Use `get_fonts()`, add `show_txt` flag to gap annots

Switch `.tsp._annotate.markup_gaps()` to use new
`.ui._style.get_fonts()` API for font size calc on client side and add
optional `show_txt: bool` flag to toggle gap duration labels (with
default `False`).

Also,
- replace `sgn` checks with named bools: `up_gap`, `down_gap`
- use `small_font.px_size - 1` for gap label font sizing
- wrap text creation in `if show_txt:` block
- update IPC handler to use `get_fonts()` vs direct `_font` import

(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code

piker/tsp/_annotate.py

@@ -30,7 +30,7 @@ import tractor
 
 from piker.data._formatters import BGM
 from piker.storage import log
-# from piker.ui._style import _font
+from piker.ui._style import get_fonts
 
 if TYPE_CHECKING:
     from piker.ui._remote_ctl import AnnotCtl
@@ -88,6 +88,10 @@ async def markup_gaps(
     wdts: pl.DataFrame,
     gaps: pl.DataFrame,
 
+    # XXX, switch on to see txt showing a "humanized" label of each
+    # gap's duration.
+    show_txt: bool = False,
+
 ) -> dict[int, dict]:
     '''
     Remote annotate time-gaps in a dt-fielded ts (normally OHLC)
@@ -202,6 +206,10 @@ async def markup_gaps(
 
         diff: float = cls - opn
         sgn: float = copysign(1, diff)
+        up_gap: bool = sgn == -1
+        down_gap: bool = sgn == 1
+        flat: bool = sgn == 0
+
         color: str = 'dad_blue'
         # TODO? mks more sense to have up/down coloring?
         # color: str = {
@@ -233,7 +241,7 @@ async def markup_gaps(
         assert aid
         aids[aid] = rect_kwargs
         direction: str = (
-            'down' if sgn == 1
+            'down' if down_gap
             else 'up'
         )
         # TODO! mk this a `msgspec.Struct` which we deserialize
@@ -261,19 +269,21 @@ async def markup_gaps(
         )
 
         # add duration label to RHS of arrow
-        if sgn == -1:  # up-gap
-            anchor = (0, 0)  # XXX, i dun get dese dims.. XD
-        else:  # down-gap
+        if up_gap:
+            anchor = (0, 0)
+            # ^XXX? i dun get dese dims.. XD
+        elif down_gap:
             anchor = (0, 1)  # XXX y, x?
+        else:  # no-gap?
+            assert flat
+            anchor = (0, 0)  # up from bottom
 
-        # ?TODO? why returning -1 !?
-        # [ ] use conf.toml value instead!
-        #
-        # font_size: int = _font.font.pixelSize() - 10
-        # await tractor.pause()
-        # assert isinstance(font_size, int)
-        font_size = None
+        # use a slightly smaller font for gap label txt.
+        font, small_font = get_fonts()
+        font_size: int = small_font.px_size - 1
+        assert isinstance(font_size, int)
 
+        if show_txt:
             text_aid: int = await actl.add_text(
                 fqme=fqme,
                 timeframe=timeframe,

piker/ui/_remote_ctl.py

@@ -407,8 +407,9 @@ async def serve_rc_annots(
                 # apply font size (default to DpiAwareFont if not
                 # provided)
                 if font_size is None:
-                    from ._style import _font
-                    font_size =  _font.font.pixelSize() - 3
+                    from ._style import get_fonts
+                    font, font_small = get_fonts()
+                    font_size =  font_small.px_size - 1
 
                 qfont: QFont = text_item.textItem.font()
                 qfont.setPixelSize(font_size)

piker/ui/_style.py

@@ -107,7 +107,22 @@ class DpiAwareFont:
 
     @property
     def px_size(self) -> int:
-        return self._qfont.pixelSize()
+        size: int = self._qfont.pixelSize()
+
+        # XXX, when no Qt app has been spawned this will always be
+        # invalid..
+        # SO, just return any conf.toml value.
+        if size == -1:
+            if (conf_size := self._font_size) is None:
+                raise ValueError(
+                    f'No valid `{type(_font).__name__}.px_size` set?\n'
+                    f'\n'
+                    f'-> `ui.font_size` is NOT set in `conf.toml`\n'
+                    f'-> no Qt app is active ??\n'
+                )
+            return conf_size
+
+        return size
 
     def configure_to_dpi(self, screen: QtGui.QScreen | None = None):
         '''
@@ -221,6 +236,20 @@ def _config_fonts_to_screen() -> None:
     _font_small.configure_to_dpi()
 
 
+def get_fonts() -> tuple[
+    DpiAwareFont,
+    DpiAwareFont,
+]:
+    '''
+    Get the singleton font pair (of instances) from which all other
+    UI/UX should be "scaled around".
+
+    See `DpiAwareFont` for (internal) deats.
+
+    '''
+    return _font, _font_small
+
+
 # TODO: re-compute font size when main widget switches screens?
 # https://forum.qt.io/topic/54136/how-do-i-get-the-qscreen-my-widget-is-on-qapplication-desktop-screen-returns-a-qwidget-and-qobject_cast-qscreen-returns-null/3