Hi Juan,

> >> 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.
> >
> Mmmmhhhh. Not sure. Will have to think about this, and perhaps 
> experiment a bit with the alternatives, to see where they lead.

Other alternative is to use the Decorator Pattern. Decorate the original
canvas with a ClippedCanvas that only take care of the clipping area,
and delegates the rest.  The very same can be done with ZoomCanvas,
TranslationCanvas, RotationCanvas, etc.

Cheers,

-- Diego