cairo backends do not support blitting; mark them as such.

anntzer · anntzer · commit 38d0b35c0397 · 2017-12-29T10:41:24.000-08:00
Trying to run a blitting animation example on gtk3cairo currently fails
with

    AttributeError: 'FigureCanvasGTK3Cairo' object has no attribute 'copy_from_bbox'

While blitting can be made to work for e.g. qt5cairo, it cannot be for
gtk3cairo which relies on gtk's windowing code to handle us a cairo
context to directly draw on when a draw event occurs: the animation
blitting code fundamentally assumes that it can modify the underlying
buffer whenever it wants and that the windowing system simply displayes
that buffer at each draw event.
diff --git a/lib/matplotlib/backends/backend_cairo.py b/lib/matplotlib/backends/backend_cairo.py
@@ -450,6 +450,8 @@ def set_linewidth(self, w):
 
 
 class FigureCanvasCairo(FigureCanvasBase):
+    supports_blit = False
+
     def print_png(self, fobj, *args, **kwargs):
         width, height = self.get_width_height()
 
