[PD] render into rectangle

[marius schebella]

Hi,
I need to project a certain rectangle/quadrangle with a videobeamer. It is a 
distorted and non 4:3 area. I wonder if it possible to render the gembuffer 
into such a polygon. The rest of the screen should remain black. So I know 
how to render images and videos into that area, but I didn't find an easy 
solution to texture/snap the whole gemwindow into that rectangle. I would 
like to have some particle effects. the only way I can think of is using 
single buffer mode and pix_snap a buffer, then clear it and then texture 
onto my polygon. Do you have other ideas?
thank you. marius.