FIX: add check if the renderer exists

tacaswell · tacaswell · commit 83150d779818 · 2015-09-13T17:17:09.000-04:00
There exists a path where paintEvent can be called before the first time
that `draw` has been called.  This results in an exception because the
call to `FigureCanvasAgg.draw(self)` is what create the renderer
attribute on the canvas.
diff --git a/lib/matplotlib/backends/backend_qt5agg.py b/lib/matplotlib/backends/backend_qt5agg.py
@@ -75,7 +75,13 @@ def paintEvent(self, e):
         In Qt, all drawing should be done inside of here when a widget is
         shown onscreen.
         """
-        # FigureCanvasQT.paintEvent(self, e)
+        # if the canvas does not have a renderer, then
+        # FigureCanvasAgg.draw(self)  has never been called so force it to
+        # be called to create the renderer and to render the initial view
+        # of the figure
+        if not hasattr(self, 'renderer'):
+            FigureCanvasAgg.draw(self)
+
         if DEBUG:
             print('FigureCanvasQtAgg.paintEvent: ', self,
                   self.get_width_height())
