gtk3: Fix Cairo backend

QuLogic · QuLogic · commit 6fee86a1cfcf · 2024-06-25T02:10:48.000-04:00
With GTK3, the Cairo surface we get is for the whole window, which means the automatic size inference from matplotlib#22004 gets the wrong size. For the GtkDrawingArea, the Cairo context is aligned and clipped to the widget, so nothing goes out-of-bounds. However, since the Cairo renderer flips the origin using the height in the calculation (which is, for the window, bigger than the drawing widget), everything is drawn lower than it should.
diff --git a/lib/matplotlib/backends/backend_gtk3cairo.py b/lib/matplotlib/backends/backend_gtk3cairo.py
@@ -13,15 +13,19 @@ def on_draw_event(self, widget, ctx):
 
         with (self.toolbar._wait_cursor_for_draw_cm() if self.toolbar
               else nullcontext()):
-            self._renderer.set_context(ctx)
-            scale = self.device_pixel_ratio
-            # Scale physical drawing to logical size.
-            ctx.scale(1 / scale, 1 / scale)
             allocation = self.get_allocation()
+            # Render the background before scaling, as the allocated size here is in
+            # logical pixels.
             Gtk.render_background(
                 self.get_style_context(), ctx,
-                allocation.x, allocation.y,
-                allocation.width, allocation.height)
+                0, 0, allocation.width, allocation.height)
+            scale = self.device_pixel_ratio
+            # Scale physical drawing to logical size.
+            ctx.scale(1 / scale, 1 / scale)
+            self._renderer.set_context(ctx)
+            # Set renderer to physical size so it renders in full resolution.
+            self._renderer.width = allocation.width * scale
+            self._renderer.height = allocation.height * scale
             self._renderer.dpi = self.figure.dpi
             self.figure.draw(self._renderer)
 
