Improved DPI Scaling on Windows and Fixed related Bugs

changes/2155.bugfix.rst

@@ -0,0 +1 @@
+Bugs affecting DPI scaling on Windows were fixed.

winforms/src/toga_winforms/app.py

@@ -2,9 +2,10 @@
 import re
 import sys
 import threading
-from ctypes import windll
+from ctypes import c_bool, c_void_p, windll
 
 import System.Windows.Forms as WinForms
+from Microsoft.Win32 import SystemEvents
 from System import Environment, Threading
 from System.Media import SystemSounds
 from System.Net import SecurityProtocolType, ServicePointManager
@@ -16,6 +17,7 @@
 from .keys import toga_to_winforms_key
 from .libs.proactor import WinformsProactorEventLoop
 from .libs.wrapper import WeakrefCallable
+from .widgets.base import Scalable
 from .window import Window
 
 
@@ -32,9 +34,43 @@ def winforms_FormClosing(self, sender, event):
                 event.Cancel = True
 
 
-class App:
+class App(Scalable):
     _MAIN_WINDOW_CLASS = MainWindow
 
+    # ------------------- Set the DPI Awareness mode for the process -------------------
+    # This needs to be done at the earliest and doing this in __init__() or
+    # in create() doesn't work
+    #
+    # Check the version of windows and make sure we are setting the DPI mode
+    # with the most up to date API
+    # Windows Versioning Check Sources : https://www.lifewire.com/windows-version-numbers-2625171
+    # and https://docs.microsoft.com/en-us/windows/release-information/
+    win_version = Environment.OSVersion.Version
+    if win_version.Major >= 6:  # Checks for Windows Vista or later
+        # Represents Windows 8.1 up to Windows 10 before Build 1703 which should use
+        # SetProcessDpiAwareness(True)
+        if (win_version.Major == 6 and win_version.Minor == 3) or (
+            win_version.Major == 10 and win_version.Build < 15063
+        ):
+            windll.shcore.SetProcessDpiAwareness(True)
+            print(
+                "WARNING: Your Windows version doesn't support DPI-independent rendering.  "
+                "We recommend you upgrade to at least Windows 10 Build 1703."
+            )
+        # Represents Windows 10 Build 1703 and beyond which should use
+        # SetProcessDpiAwarenessContext(-4) for DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2
+        # Valid values: https://learn.microsoft.com/en-us/windows/win32/hidpi/dpi-awareness-context
+        elif win_version.Major == 10 and win_version.Build >= 15063:
+            windll.user32.SetProcessDpiAwarenessContext.restype = c_bool
+            windll.user32.SetProcessDpiAwarenessContext.argtypes = [c_void_p]
+            # SetProcessDpiAwarenessContext returns False on Failure
+            if not windll.user32.SetProcessDpiAwarenessContext(-4):
+                print("WARNING: Failed to set the DPI Awareness mode for the app.")
+        # Any other version of windows should use SetProcessDPIAware()
+        else:
+            windll.user32.SetProcessDPIAware()
+    # ----------------------------------------------------------------------------------
+
     def __init__(self, interface):
         self.interface = interface
         self.interface._impl = self
@@ -61,33 +97,13 @@ def create(self):
         self.app_context = WinForms.ApplicationContext()
         self.app_dispatcher = Dispatcher.CurrentDispatcher
 
-        # Check the version of windows and make sure we are setting the DPI mode
-        # with the most up to date API
-        # Windows Versioning Check Sources : https://www.lifewire.com/windows-version-numbers-2625171
-        # and https://docs.microsoft.com/en-us/windows/release-information/
-        win_version = Environment.OSVersion.Version
-        if win_version.Major >= 6:  # Checks for Windows Vista or later
-            # Represents Windows 8.1 up to Windows 10 before Build 1703 which should use
-            # SetProcessDpiAwareness(True)
-            if (win_version.Major == 6 and win_version.Minor == 3) or (
-                win_version.Major == 10 and win_version.Build < 15063
-            ):
-                windll.shcore.SetProcessDpiAwareness(True)
-                print(
-                    "WARNING: Your Windows version doesn't support DPI-independent rendering.  "
-                    "We recommend you upgrade to at least Windows 10 Build 1703."
-                )
-            # Represents Windows 10 Build 1703 and beyond which should use
-            # SetProcessDpiAwarenessContext(-2)
-            elif win_version.Major == 10 and win_version.Build >= 15063:
-                windll.user32.SetProcessDpiAwarenessContext(-2)
-            # Any other version of windows should use SetProcessDPIAware()
-            else:
-                windll.user32.SetProcessDPIAware()
-
+        # These are required for properly setting up DPI mode
         self.native.EnableVisualStyles()
         self.native.SetCompatibleTextRenderingDefault(False)
 
+        # Register the DisplaySettingsChanged event handler
+        SystemEvents.DisplaySettingsChanged += self.winforms_DisplaySettingsChanged
+
         # Ensure that TLS1.2 and TLS1.3 are enabled for HTTPS connections.
         # For some reason, some Windows installs have these protocols
         # turned off by default. SSL3, TLS1.0 and TLS1.1 are *not* enabled
@@ -332,6 +348,11 @@ def hide_cursor(self):
             WinForms.Cursor.Hide()
         self._cursor_visible = False
 
+    def winforms_DisplaySettingsChanged(self, sender, event):
+        self.update_scale()
+        for window in self.interface.windows:
+            window.content.refresh()
+
 
 class DocumentApp(App):
     def _create_app_commands(self):

winforms/src/toga_winforms/container.py

@@ -6,7 +6,6 @@
 
 class Container(Scalable):
     def __init__(self, native_parent):
-        self.init_scale(native_parent)
         self.native_parent = native_parent
         self.native_width = self.native_height = 0
         self.content = None

winforms/src/toga_winforms/widgets/base.py

@@ -1,4 +1,5 @@
 from abc import ABC, abstractmethod
+from ctypes import byref, c_void_p, windll, wintypes
 from decimal import ROUND_HALF_EVEN, ROUND_UP, Decimal
 
 from System.Drawing import (
@@ -7,6 +8,7 @@
     Size,
     SystemColors,
 )
+from System.Windows.Forms import Screen
 from travertino.size import at_least
 
 from toga.colors import TRANSPARENT
@@ -16,19 +18,36 @@
 class Scalable:
     SCALE_DEFAULT_ROUNDING = ROUND_HALF_EVEN
 
-    def init_scale(self, native):
-        self.dpi_scale = native.CreateGraphics().DpiX / 96
+    def update_scale(self):
+        screen = Screen.PrimaryScreen
+        screen_rect = wintypes.RECT(
+            screen.Bounds.Left,
+            screen.Bounds.Top,
+            screen.Bounds.Right,
+            screen.Bounds.Bottom,
+        )
+        windll.user32.MonitorFromRect.restype = c_void_p
+        windll.user32.MonitorFromRect.argtypes = [wintypes.RECT, wintypes.DWORD]
+        # MONITOR_DEFAULTTONEAREST = 2
+        hMonitor = windll.user32.MonitorFromRect(screen_rect, 2)
+        pScale = wintypes.UINT()
+        windll.shcore.GetScaleFactorForMonitor(c_void_p(hMonitor), byref(pScale))
+        Scalable.dpi_scale = pScale.value / 100
 
     # Convert CSS pixels to native pixels
     def scale_in(self, value, rounding=SCALE_DEFAULT_ROUNDING):
-        return self.scale_round(value * self.dpi_scale, rounding)
+        if not hasattr(Scalable, "dpi_scale"):
+            self.update_scale()
+        return self.scale_round(value * Scalable.dpi_scale, rounding)
 
     # Convert native pixels to CSS pixels
     def scale_out(self, value, rounding=SCALE_DEFAULT_ROUNDING):
+        if not hasattr(Scalable, "dpi_scale"):
+            self.update_scale()
         if isinstance(value, at_least):
             return at_least(self.scale_out(value.value, rounding))
         else:
-            return self.scale_round(value / self.dpi_scale, rounding)
+            return self.scale_round(value / Scalable.dpi_scale, rounding)
 
     def scale_round(self, value, rounding):
         if rounding is None:
@@ -49,7 +68,6 @@ def __init__(self, interface):
         self._container = None
         self.native = None
         self.create()
-        self.init_scale(self.native)
         self.interface.style.reapply()
 
     @abstractmethod

winforms/src/toga_winforms/window.py

@@ -22,7 +22,6 @@ def __init__(self, interface, title, position, size):
         self.native = WinForms.Form()
         self.native.FormClosing += WeakrefCallable(self.winforms_FormClosing)
         super().__init__(self.native)
-        self.init_scale(self.native)
 
         self.native.MinimizeBox = self.interface.minimizable
         self.native.MaximizeBox = self.interface.resizable