Use correct DPI when drawing in Cairo renderers

Unlike the Agg renderer, the Cairo renderer exists forever and is at the
DPI when the figure was created. This needs to be updated before drawing
or things in physical sizes (e.g., text or line widths) will be the
wrong size.

Author: QuLogic

lib/matplotlib/backends/backend_gtk3cairo.py

@@ -28,6 +28,7 @@ def on_draw_event(self, widget, ctx):
                 allocation.width, allocation.height)
             self._renderer.set_width_height(
                 allocation.width, allocation.height)
+            self._renderer.dpi = self.figure.dpi
             self.figure.draw(self._renderer)
 
 

lib/matplotlib/backends/backend_gtk4cairo.py

@@ -27,6 +27,7 @@ def on_draw_event(self, widget, ctx):
                 allocation.width, allocation.height)
             self._renderer.set_width_height(
                 allocation.width, allocation.height)
+            self._renderer.dpi = self.figure.dpi
             self.figure.draw(self._renderer)
 
 

lib/matplotlib/backends/backend_qtcairo.py

@@ -13,6 +13,7 @@ def __init__(self, figure=None):
 
     def draw(self):
         if hasattr(self._renderer.gc, "ctx"):
+            self._renderer.dpi = self.figure.dpi
             self.figure.draw(self._renderer)
         super().draw()
 
@@ -23,6 +24,7 @@ def paintEvent(self, event):
             surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height)
             self._renderer.set_ctx_from_surface(surface)
             self._renderer.set_width_height(width, height)
+            self._renderer.dpi = self.figure.dpi
             self.figure.draw(self._renderer)
         buf = self._renderer.gc.ctx.get_target().get_data()
         if QT_API == "PyQt6":

lib/matplotlib/backends/backend_tkcairo.py

@@ -18,6 +18,7 @@ def draw(self):
         surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height)
         self._renderer.set_ctx_from_surface(surface)
         self._renderer.set_width_height(width, height)
+        self._renderer.dpi = self.figure.dpi
         self.figure.draw(self._renderer)
         buf = np.reshape(surface.get_data(), (height, width, 4))
         _backend_tk.blit(

lib/matplotlib/backends/backend_wxcairo.py

@@ -35,6 +35,7 @@ def draw(self, drawDC=None):
         surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height)
         self._renderer.set_ctx_from_surface(surface)
         self._renderer.set_width_height(width, height)
+        self._renderer.dpi = self.figure.dpi
         self.figure.draw(self._renderer)
         self.bitmap = wxcairo.BitmapFromImageSurface(surface)
         self._isDrawn = True