how is it possible to mask an image with geos e.g. [slideSquares]? with pix_mask it doesn't seem to work, i guess because the [slideSquares] ain't no pix data or whatever...
is this possible? do i have to convert the geos somehow?

okay, i found this thread:
http://puredata.hurleur.com/sujet-868-help-masking-goes-wih-other-geos-gem
i got it working with this, but the point is, i have no clue what is going on there. is there somwhere out there in the web a good tutorial for GEM using this openGL stuff?
the examples in the help browser are decorated very meager with helpful comments.