Qt dpi handling should be renderer-agnostic.

matplotlib · anntzer · Jun 15, 2017 · Jun 18, 2017 · Jun 18, 2017 · Jun 18, 2017
commit 5087c055fea96dead4ab1c6c8e647def16828fbb
diff --git a/lib/matplotlib/backends/backend_qt5.py b/lib/matplotlib/backends/backend_qt5.py
@@ -270,6 +270,26 @@ def _dpi_ratio(self):
         except AttributeError:
             return 1
 
+    def _update_dpi(self):
+        # As described in __init__ above, we need to be careful in cases with
+        # mixed resolution displays if dpi_ratio is changing between painting
+        # events.
+        # Return whether we triggered a resizeEvent (and thus a paintEvent)
+        # from within this function.
+        if self._dpi_ratio != self._dpi_ratio_prev:
+            # We need to update the figure DPI.
+            self._update_figure_dpi()
+            self._dpi_ratio_prev = self._dpi_ratio
+            # The easiest way to resize the canvas is to emit a resizeEvent
+            # since we implement all the logic for resizing the canvas for
+            # that event.
+            event = QtGui.QResizeEvent(self.size(), self.size())
+            self.resizeEvent(event)
+            # resizeEvent triggers a paintEvent itself, so we exit this one
+            # (after making sure that the event is immediately handled).
+            return True
+        return False
+
     def get_width_height(self):
         w, h = FigureCanvasBase.get_width_height(self)
         return int(w / self._dpi_ratio), int(h / self._dpi_ratio)
@@ -489,6 +509,7 @@ def draw_idle(self):
     def _draw_idle(self):
         if self.height() < 0 or self.width() < 0:
             self._draw_pending = False
+        if not self._draw_pending:
             return
         try:
             self.draw()

diff --git a/lib/matplotlib/backends/backend_qt5agg.py b/lib/matplotlib/backends/backend_qt5agg.py
@@ -35,30 +35,13 @@ def paintEvent(self, e):
         In Qt, all drawing should be done inside of here when a widget is
         shown onscreen.
         """
-        # if there is a pending draw, run it now as we need the updated render
-        # to paint the widget
-        if self._agg_draw_pending:
-            self.__draw_idle_agg()
-        # As described in __init__ above, we need to be careful in cases with
-        # mixed resolution displays if dpi_ratio is changing between painting
-        # events.
-        if self._dpi_ratio != self._dpi_ratio_prev:
-            # We need to update the figure DPI
-            self._update_figure_dpi()
-            self._dpi_ratio_prev = self._dpi_ratio
-            # The easiest way to resize the canvas is to emit a resizeEvent
-            # since we implement all the logic for resizing the canvas for
-            # that event.
-            event = QtGui.QResizeEvent(self.size(), self.size())
-            # We use self.resizeEvent here instead of QApplication.postEvent
-            # since the latter doesn't guarantee that the event will be emitted
-            # straight away, and this causes visual delays in the changes.
-            self.resizeEvent(event)
-            # resizeEvent triggers a paintEvent itself, so we exit this one.
+        if self._update_dpi():
+            # The dpi update triggered its own paintEvent.
             return
+        self._draw_idle()  # Only does something if a draw is pending.
 
-        # if the canvas does not have a renderer, then give up and wait for
-        # FigureCanvasAgg.draw(self) to be called
+        # If the canvas does not have a renderer, then give up and wait for
+        # FigureCanvasAgg.draw(self) to be called.
         if not hasattr(self, 'renderer'):
             return
 

diff --git a/lib/matplotlib/backends/backend_qt5cairo.py b/lib/matplotlib/backends/backend_qt5cairo.py
@@ -9,6 +9,7 @@ def __init__(self, figure):
         self._renderer = backend_cairo.RendererCairo(self.figure.dpi)
 
     def paintEvent(self, event):
+        self._update_dpi()
         width = self.width()
         height = self.height()
         surface = backend_cairo.cairo.ImageSurface(