

How you clear your HTML5 Canvas matters - simonsarris
http://simonsarris.com/blog/346-how-you-clear-your-canvas-matters

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nxn
Ehh, last time I messed with canvas (sometime around February this year) any
approach to clearing the entire canvas was too slow. In order to get any
decent performance I had to layer multiple canvases on top of each other and
keep the dimensions of the last draw operation saved so I'd only have to clear
that bit of the canvas. The layering was so that I wouldn't have to bother
redrawing things like the background after clearing something on top of it.

