matplotlib · anntzer · Sep 26, 2017 · Sep 18, 2017 · Sep 22, 2017 · Sep 22, 2017
diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -1845,6 +1845,7 @@ def resize_event(self):
         s = 'resize_event'
         event = ResizeEvent(s, self)
         self.callbacks.process(s, event)
+        self.draw_idle()
 
     def close_event(self, guiEvent=None):
         """Pass a `CloseEvent` to all functions connected to ``close_event``.

diff --git a/lib/matplotlib/backends/backend_qt5.py b/lib/matplotlib/backends/backend_qt5.py
@@ -359,9 +359,10 @@ def resizeEvent(self, event):
         winch = w / dpival
         hinch = h / dpival
         self.figure.set_size_inches(winch, hinch, forward=False)
-        FigureCanvasBase.resize_event(self)
-        self.draw_idle()
+        # pass back into Qt to let it finish
         QtWidgets.QWidget.resizeEvent(self, event)
+        # emit our resize events
+        FigureCanvasBase.resize_event(self)
 
     def sizeHint(self):
         w, h = self.get_width_height()

diff --git a/lib/matplotlib/backends/backend_qt5agg.py b/lib/matplotlib/backends/backend_qt5agg.py
@@ -56,7 +56,10 @@ 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.
@@ -72,7 +75,6 @@ def paintEvent(self, e):
             # 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)
-            QtWidgets.QApplication.instance().processEvents()
             # resizeEvent triggers a paintEvent itself, so we exit this one.
             return
 
@@ -138,6 +140,8 @@ def draw_idle(self):
             QtCore.QTimer.singleShot(0, self.__draw_idle_agg)
 
     def __draw_idle_agg(self, *args):
+        if not self._agg_draw_pending:
+            return
         if self.height() < 0 or self.width() < 0:
             self._agg_draw_pending = False
             return

diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
@@ -708,14 +708,14 @@ def set_size_inches(self, w, h=None, forward=True):
 
         Usage ::
 
-             fig.set_size_inches(w,h)  # OR
-             fig.set_size_inches((w,h))
+             fig.set_size_inches(w, h)  # OR
+             fig.set_size_inches((w, h))
 
         optional kwarg *forward=True* will cause the canvas size to be
         automatically updated; e.g., you can resize the figure window
         from the shell
 
-        ACCEPTS: a w,h tuple with w,h in inches
+        ACCEPTS: a w, h tuple with w, h in inches
 
         See Also
         --------

diff --git a/lib/matplotlib/tests/test_backend_qt5.py b/lib/matplotlib/tests/test_backend_qt5.py
@@ -145,6 +145,11 @@ def test_dpi_ratio_change():
 
         qt_canvas.draw()
         qApp.processEvents()
+        # this second processEvents is required to fully run the draw.
+        # On `update` we notice the DPI has changed and trigger a
+        # resize event to refresh, the second processEvents is
+        # required to process that and fully update the window sizes.
+        qApp.processEvents()
 
         # The DPI and the renderer width/height change
         assert fig.dpi == 240