Filtering Shadows


I just want to filter my shadow volumes and think about the best way.

So I get my stencil buffer with glReadPixels and run a filter ( box/gaussian )on it and then draw it on screen with glDrawPixel.
But glConvolution is slow, so I got Intel’s Image Processing Lib which is faster.
I also thought about using hardware- bi-linear filtering, but this was slow, maybe because I need a gluScaleImage call to scale the stencil image e.g. from 640x480 to 512x512…

Thanks for any suggestions or tips