Fix set_size_inches on HiDPI screens

This passes physical pixels to the backend, as it will be more accurate
due to the int-cast.

Fixes matplotlib#21090

Author: QuLogic

lib/matplotlib/backend_bases.py

@@ -1762,7 +1762,12 @@ def blit(self, bbox=None):
         """Blit the canvas in bbox (default entire canvas)."""
 
     def resize(self, w, h):
-        """Set the canvas size in pixels."""
+        """
+        UNUSED: Set the canvas size in pixels.
+
+        Certain backends may implement a similar method internally, but this is
+        not a requirement of, nor is it used by, Matplotlib itself.
+        """
 
     def draw_event(self, renderer):
         """Pass a `DrawEvent` to all functions connected to ``draw_event``."""
@@ -2815,7 +2820,7 @@ def full_screen_toggle(self):
         pass
 
     def resize(self, w, h):
-        """For GUI backends, resize the window (in pixels)."""
+        """For GUI backends, resize the window (in physical pixels)."""
 
     @_api.deprecated(
         "3.4", alternative="self.canvas.callbacks.process(event.name, event)")

lib/matplotlib/backends/backend_gtk3.py

@@ -421,6 +421,8 @@ def set_window_title(self, title):
 
     def resize(self, width, height):
         """Set the canvas size in pixels."""
+        width = int(width / self.canvas.device_pixel_ratio)
+        height = int(height / self.canvas.device_pixel_ratio)
         if self.toolbar:
             toolbar_size = self.toolbar.size_request()
             height += toolbar_size.height

lib/matplotlib/backends/backend_gtk4.py

@@ -373,6 +373,8 @@ def set_window_title(self, title):
 
     def resize(self, width, height):
         """Set the canvas size in pixels."""
+        width = int(width / self.canvas.device_pixel_ratio)
+        height = int(height / self.canvas.device_pixel_ratio)
         if self.toolbar:
             min_size, nat_size = self.toolbar.get_preferred_size()
             height += nat_size.height

lib/matplotlib/backends/backend_qt.py

@@ -589,8 +589,10 @@ def _get_toolbar(self, canvas, parent):
         return toolbar
 
     def resize(self, width, height):
-        # these are Qt methods so they return sizes in 'virtual' pixels
-        # so we do not need to worry about dpi scaling here.
+        # The Qt methods return sizes in 'virtual' pixels so we do need to
+        # rescale from physical to logical pixels.
+        width = int(width / self.canvas.device_pixel_ratio)
+        height = int(height / self.canvas.device_pixel_ratio)
         extra_width = self.window.width() - self.canvas.width()
         extra_height = self.window.height() - self.canvas.height()
         self.canvas.resize(width, height)

lib/matplotlib/figure.py

@@ -2658,10 +2658,9 @@ def set_size_inches(self, w, h=None, forward=True):
         if forward:
             canvas = getattr(self, 'canvas')
             if canvas is not None:
-                dpi_ratio = getattr(canvas, '_dpi_ratio', 1)
                 manager = getattr(canvas, 'manager', None)
                 if manager is not None:
-                    manager.resize(*(size * self.dpi / dpi_ratio).astype(int))
+                    manager.resize(*(size * self.dpi).astype(int))
         self.stale = True
 
     def get_size_inches(self):