Attempt to calculate font size by DPI

piker/ui/_chart.py

@@ -36,7 +36,7 @@ from ..data import (
     maybe_open_shm_array,
 )
 from ..log import get_logger
-from ._exec import run_qtractor
+from ._exec import run_qtractor, current_screen
 from ._interaction import ChartView
 from .. import fsp
 
@@ -233,7 +233,10 @@ class LinkedSplitCharts(QtGui.QWidget):
         cpw = ChartPlotWidget(
             array=array,
             parent=self.splitter,
-            axisItems={'bottom': xaxis, 'right': PriceAxis()},
+            axisItems={
+                'bottom': xaxis,
+                'right': PriceAxis(linked_charts=self)
+            },
             viewBox=cv,
             cursor=self._ch,
             **cpw_kwargs,
@@ -688,6 +691,21 @@ async def _async_main(
     """
     chart_app = widgets['main']
 
+    screen = current_screen()
+
+    from ._style import configure_font_to_dpi
+    print(
+        f'screen: {screen.name()} {screen.size()}')
+
+    configure_font_to_dpi(screen)
+
+    # from ._exec import get_screen
+    # screen = get_screen(chart_app.geometry().bottomRight())
+
+    # XXX: bug zone if you try to ctl-c after this we get hangs again?
+    # wtf...
+    # await tractor.breakpoint()
+
     # historical data fetch
     brokermod = brokers.get_brokermod(brokername)
 

piker/ui/_exec.py

@@ -16,12 +16,22 @@ from PyQt5.QtCore import (
     pyqtRemoveInputHook, Qt, QCoreApplication
 )
 import qdarkstyle
-
 import trio
 import tractor
 from outcome import Error
 
 
+# singleton app per actor
+_qt_app: QtGui.QApplication = None
+_qt_win: QtGui.QMainWindow = None
+
+
+def current_screen() -> QtGui.QScreen:
+
+    global _qt_win, _qt_app
+    return _qt_app.screenAt(_qt_win.centralWidget().geometry().center())
+
+
 # Proper high DPI scaling is available in Qt >= 5.6.0. This attibute
 # must be set before creating the application
 if hasattr(Qt, 'AA_EnableHighDpiScaling'):
@@ -62,6 +72,10 @@ def run_qtractor(
     # currently seem tricky..
     app.setQuitOnLastWindowClosed(False)
 
+    # set global app singleton
+    global _qt_app
+    _qt_app = app
+
     # This code is from Nathaniel, and I quote:
     # "This is substantially faster than using a signal... for some
     # reason Qt signal dispatch is really slow (and relies on events
@@ -84,10 +98,13 @@ def run_qtractor(
         app.postEvent(reenter, event)
 
     def done_callback(outcome):
+
         print(f"Outcome: {outcome}")
+
         if isinstance(outcome, Error):
             exc = outcome.error
             traceback.print_exception(type(exc), exc, exc.__traceback__)
+
         app.quit()
 
     # load dark theme
@@ -125,6 +142,12 @@ def run_qtractor(
 
     window.main_widget = main_widget
     window.setCentralWidget(instance)
+
+    # store global ref
+    # set global app singleton
+    global _qt_win
+    _qt_win = window
+
     # actually render to screen
     window.show()
     app.exec_()

piker/ui/_style.py

@@ -5,19 +5,54 @@ import pyqtgraph as pg
 from PyQt5 import QtGui
 from qdarkstyle.palette import DarkPalette
 
+from ..log import get_logger
+
+log = get_logger(__name__)
 
 # chart-wide font
-_font = QtGui.QFont("Hack")
+# font size 6px / 53 dpi (3x scaled down on 4k hidpi)
+_font_inches_we_like = 6 / 53
+
 # use pixel size to be cross-resolution compatible?
-_font.setPixelSize(6)
+_font = QtGui.QFont("Hack")
+_font.setPixelSize(6)  # default
 
-# TODO: use QScreen to determine the same physical font size
-# on screen despite different displays?
-# PyQt docs: https://doc.qt.io/qtforpython/PySide2/QtGui/QScreen.html
-#   - supposedly it's ``from QtGui import QScreen``
-# Qt forums: https://forum.qt.io/topic/43625/point-sizes-are-they-reliable/4
+# _physical_font_height_in = 1/6  # inches
+_font._fm = QtGui.QFontMetrics(_font)
 
-_i3_rgba = QtGui.QColor.fromRgbF(*[0.14]*3 + [1])
+# 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
+
+
+def configure_font_to_dpi(screen: QtGui.QScreen):
+    """Set an appropriately sized font size depending on the screen DPI.
+
+    If we end up needing to generalize this more here are some resources:
+
+    - https://stackoverflow.com/questions/42141354/convert-pixel-size-to-point-size-for-fonts-on-multiple-platforms
+    - https://stackoverflow.com/questions/25761556/qt5-font-rendering-different-on-various-platforms/25929628#25929628
+    - https://doc.qt.io/qt-5/highdpi.html
+    - https://stackoverflow.com/questions/20464814/changing-dpi-scaling-size-of-display-make-qt-applications-font-size-get-rendere
+    - https://stackoverflow.com/a/20465247
+    - https://doc.qt.io/archives/qt-4.8/qfontmetrics.html#width
+    - 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
+    - https://forum.qt.io/topic/43625/point-sizes-are-they-reliable/4
+
+    Also, see the script in ``snippets/qt_screen_info.py``.
+
+    """
+    dpi = screen.physicalDotsPerInch()
+    font_size = round(_font_inches_we_like * dpi)
+    log.info(
+        f"\nscreen:{screen.name()} with DPI: {dpi}"
+        f"\nbest font size is {font_size}\n"
+    )
+    global _font
+    _font.setPixelSize(font_size)
+    return _font
+
+
+# _i3_rgba = QtGui.QColor.fromRgbF(*[0.14]*3 + [1])
 
 # splitter widget config
 _xaxis_at = 'bottom'