Yes Mark, this the first patch join to this mail (paintandvideo.pd).
Single buffered drawing won't work with what he is describing, unless he repaints all of the brush strokes. When a new video frame is drawn, it will overwrite everything. This can be worked around by playing with the Z values though...set the video to draw behind the brush strokes and then make sure that you do Z writes for the brushes. However, you won't be able to do alpha with this...
A dynamic system (heavy) in the second patch (paintandvideobuf0.pd) with 2 abstraction mycircle and my curve. I will try with texture next time.
The best way to do this would be to either cache the brushes or renderer the brushes to another render target with alpha. Then draw the video frame and draw the brush over top. You could also hand render the brushes to a texture with alpha and then just draw the quad. I don't know what the current set of GEM objects is though, so these 2 ideas might require creating some new objects.