Avoid double draw in qt5cairo.

anntzer · anntzer · commit fd8e190804e6 · 2018-02-08T17:53:13.000+01:00
diff --git a/lib/matplotlib/backends/backend_qt5cairo.py b/lib/matplotlib/backends/backend_qt5cairo.py
@@ -7,22 +7,30 @@ class FigureCanvasQTCairo(FigureCanvasQT, FigureCanvasCairo):
     def __init__(self, figure):
         super(FigureCanvasQTCairo, self).__init__(figure=figure)
         self._renderer = RendererCairo(self.figure.dpi)
+        self._renderer.set_width_height(-1, -1)  # Invalid values.
+
+    def draw(self):
+        if hasattr(self._renderer.gc, "ctx"):
+            self.figure.draw(self._renderer)
+        super(FigureCanvasQTCairo, self).draw()
 
     def paintEvent(self, event):
         self._update_dpi()
         dpi_ratio = self._dpi_ratio
         width = dpi_ratio * self.width()
         height = dpi_ratio * self.height()
-        surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height)
-        self._renderer.set_ctx_from_surface(surface)
-        self._renderer.set_width_height(width, height)
-        self.figure.draw(self._renderer)
-        buf = surface.get_data()
+        if (width, height) != self._renderer.get_canvas_width_height():
+            surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height)
+            self._renderer.set_ctx_from_surface(surface)
+            self._renderer.set_width_height(width, height)
+            self.figure.draw(self._renderer)
+        buf = self._renderer.gc.ctx.get_target().get_data()
         qimage = QtGui.QImage(buf, width, height,
                               QtGui.QImage.Format_ARGB32_Premultiplied)
         # Adjust the buf reference count to work around a memory leak bug in
         # QImage under PySide on Python 3.
         if QT_API == 'PySide' and six.PY3:
+            import ctypes
             ctypes.c_long.from_address(id(buf)).value = 1
         if hasattr(qimage, 'setDevicePixelRatio'):
             # Not available on Qt4 or some older Qt5.
