> Something pending is the means for drawing only what is really  
> visible. The first I can think of is a 2nd parameter to #drawOn:,  
> consisting of a clipping rectangle.

Or, store it in the canvas. Not sure which way would be better.

> It is usually nil.

Why would it be usually nil? You would certainly want to clip at  
least against the display bounds, wouldn't you? And you might want to  
optionally clip against the parent's bounds.

- Bert -