MNT: ensure no draws are pending in paintEvent

tacaswell · tacaswell · commit ad1534dc15b6 · 2017-09-21T21:52:40.000-04:00
This prevents flickering during window resize.  The issue is that the
resize event triggers a paint and we have marked the figure as stale
and requiring a re-draw.  Sometimes the paint from the resize will
process before the single-shot to trigger __draw_idle_agg and there
will be a size-mismatch between the QImage and the buffer we are
trying to fill it with which results in a visible flicker.
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.
@@ -137,6 +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
