matplotlib/matplotlib — pull request #2449 by tacaswell (2013-09-22 15:40:13+00:00)
Title: Qt4 clear before draw

Clears the canvas before re-drawing the QtAgg canvas. This matters if you have an updating figure with a transparent patch (http://stackoverflow.com/questions/18944561/matplotlib-pyqt4-transparent-figure).

I think this is a bug fix, but this will rebase cleanly to master if people disagree.