Rework charting internals for real-time plotting

`pg.PlotCurveItem.setData()` is normally used for real-time updates to
curves and takes in a whole new array of data to graphics.
It makes sense to stick with this interface especially if
the current datum graphic will originally be drawn from tick quotes and
later filled in when bars data is available (eg. IB has this option in
TWS charts for volume). Additionally, having a data feed api where the push
process/task can write to shared memory and the UI task(s) can read from
that space is ideal. It allows for indicator and algo calculations to be
run in parallel (via actors) with initial price draw instructions
such that plotting of downstream metrics can be "pipelined" into the
chart UI's render loop. This essentially makes the chart UI async
programmable from multiple remote processes (or at least that's the
goal).

Some details:
- Only store a single ref to the source array data on the
  `LinkedSplitCharts`.  There should only be one reference since the main
  relation is **that** x-time aligned sequence.
- Add `LinkedSplitCharts.update_from_quote()` which takes in a quote
  dict and updates the OHLC array from it's contents.
- Add `ChartPlotWidget.update_from_array()` method to trigger graphics
  updates per chart with consideration for overlay curves.

piker/ui/_axes.py

@@ -33,14 +33,13 @@ class PriceAxis(pg.AxisItem):
     #     ]
 
 
-class FromTimeFieldDateAxis(pg.AxisItem):
+class DynamicDateAxis(pg.AxisItem):
     tick_tpl = {'D1': '%Y-%b-%d'}
 
-    def __init__(self, splitter, *args, **kwargs):
+    def __init__(self, linked_charts, *args, **kwargs):
         super().__init__(*args, **kwargs)
-        self.splitter = splitter
+        self.linked_charts = linked_charts
         self.setTickFont(_font)
-        # self.quotes_count = len(self.splitter.chart._array) - 1
 
         # default styling
         self.setStyle(
@@ -57,12 +56,12 @@ class FromTimeFieldDateAxis(pg.AxisItem):
         # strings = super().tickStrings(values, scale, spacing)
         s_period = 'D1'
         strings = []
-        quotes_count = len(self.splitter.chart._array) - 1
+        bars = self.linked_charts._array
+        quotes_count = len(bars) - 1
 
         for ibar in values:
             if ibar > quotes_count:
                 return strings
-            bars = self.splitter.chart._array
             dt_tick = fromtimestamp(bars[int(ibar)].time)
             strings.append(
                 dt_tick.strftime(self.tick_tpl[s_period])
@@ -144,7 +143,7 @@ class XAxisLabel(AxisLabel):
     def tick_to_string(self, tick_pos):
         # TODO: change to actual period
         tpl = self.parent.tick_tpl['D1']
-        bars = self.parent.splitter.chart._array
+        bars = self.parent.linked_charts._array
         if tick_pos > len(bars):
             return 'Unknown Time'
         return fromtimestamp(bars[round(tick_pos)].time).strftime(tpl)
@@ -173,7 +172,7 @@ class YAxisLabel(AxisLabel):
         return ('{: ,.%df}' % self.digits).format(tick_pos).replace(',', ' ')
 
     def boundingRect(self):  # noqa
-        return QtCore.QRectF(0, 0, 80, 40)
+        return QtCore.QRectF(0, 0, 100, 40)
 
     def update_label(self, evt_post, point_view):
         self.label_str = self.tick_to_string(point_view.y())

piker/ui/_chart.py

@@ -1,6 +1,8 @@
 """
 High level Qt chart widgets.
 """
+from typing import List, Optional
+
 import trio
 import numpy as np
 import pyqtgraph as pg
@@ -8,12 +10,12 @@ from pyqtgraph import functions as fn
 from PyQt5 import QtCore, QtGui
 
 from ._axes import (
-    FromTimeFieldDateAxis,
+    DynamicDateAxis,
     PriceAxis,
 )
 from ._graphics import CrossHairItem, ChartType
 from ._style import _xaxis_at
-from ._source import Symbol, ohlc_zeros
+from ._source import Symbol
 
 
 # margins
@@ -85,9 +87,13 @@ class ChartSpace(QtGui.QWidget):
 
 
 class LinkedSplitCharts(QtGui.QWidget):
-    """Widget that holds a price chart plus indicators separated by splitters.
+    """Widget that holds a central chart plus derived
-    """
+    subcharts computed from the original data set apart
+    by splitters for resizing.
 
+    A single internal references to the data is maintained
+    for each chart and can be updated externally.
+    """
     long_pen = pg.mkPen('#006000')
     long_brush = pg.mkBrush('#00ff00')
     short_pen = pg.mkPen('#600000')
@@ -98,13 +104,21 @@ class LinkedSplitCharts(QtGui.QWidget):
     def __init__(self):
         super().__init__()
         self.signals_visible = False
+
+        # main data source
+        self._array = None
+
+        self._ch = None  # crosshair graphics
+        self._index = 0
+
+        self.chart = None  # main (ohlc) chart
         self.indicators = []
 
-        self.xaxis = FromTimeFieldDateAxis(orientation='bottom', splitter=self)
+        self.xaxis = DynamicDateAxis(
-        # self.xaxis = pg.DateAxisItem()
+            orientation='bottom', linked_charts=self)
 
-        self.xaxis_ind = FromTimeFieldDateAxis(
+        self.xaxis_ind = DynamicDateAxis(
-            orientation='bottom', splitter=self)
+            orientation='bottom', linked_charts=self)
 
         if _xaxis_at == 'bottom':
             self.xaxis.setStyle(showValues=False)
@@ -119,24 +133,36 @@ class LinkedSplitCharts(QtGui.QWidget):
 
         self.layout.addWidget(self.splitter)
 
-    def _update_sizes(self):
+    def set_split_sizes(
-        min_h_ind = int(self.height() * 0.2 / len(self.indicators))
+        self,
-        sizes = [int(self.height() * 0.8)]
+        prop: float = 0.2
+    ) -> None:
+        """Set the proportion of space allocated for linked subcharts.
+        """
+        major = 1 - prop
+        # 20% allocated to consumer subcharts
+        min_h_ind = int(self.height() * prop / len(self.indicators))
+        sizes = [int(self.height() * major)]
         sizes.extend([min_h_ind] * len(self.indicators))
         self.splitter.setSizes(sizes)  # , int(self.height()*0.2)
 
     def plot(
         self,
         symbol: Symbol,
-        data: np.ndarray,
+        array: np.ndarray,
+        ohlc: bool = True,
     ):
-        """Start up and show price chart and all registered indicators.
+        """Start up and show main (price) chart and all linked subcharts.
         """
         self.digits = symbol.digits()
 
+        # XXX: this may eventually be a view onto shared mem
+        # or some higher level type / API
+        self._array = array
+
         cv = ChartView()
         self.chart = ChartPlotWidget(
-            split_charts=self,
+            linked_charts=self,
             parent=self.splitter,
             axisItems={'bottom': self.xaxis, 'right': PriceAxis()},
             viewBox=cv,
@@ -144,52 +170,96 @@ class LinkedSplitCharts(QtGui.QWidget):
         )
         # TODO: ``pyqtgraph`` doesn't pass through a parent to the
         # ``PlotItem`` by default; maybe we should PR this in?
-        cv.splitter_widget = self
+        cv.linked_charts = self
-        self.chart.plotItem.vb.splitter_widget = self
+        self.chart.plotItem.vb.linked_charts = self
 
         self.chart.getPlotItem().setContentsMargins(*CHART_MARGINS)
         self.chart.setFrameStyle(QtGui.QFrame.StyledPanel | QtGui.QFrame.Plain)
 
-        self.chart.draw_ohlc(data)
+        if ohlc:
+            self.chart.draw_ohlc(array)
+        else:
+            raise NotImplementedError(
+                "Only OHLC linked charts are supported currently"
+            )
 
         # TODO: this is where we would load an indicator chain
         # XXX: note, if this isn't index aligned with
         # the source data the chart will go haywire.
-        inds = [data.open]
+        inds = [('open', lambda a: a.close)]
 
-        for d in inds:
+        for name, func in inds:
             cv = ChartView()
             ind_chart = ChartPlotWidget(
-                split_charts=self,
+                linked_charts=self,
                 parent=self.splitter,
                 axisItems={'bottom': self.xaxis_ind, 'right': PriceAxis()},
                 # axisItems={'top': self.xaxis_ind, 'right': PriceAxis()},
                 viewBox=cv,
             )
-            cv.splitter_widget = self
+            # this name will be used to register the primary
-            self.chart.plotItem.vb.splitter_widget = self
+            # graphics curve managed by the subchart
+            ind_chart.name = name
+            cv.linked_charts = self
+            self.chart.plotItem.vb.linked_charts = self
 
             ind_chart.setFrameStyle(
                 QtGui.QFrame.StyledPanel | QtGui.QFrame.Plain
             )
             ind_chart.getPlotItem().setContentsMargins(*CHART_MARGINS)
             # self.splitter.addWidget(ind_chart)
-            self.indicators.append((ind_chart, d))
+
+            # compute historical subchart values from input array
+            data = func(array)
+            self.indicators.append((ind_chart, func))
 
             # link chart x-axis to main quotes chart
             ind_chart.setXLink(self.chart)
 
-            # XXX: never do this lol
+            # draw curve graphics
-            # ind.setAspectLocked(1)
+            ind_chart.draw_curve(data, name)
-            ind_chart.draw_curve(d)
 
-        self._update_sizes()
+        self.set_split_sizes()
 
-        ch = CrossHairItem(
+        ch = self._ch = CrossHairItem(
-            self.chart, [_ind for _ind, d in self.indicators], self.digits
+            self.chart,
+            [_ind for _ind, d in self.indicators],
+            self.digits
         )
         self.chart.addItem(ch)
 
+    def update_from_quote(
+        self,
+        quote: dict
+    ) -> List[pg.GraphicsObject]:
+        """Update all linked chart graphics with a new quote
+        datum.
+
+        Return the modified graphics objects in a list.
+        """
+        # TODO: eventually we'll want to update bid/ask labels and other
+        # data as subscribed by underlying UI consumers.
+        last = quote['last']
+        current = self._array[-1]
+
+        # update ohlc (I guess we're enforcing this for now?)
+        current['close'] = last
+        current['high'] = max(current['high'], last)
+        current['low'] = min(current['low'], last)
+
+        # update the ohlc sequence graphics chart
+        chart = self.chart
+        # we send a reference to the whole updated array
+        chart.update_from_array(self._array)
+
+        # TODO: the "data" here should really be a function
+        # and it should be managed and computed outside of this UI
+        for chart, func in self.indicators:
+            # process array in entirely every update
+            # TODO: change this for streaming
+            data = func(self._array)
+            chart.update_from_array(data, chart.name)
+
 
 _min_points_to_show = 15
 _min_bars_in_view = 10
@@ -198,12 +268,14 @@ _min_bars_in_view = 10
 class ChartPlotWidget(pg.PlotWidget):
     """``GraphicsView`` subtype containing a single ``PlotItem``.
 
-    Overrides a ``pyqtgraph.PlotWidget`` (a ``GraphicsView`` containing
+    - The added methods allow for plotting OHLC sequences from
+      ``np.recarray``s with appropriate field names.
+    - Overrides a ``pyqtgraph.PlotWidget`` (a ``GraphicsView`` containing
       a single ``PlotItem``) to intercept and and re-emit mouse enter/exit
       events.
 
     (Could be replaced with a ``pg.GraphicsLayoutWidget`` if we
-    eventually want multiple plots managed together).
+    eventually want multiple plots managed together?)
     """
     sig_mouse_leave = QtCore.Signal(object)
     sig_mouse_enter = QtCore.Signal(object)
@@ -213,29 +285,29 @@ class ChartPlotWidget(pg.PlotWidget):
 
     def __init__(
         self,
-        split_charts,
+        linked_charts,
         **kwargs,
         # parent=None,
         # background='default',
         # plotItem=None,
-        # **kargs
     ):
         """Configure chart display settings.
         """
         super().__init__(**kwargs)
+        self.parent = linked_charts
+        # this is the index of that last input array entry and is
+        # updated and used to figure out how many bars are in view
+        self._xlast = 0
+
         # XXX: label setting doesn't seem to work?
         # likely custom graphics need special handling
-
         # label = pg.LabelItem(justify='left')
         # self.addItem(label)
         # label.setText("Yo yoyo")
         # label.setText("<span style='font-size: 12pt'>x=")
-        self.parent = split_charts
 
-        # placeholder for source of data
+        # to be filled in when graphics are rendered
-        self._array = ohlc_zeros(1)
+        # by name
-
-        # to be filled in when data is loaded
         self._graphics = {}
 
         # show only right side axes
@@ -251,40 +323,32 @@ class ChartPlotWidget(pg.PlotWidget):
         self.setCursor(QtCore.Qt.CrossCursor)
 
         # assign callback for rescaling y-axis automatically
-        # based on y-range contents
+        # based on ohlc contents
-        self.sigXRangeChanged.connect(self._update_yrange_limits)
+        self.sigXRangeChanged.connect(self._set_yrange)
 
-    def set_view_limits(self, xfirst, xlast, ymin, ymax):
+    def _set_xlimits(
+        self,
+        xfirst: int,
+        xlast: int
+    ) -> None:
+        """Set view limits (what's shown in the main chart "pane")
+        based on max / min x / y coords.
+        """
         # max_lookahead = _min_points_to_show - _min_bars_in_view
 
         # set panning limits
-        # last = data[-1]['id']
         self.setLimits(
-            # xMin=data[0]['id'],
             xMin=xfirst,
-            # xMax=last + _min_points_to_show - 3,
             xMax=xlast + _min_points_to_show - 3,
             minXRange=_min_points_to_show,
-            # maxYRange=highest-lowest,
-            # yMin=data['low'].min() * 0.98,
-            # yMax=data['high'].max() * 1.02,
-            yMin=ymin * 0.98,
-            yMax=ymax * 1.02,
         )
 
-        # show last 50 points on startup
-        # self.plotItem.vb.setXRange(last - 50, last + 50)
-        self.plotItem.vb.setXRange(xlast - 50, xlast + 50)
-
-        # fit y
-        self._update_yrange_limits()
-
     def bars_range(self):
         """Return a range tuple for the bars present in view.
         """
         vr = self.viewRect()
         lbar = int(vr.left())
-        rbar = int(min(vr.right(), len(self._array) - 1))
+        rbar = int(vr.right())
         return lbar, rbar
 
     def draw_ohlc(
@@ -301,35 +365,55 @@ class ChartPlotWidget(pg.PlotWidget):
         # adds all bar/candle graphics objects for each data point in
         # the np array buffer to be drawn on next render cycle
         graphics.draw_from_data(data)
-        self._graphics['ohlc'] = graphics
+        self._graphics['main'] = graphics
         self.addItem(graphics)
-        self._array = data
 
-        # update view limits
+        # set xrange limits
-        self.set_view_limits(
+        self._xlast = xlast = data[-1]['index']
-            data[0]['index'],
+        self._set_xlimits(data[0]['index'], xlast)
-            data[-1]['index'],
+
-            data['low'].min(),
+        # show last 50 points on startup
-            data['high'].max()
+        self.plotItem.vb.setXRange(xlast - 50, xlast + 50)
-        )
 
         return graphics
 
     def draw_curve(
         self,
         data: np.ndarray,
+        name: Optional[str] = None,
     ) -> None:
         # draw the indicator as a plain curve
         curve = pg.PlotDataItem(data, antialias=True)
         self.addItem(curve)
 
-        # update view limits
+        # register overlay curve with name
-        self.set_view_limits(0, len(data)-1, data.min(), data.max())
+        if not self._graphics and name is None:
-        self._array = data
+            name = 'main'
+        self._graphics[name] = curve
+
+        # set a "startup view"
+        xlast = len(data)-1
+        self._set_xlimits(0, xlast)
+
+        # show last 50 points on startup
+        self.plotItem.vb.setXRange(xlast - 50, xlast + 50)
 
         return curve
 
-    def _update_yrange_limits(self):
+    def update_from_array(
+        self,
+        array: np.ndarray,
+        name: str = 'main',
+    ) -> None:
+        self._xlast = len(array) - 1
+        graphics = self._graphics[name]
+        graphics.setData(array)
+        # update view
+        self._set_yrange()
+
+    def _set_yrange(
+        self,
+    ) -> None:
         """Callback for each y-range update.
 
         This adds auto-scaling like zoom on the scroll wheel such
@@ -343,12 +427,11 @@ class ChartPlotWidget(pg.PlotWidget):
         # self.setAutoVisible(x=False, y=True)
         # self.enableAutoRange(x=False, y=True)
 
+        # figure out x-range bars on screen
         lbar, rbar = self.bars_range()
 
-        # if chart_parent.signals_visible:
+        # TODO: this should be some kind of numpy view api
-        #     chart_parent._show_text_signals(lbar, rbar)
+        bars = self.parent._array[lbar:rbar]
-
-        bars = self._array[lbar:rbar]
         if not len(bars):
             # likely no data loaded yet
             return
@@ -389,7 +472,7 @@ class ChartPlotWidget(pg.PlotWidget):
 
 class ChartView(pg.ViewBox):
     """Price chart view box with interaction behaviors you'd expect from
-    an interactive platform:
+    any interactive platform:
 
         - zoom on mouse scroll that auto fits y-axis
         - no vertical scrolling
@@ -399,12 +482,11 @@ class ChartView(pg.ViewBox):
         self,
         parent=None,
         **kwargs,
-        # invertY=False,
     ):
         super().__init__(parent=parent, **kwargs)
         # disable vertical scrolling
         self.setMouseEnabled(x=True, y=False)
-        self.splitter_widget = None
+        self.linked_charts = None
 
     def wheelEvent(self, ev, axis=None):
         """Override "center-point" location for scrolling.
@@ -422,13 +504,12 @@ class ChartView(pg.ViewBox):
             mask = self.state['mouseEnabled'][:]
 
         # don't zoom more then the min points setting
-        lbar, rbar = self.splitter_widget.chart.bars_range()
+        lbar, rbar = self.linked_charts.chart.bars_range()
-        # breakpoint()
         if ev.delta() >= 0 and rbar - lbar <= _min_points_to_show:
             return
 
         # actual scaling factor
-        s = 1.02 ** (ev.delta() * -1/10)  # self.state['wheelScaleFactor'])
+        s = 1.015 ** (ev.delta() * -1/20)  # self.state['wheelScaleFactor'])
         s = [(None if m is False else s) for m in mask]
 
         # center = pg.Point(
@@ -473,26 +554,27 @@ def main(symbol):
         quotes = from_df(quotes)
 
         # spawn chart
-        splitter_chart = chart_app.load_symbol(symbol, quotes)
+        linked_charts = chart_app.load_symbol(symbol, quotes)
+
+        # make some fake update data
         import itertools
         nums = itertools.cycle([315., 320., 325., 310., 3])
 
         def gen_nums():
-            for i in itertools.count():
+            while True:
-                yield quotes[-1].close + i
+                yield quotes[-1].close + 1
-                yield quotes[-1].close - i
-
-        chart = splitter_chart.chart
 
         nums = gen_nums()
+
+        await trio.sleep(10)
         while True:
-            await trio.sleep(0.1)
             new = next(nums)
             quotes[-1].close = new
-            chart._graphics['ohlc'].update_last_bar({'last': new})
+            # this updates the linked_charts internal array
-
+            # and then passes that array to all subcharts to
-            # LOL this clearly isn't catching edge cases
+            # render downstream graphics
-            chart._update_yrange_limits()
+            linked_charts.update_from_quote({'last': new})
+            await trio.sleep(.1)
 
         await trio.sleep_forever()