedSplits,
@@ -225,388 +105,13 @@ class BarItems(pg.GraphicsObject):
         self.last_bar_pen = pg.mkPen(hcolor(last_bar_color), width=2)
         self._name = name
 
-        self._ds_line_xy: Optional[
-            tuple[np.ndarray, np.ndarray]
-        ] = None
-
-        # NOTE: this prevents redraws on mouse interaction which is
-        # a huge boon for avg interaction latency.
-
-        # TODO: one question still remaining is if this makes trasform
-        # interactions slower (such as zooming) and if so maybe if/when
-        # we implement a "history" mode for the view we disable this in
-        # that mode?
         self.setCacheMode(QtWidgets.QGraphicsItem.DeviceCoordinateCache)
-
-        self._pi = plotitem
-        self.path = QtGui.QPainterPath()
-        self.fast_path = QtGui.QPainterPath()
-
-        self._xrange: tuple[int, int]
-        self._yrange: tuple[float, float]
-        self._vrange = None
-
-        # TODO: don't render the full backing array each time
-        # self._path_data = None
+        self.path = QPainterPath()
         self._last_bar_lines: Optional[tuple[QLineF, ...]] = None
 
-        # track the current length of drawable lines within the larger array
-        self.start_index: int = 0
-        self.stop_index: int = 0
-
-        # downsampler-line state
-        self._in_ds: bool = False
-        self._ds_line: Optional[FastAppendCurve] = None
-        self._dsi: tuple[int, int] = 0, 0
-        self._xs_in_px: float = 0
-
-    def draw_from_data(
-        self,
-        ohlc: np.ndarray,
-        start: int = 0,
-
-    ) -> QtGui.QPainterPath:
-        '''
-        Draw OHLC datum graphics from a ``np.ndarray``.
-
-        This routine is usually only called to draw the initial history.
-
-        '''
-        hist, last = ohlc[:-1], ohlc[-1]
-        self.path = gen_qpath(hist, start, self.w)
-
-        # save graphics for later reference and keep track
-        # of current internal "last index"
-        # self.start_index = len(ohlc)
-        index = ohlc['index']
-        self._xrange = (index[0], index[-1])
-        self._yrange = (
-            np.nanmax(ohlc['high']),
-            np.nanmin(ohlc['low']),
-        )
-
-        # up to last to avoid double draw of last bar
-        self._last_bar_lines = bar_from_ohlc_row(last, self.w)
-
-        x, y = self._ds_line_xy = ohlc_flatten(ohlc)
-
-        # TODO: figuring out the most optimial size for the ideal
-        # curve-path by,
-        # - calcing the display's max px width `.screen()`
-        # - drawing a curve and figuring out it's capacity:
-        #   https://doc.qt.io/qt-5/qpainterpath.html#capacity
-        # - reserving that cap for each curve-mapped-to-shm with
-
-        # - leveraging clearing when needed to redraw the entire
-        #   curve that does not release mem allocs:
-        #   https://doc.qt.io/qt-5/qpainterpath.html#clear
-        curve = FastAppendCurve(
-            y=y,
-            x=x,
-            name='OHLC',
-            color=self._color,
-        )
-        curve.hide()
-        self._pi.addItem(curve)
-        self._ds_line = curve
-
-        self._ds_xrange = (index[0], index[-1])
-
-        # trigger render
-        # https://doc.qt.io/qt-5/qgraphicsitem.html#update
-        self.update()
-
-        return self.path
-
     def x_uppx(self) -> int:
-        if self._ds_line:
-            return self._ds_line.x_uppx()
-        else:
-            return 0
-
-    def update_from_array(
-        self,
-
-        # full array input history
-        ohlc: np.ndarray,
-
-        # pre-sliced array data that's "in view"
-        ohlc_iv: np.ndarray,
-
-        view_range: Optional[tuple[int, int]] = None,
-        profiler: Optional[pg.debug.Profiler] = None,
-
-    ) -> None:
-        '''
-        Update the last datum's bar graphic from input data array.
-
-        This routine should be interface compatible with
-        ``pg.PlotCurveItem.setData()``. Normally this method in
-        ``pyqtgraph`` seems to update all the data passed to the
-        graphics object, and then update/rerender, but here we're
-        assuming the prior graphics havent changed (OHLC history rarely
-        does) so this "should" be simpler and faster.
-
-        This routine should be made (transitively) as fast as possible.
-
-        '''
-        profiler = profiler or pg.debug.Profiler(
-            disabled=not pg_profile_enabled(),
-            gt=ms_slower_then,
-            delayed=True,
-        )
-
-        # index = self.start_index
-        istart, istop = self._xrange
-        ds_istart, ds_istop = self._ds_xrange
-
-        index = ohlc['index']
-        first_index, last_index = index[0], index[-1]
-
-        # length = len(ohlc)
-        # prepend_length = istart - first_index
-        # append_length = last_index - istop
-
-        # ds_prepend_length = ds_istart - first_index
-        # ds_append_length = last_index - ds_istop
-
-        flip_cache = False
-
-        x_gt = 16
-        if self._ds_line:
-            uppx = self._ds_line.x_uppx()
-        else:
-            uppx = 0
-
-        should_line = self._in_ds
-        if (
-            self._in_ds
-            and uppx < x_gt
-        ):
-            should_line = False
-
-        elif (
-            not self._in_ds
-            and uppx >= x_gt
-        ):
-            should_line = True
-
-        profiler('ds logic complete')
-
-        if should_line:
-            # update the line graphic
-            # x, y = self._ds_line_xy = ohlc_flatten(ohlc_iv)
-            x, y = self._ds_line_xy = ohlc_flatten(ohlc)
-            x_iv, y_iv = self._ds_line_xy = ohlc_flatten(ohlc_iv)
-            profiler('flattening bars to line')
-
-            # TODO: we should be diffing the amount of new data which
-            # needs to be downsampled. Ideally we actually are just
-            # doing all the ds-ing in sibling actors so that the data
-            # can just be read and rendered to graphics on events of our
-            # choice.
-            # diff = do_diff(ohlc, new_bit)
-            curve = self._ds_line
-            curve.update_from_array(
-                x=x,
-                y=y,
-                x_iv=x_iv,
-                y_iv=y_iv,
-                view_range=None,  # hack
-                profiler=profiler,
-            )
-            profiler('updated ds line')
-
-            if not self._in_ds:
-                # hide bars and show line
-                self.hide()
-                # XXX: is this actually any faster?
-                # self._pi.removeItem(self)
-
-                # TODO: a `.ui()` log level?
-                log.info(
-                    f'downsampling to line graphic {self._name}'
-                )
-
-                # self._pi.addItem(curve)
-                curve.show()
-                curve.update()
-                self._in_ds = True
-
-            # stop here since we don't need to update bars path any more
-            # as we delegate to the downsample line with updates.
-            profiler.finish()
-            # print('terminating early')
-            return
-
-        else:
-            # we should be in bars mode
-
-            if self._in_ds:
-                # flip back to bars graphics and hide the downsample line.
-                log.info(f'showing bars graphic {self._name}')
-
-                curve = self._ds_line
-                curve.hide()
-                # self._pi.removeItem(curve)
-
-                # XXX: is this actually any faster?
-                # self._pi.addItem(self)
-                self.show()
-                self._in_ds = False
-
-            # generate in_view path
-            self.path = gen_qpath(
-                ohlc_iv,
-                0,
-                self.w,
-                # path=self.path,
-            )
-
-            # TODO: to make the downsampling faster
-            # - allow mapping only a range of lines thus only drawing as
-            #   many bars as exactly specified.
-            # - move ohlc "flattening" to a shmarr
-            # - maybe move all this embedded logic to a higher
-            #   level type?
-
-            # if prepend_length:
-            #     # new history was added and we need to render a new path
-            #     prepend_bars = ohlc[:prepend_length]
-
-            # if ds_prepend_length:
-            #     ds_prepend_bars = ohlc[:ds_prepend_length]
-            #     pre_x, pre_y = ohlc_flatten(ds_prepend_bars)
-            #     fx = np.concatenate((pre_x, fx))
-            #     fy = np.concatenate((pre_y, fy))
-            #     profiler('ds line prepend diff complete')
-
-            # if append_length:
-            #     # generate new graphics to match provided array
-            #     # path appending logic:
-            #     # we need to get the previous "current bar(s)" for the time step
-            #     # and convert it to a sub-path to append to the historical set
-            #     # new_bars = ohlc[istop - 1:istop + append_length - 1]
-            #     append_bars = ohlc[-append_length - 1:-1]
-            #     # print(f'ohlc bars to append size: {append_bars.size}\n')
-
-            # if ds_append_length:
-            #     ds_append_bars = ohlc[-ds_append_length - 1:-1]
-            #     post_x, post_y = ohlc_flatten(ds_append_bars)
-            #     print(
-            #         f'ds curve to append sizes: {(post_x.size, post_y.size)}'
-            #     )
-            #     fx = np.concatenate((fx, post_x))
-            #     fy = np.concatenate((fy, post_y))
-
-            #     profiler('ds line append diff complete')
-
-            profiler('array diffs complete')
-
-            # does this work?
-            last = ohlc[-1]
-            # fy[-1] = last['close']
-
-            # # incremental update and cache line datums
-            # self._ds_line_xy = fx, fy
-
-            # maybe downsample to line
-            # ds = self.maybe_downsample()
-            # if ds:
-            #     # if we downsample to a line don't bother with
-            #     # any more path generation / updates
-            #     self._ds_xrange = first_index, last_index
-            #     profiler('downsampled to line')
-            #     return
-
-            # print(in_view.size)
-
-            # if self.path:
-            #     self.path = path
-            #     self.path.reserve(path.capacity())
-            #     self.path.swap(path)
-
-            # path updates
-            # if prepend_length:
-            #     # XXX: SOMETHING IS MAYBE FISHY HERE what with the old_path
-            #     # y value not matching the first value from
-            #     # ohlc[prepend_length + 1] ???
-            #     prepend_path = gen_qpath(prepend_bars, 0, self.w)
-            #     old_path = self.path
-            #     self.path = prepend_path
-            #     self.path.addPath(old_path)
-            #     profiler('path PREPEND')
-
-            # if append_length:
-            #     append_path = gen_qpath(append_bars, 0, self.w)
-
-            #     self.path.moveTo(
-            #         float(istop - self.w),
-            #         float(append_bars[0]['open'])
-            #     )
-            #     self.path.addPath(append_path)
-
-            #     profiler('path APPEND')
-            #     fp = self.fast_path
-            #     if fp is None:
-            #         self.fast_path = append_path
-
-            #     else:
-            #         fp.moveTo(
-            #             float(istop - self.w), float(new_bars[0]['open'])
-            #         )
-            #         fp.addPath(append_path)
-
-            #     self.setCacheMode(QtWidgets.QGraphicsItem.NoCache)
-            #     flip_cache = True
-
-            self._xrange = first_index, last_index
-
-            # trigger redraw despite caching
-            self.prepareGeometryChange()
-
-            # generate new lines objects for updatable "current bar"
-            self._last_bar_lines = bar_from_ohlc_row(last, self.w)
-
-            # last bar update
-            i, o, h, l, last, v = last[
-                ['index', 'open', 'high', 'low', 'close', 'volume']
-            ]
-            # assert i == self.start_index - 1
-            # assert i == last_index
-            body, larm, rarm = self._last_bar_lines
-
-            # XXX: is there a faster way to modify this?
-            rarm.setLine(rarm.x1(), last, rarm.x2(), last)
-
-            # writer is responsible for changing open on "first" volume of bar
-            larm.setLine(larm.x1(), o, larm.x2(), o)
-
-            if l != h:  # noqa
-
-                if body is None:
-                    body = self._last_bar_lines[0] = QLineF(i, l, i, h)
-                else:
-                    # update body
-                    body.setLine(i, l, i, h)
-
-                # XXX: pretty sure this is causing an issue where the bar has
-                # a large upward move right before the next sample and the body
-                # is getting set to None since the next bar is flat but the shm
-                # array index update wasn't read by the time this code runs. Iow
-                # we're doing this removal of the body for a bar index that is
-                # now out of date / from some previous sample. It's weird
-                # though because i've seen it do this to bars i - 3 back?
-
-            profiler('last bar set')
-
-            self.update()
-            profiler('.update()')
-
-            if flip_cache:
-                self.setCacheMode(QtWidgets.QGraphicsItem.DeviceCoordinateCache)
-
-            profiler.finish()
+        # we expect the downsample curve report this.
+        return 0
 
     def boundingRect(self):
         # Qt docs: https://doc.qt.io/qt-5/qgraphicsitem.html#boundingRect
@@ -630,16 +135,6 @@ class BarItems(pg.GraphicsObject):
             hb.bottomRight(),
         )
 
-        # fp = self.fast_path
-        # if fp:
-        #     fhb = fp.controlPointRect()
-        #     print((hb_tl, hb_br))
-        #     print(fhb)
-        #     hb_tl, hb_br = (
-        #         fhb.topLeft() + hb.topLeft(),
-        #         fhb.bottomRight() + hb.bottomRight(),
-        #     )
-
         # need to include last bar height or BR will be off
         mx_y = hb_br.y()
         mn_y = hb_tl.y()
@@ -675,12 +170,9 @@ class BarItems(pg.GraphicsObject):
 
     ) -> None:
 
-        if self._in_ds:
-            return
-
         profiler = pg.debug.Profiler(
             disabled=not pg_profile_enabled(),
-            gt=ms_slower_then,
+            ms_threshold=ms_slower_then,
         )
 
         # p.setCompositionMode(0)
@@ -692,13 +184,67 @@ class BarItems(pg.GraphicsObject):
         # lead to any perf gains other then when zoomed in to less bars
         # in view.
         p.setPen(self.last_bar_pen)
-        p.drawLines(*tuple(filter(bool, self._last_bar_lines)))
-        profiler('draw last bar')
+        if self._last_bar_lines:
+            p.drawLines(*tuple(filter(bool, self._last_bar_lines)))
+            profiler('draw last bar')
 
         p.setPen(self.bars_pen)
         p.drawPath(self.path)
         profiler(f'draw history path: {self.path.capacity()}')
 
-        # if self.fast_path:
-        #     p.drawPath(self.fast_path)
-        #     profiler('draw fast path')
+    def draw_last_datum(
+        self,
+        path: QPainterPath,
+        src_data: np.ndarray,
+        render_data: np.ndarray,
+        reset: bool,
+        array_key: str,
+
+        fields: list[str] = [
+            'index',
+            'open',
+            'high',
+            'low',
+            'close',
+        ],
+
+    ) -> None:
+
+        # relevant fields
+        ohlc = src_data[fields]
+        last_row = ohlc[-1:]
+
+        # individual values
+        last_row = i, o, h, l, last = ohlc[-1]
+
+        # generate new lines objects for updatable "current bar"
+        self._last_bar_lines = bar_from_ohlc_row(last_row)
+
+        # assert i == graphics.start_index - 1
+        # assert i == last_index
+        body, larm, rarm = self._last_bar_lines
+
+        # XXX: is there a faster way to modify this?
+        rarm.setLine(rarm.x1(), last, rarm.x2(), last)
+
+        # writer is responsible for changing open on "first" volume of bar
+        larm.setLine(larm.x1(), o, larm.x2(), o)
+
+        if l != h:  # noqa
+
+            if body is None:
+                body = self._last_bar_lines[0] = QLineF(i, l, i, h)
+            else:
+                # update body
+                body.setLine(i, l, i, h)
+
+            # XXX: pretty sure this is causing an issue where the
+            # bar has a large upward move right before the next
+            # sample and the body is getting set to None since the
+            # next bar is flat but the shm array index update wasn't
+            # read by the time this code runs. Iow we're doing this
+            # removal of the body for a bar index that is now out of
+            # date / from some previous sample. It's weird though
+            # because i've seen it do this to bars i - 3 back?
+
+        return ohlc['index'], ohlc['close']
diff --git a/piker/ui/_pathops.py b/piker/ui/_pathops.py
new file mode 100644
index 00000000..83b46f43
--- /dev/null
+++ b/piker/ui/_pathops.py
@@ -0,0 +1,236 @@
+# piker: trading gear for hackers
+# Copyright (C) 2018-present  Tyler Goodlet (in stewardship of piker0)
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+"""
+Super fast ``QPainterPath`` generation related operator routines.
+
+"""
+from __future__ import annotations
+from typing import (
+    # Optional,
+    TYPE_CHECKING,
+)
+
+import numpy as np
+from numpy.lib import recfunctions as rfn
+from numba import njit, float64, int64  # , optional
+# import pyqtgraph as pg
+from PyQt5 import QtGui
+# from PyQt5.QtCore import QLineF, QPointF
+
+from ..data._sharedmem import (
+    ShmArray,
+)
+# from .._profile import pg_profile_enabled, ms_slower_then
+from ._compression import (
+    ds_m4,
+)
+
+if TYPE_CHECKING:
+    from ._flows import Renderer
+
+
+def xy_downsample(
+    x,
+    y,
+    uppx,
+
+    x_spacer: float = 0.5,
+
+) -> tuple[np.ndarray, np.ndarray]:
+
+    # downsample whenever more then 1 pixels per datum can be shown.
+    # always refresh data bounds until we get diffing
+    # working properly, see above..
+    bins, x, y = ds_m4(
+        x,
+        y,
+        uppx,
+    )
+
+    # flatten output to 1d arrays suitable for path-graphics generation.
+    x = np.broadcast_to(x[:, None], y.shape)
+    x = (x + np.array(
+        [-x_spacer, 0, 0, x_spacer]
+    )).flatten()
+    y = y.flatten()
+
+    return x, y
+
+
+@njit(
+    # TODO: for now need to construct this manually for readonly arrays, see
+    # https://github.com/numba/numba/issues/4511
+    # ntypes.tuple((float64[:], float64[:], float64[:]))(
+    #     numba_ohlc_dtype[::1],  # contiguous
+    #     int64,
+    #     optional(float64),
+    # ),
+    nogil=True
+)
+def path_arrays_from_ohlc(
+    data: np.ndarray,
+    start: int64,
+    bar_gap: float64 = 0.43,
+
+) -> np.ndarray:
+    '''
+    Generate an array of lines objects from input ohlc data.
+
+    '''
+    size = int(data.shape[0] * 6)
+
+    x = np.zeros(
+        # data,
+        shape=size,
+        dtype=float64,
+    )
+    y, c = x.copy(), x.copy()
+
+    # TODO: report bug for assert @
+    # /home/goodboy/repos/piker/env/lib/python3.8/site-packages/numba/core/typing/builtins.py:991
+    for i, q in enumerate(data[start:], start):
+
+        # TODO: ask numba why this doesn't work..
+        # open, high, low, close, index = q[
+        #     ['open', 'high', 'low', 'close', 'index']]
+
+        open = q['open']
+        high = q['high']
+        low = q['low']
+        close = q['close']
+        index = float64(q['index'])
+
+        istart = i * 6
+        istop = istart + 6
+
+        # x,y detail the 6 points which connect all vertexes of a ohlc bar
+        x[istart:istop] = (
+            index - bar_gap,
+            index,
+            index,
+            index,
+            index,
+            index + bar_gap,
+        )
+        y[istart:istop] = (
+            open,
+            open,
+            low,
+            high,
+            close,
+            close,
+        )
+
+        # specifies that the first edge is never connected to the
+        # prior bars last edge thus providing a small "gap"/"space"
+        # between bars determined by ``bar_gap``.
+        c[istart:istop] = (1, 1, 1, 1, 1, 0)
+
+    return x, y, c
+
+
+def gen_ohlc_qpath(
+    r: Renderer,
+    data: np.ndarray,
+    array_key: str,  # we ignore this
+    vr: tuple[int, int],
+
+    start: int = 0,  # XXX: do we need this?
+    # 0.5 is no overlap between arms, 1.0 is full overlap
+    w: float = 0.43,
+
+) -> QtGui.QPainterPath:
+    '''
+    More or less direct proxy to ``path_arrays_from_ohlc()``
+    but with closed in kwargs for line spacing.
+
+    '''
+    x, y, c = path_arrays_from_ohlc(
+        data,
+        start,
+        bar_gap=w,
+    )
+    return x, y, c
+
+
+def ohlc_to_line(
+    ohlc_shm: ShmArray,
+    data_field: str,
+    fields: list[str] = ['open', 'high', 'low', 'close']
+
+) -> tuple[
+    np.ndarray,
+    np.ndarray,
+]:
+    '''
+    Convert an input struct-array holding OHLC samples into a pair of
+    flattened x, y arrays with the same size (datums wise) as the source
+    data.
+
+    '''
+    y_out = ohlc_shm.ustruct(fields)
+    first = ohlc_shm._first.value
+    last = ohlc_shm._last.value
+
+    # write pushed data to flattened copy
+    y_out[first:last] = rfn.structured_to_unstructured(
+        ohlc_shm.array[fields]
+    )
+
+    # generate an flat-interpolated x-domain
+    x_out = (
+        np.broadcast_to(
+            ohlc_shm._array['index'][:, None],
+            (
+                ohlc_shm._array.size,
+                # 4,  # only ohlc
+                y_out.shape[1],
+            ),
+        ) + np.array([-0.5, 0, 0, 0.5])
+    )
+    assert y_out.any()
+
+    return (
+        x_out,
+        y_out,
+    )
+
+
+def to_step_format(
+    shm: ShmArray,
+    data_field: str,
+    index_field: str = 'index',
+
+) -> tuple[int, np.ndarray, np.ndarray]:
+    '''
+    Convert an input 1d shm array to a "step array" format
+    for use by path graphics generation.
+
+    '''
+    i = shm._array['index'].copy()
+    out = shm._array[data_field].copy()
+
+    x_out = np.broadcast_to(
+        i[:, None],
+        (i.size, 2),
+    ) + np.array([-0.5, 0.5])
+
+    y_out = np.empty((len(out), 2), dtype=out.dtype)
+    y_out[:] = out[:, np.newaxis]
+
+    # start y at origin level
+    y_out[0, 0] = 0
+    return x_out, y_out
diff --git a/piker/ui/order_mode.py b/piker/ui/order_mode.py
index 3e230b71..a86fe816 100644
--- a/piker/ui/order_mode.py
+++ b/piker/ui/order_mode.py
@@ -873,7 +873,9 @@ async def process_trades_and_update_ui(
                 mode.lines.remove_line(uuid=oid)
 
         # each clearing tick is responded individually
-        elif resp in ('broker_filled',):
+        elif resp in (
+            'broker_filled',
+        ):
 
             known_order = book._sent_orders.get(oid)
             if not known_order: