Qt: Redraw agg buffer in main thread. Implement FigureCanvasQTAggBase…

… init.
6a74cda44d8f467b4d5d2ac25e6ce7ac1efe3852
commit 6a74cda44d8f467b4d5d2ac25e6ce7ac1efe3852
diff --git a/lib/matplotlib/backends/backend_qt4agg.py b/lib/matplotlib/backends/backend_qt4agg.py
@@ -69,6 +69,7 @@ def __init__(self, figure):
         if DEBUG:
             print('FigureCanvasQtAgg: ', figure)
         FigureCanvasQT.__init__(self, figure)
+        FigureCanvasQTAggBase.__init__(self, figure)
         FigureCanvasAgg.__init__(self, figure)
         self._drawRect = None
         self.blitbox = None

diff --git a/lib/matplotlib/backends/backend_qt5.py b/lib/matplotlib/backends/backend_qt5.py
@@ -239,7 +239,6 @@ def __init__(self, figure):
         super(FigureCanvasQT, self).__init__(figure=figure)
         self.figure = figure
         self.setMouseTracking(True)
-        self._idle = True
         w, h = self.get_width_height()
         self.resize(w, h)
 
@@ -415,23 +414,6 @@ def stop_event_loop(self):
 
     stop_event_loop.__doc__ = FigureCanvasBase.stop_event_loop_default.__doc__
 
-    def draw_idle(self):
-        # This cannot be a call to 'update', we need a slightly longer
-        # delay, otherwise mouse releases from zooming, panning, or
-        # lassoing might not finish processing and will not redraw properly.
-        # We use the guard flag to prevent infinite calls to 'draw_idle' which
-        # happens with the 'stale' figure & axes callbacks.
-        d = self._idle
-        self._idle = False
-
-        def idle_draw(*args):
-            try:
-                self.draw()
-            finally:
-                self._idle = True
-        if d:
-            QtCore.QTimer.singleShot(0, idle_draw)
-
 
 class MainWindow(QtWidgets.QMainWindow):
     closing = QtCore.Signal()

diff --git a/lib/matplotlib/backends/backend_qt5agg.py b/lib/matplotlib/backends/backend_qt5agg.py
@@ -58,8 +58,12 @@ class FigureCanvasQTAggBase(object):
 
     Public attribute
 
-      figure - A Figure instance
-   """
+        figure - A Figure instance
+    """
+
+    def __init__(self, figure):
+        super(FigureCanvasQTAggBase, self).__init__(figure=figure)
+        self._agg_draw_pending = False
 
     def drawRectangle(self, rect):
         self._drawRect = rect
@@ -71,10 +75,6 @@ def paintEvent(self, e):
         In Qt, all drawing should be done inside of here when a widget is
         shown onscreen.
         """
-        # If we have not rendered the Agg backend yet, do so now.
-        if not hasattr(self, 'renderer'):
-            FigureCanvasAgg.draw(self)
-
         # FigureCanvasQT.paintEvent(self, e)
         if DEBUG:
             print('FigureCanvasQtAgg.paintEvent: ', self,
@@ -142,15 +142,33 @@ def paintEvent(self, e):
 
     def draw(self):
         """
-        Draw the figure with Agg, and queue a request
-        for a Qt draw.
+        Draw the figure with Agg, and queue a request for a Qt draw.
         """
-        # The Agg draw is done here; delaying it until the paintEvent
-        # causes problems with code that uses the result of the
-        # draw() to update plot elements.
+        # The Agg draw is done here; delaying causes problems with code that
+        # uses the result of the draw() to update plot elements.
         FigureCanvasAgg.draw(self)
         self.update()
 
+    def draw_idle(self):
+        """
+        Queue redraw of the Agg buffer and request Qt paintEvent.
+        """
+        # The Agg draw needs to be handled by the same thread matplotlib
+        # modifies the scene graph from. Post Agg draw request to the
+        # current event loop in order to ensure thread affinity and to
+        # accumulate multiple draw requests from event handling.
+        # TODO: queued signal connection might be safer than singleShot
+        if not self._agg_draw_pending:
+            self._agg_draw_pending = True
+            QtCore.QTimer.singleShot(0, self.__draw_idle_agg)
+
+    def __draw_idle_agg(self, *args):
+        try:
+            FigureCanvasAgg.draw(self)
+            self.update()
+        finally:
+            self._agg_draw_pending = False
+
     def blit(self, bbox=None):
         """
         Blit the region in bbox
@@ -186,8 +204,7 @@ class FigureCanvasQTAgg(FigureCanvasQTAggBase,
     def __init__(self, figure):
         if DEBUG:
             print('FigureCanvasQtAgg: ', figure)
-        FigureCanvasQT.__init__(self, figure)
-        FigureCanvasAgg.__init__(self, figure)
+        super(FigureCanvasQTAgg, self).__init__(figure=figure)
         self._drawRect = None
         self.blitbox = None
         self.setAttribute(QtCore.Qt.WA_OpaquePaintEvent)