Is there a way yet to determine the invalid rectangle for a control so you only bother painting that segment?

I know in the past it wasn't possible yet.

I was unable to find a 3D graph that suited my needs so I wrote one. I made it draw at 2X resolution and then stretchblt it down to fit to give it anti-aliasing, but you can really see the speed hit when it blt's the entire image back over.

Thanks,