Dear developers, I discovered that in backend_wx.py in _onPaint(), the callback function for repainting a matplotlib figure, every time a repaint is done also the bitmap is rerendered: backend_wx.py/_onPaint(): ... # Render to the bitmap self.draw(repaint=False) ... This also affects the behaviour of the wxagg backend. Rerendering and therefore also repainting gets quite slow if, e.g., images are included in the figure. I can see this by simply dragging another window across the matplotlibfigure. Commenting out the rerendering I get a much smoother behaviour. I could not observe problems except that sometimes some parts of the figure are not properly repainted if the matplotlib figure is in the background (I only tested the wxagg backend). Therefore it seems that this rerendering every time a repaint is performed is not really necessary and should be avoided. I tested this on matplotlib 0.91.2 on WinXP, Python 2.5, wx 2.8.7. I checked that in the current svn version the _onPaint() function is unchanged. Gregor