The educational resources for combining Pd/GEM with GLSL are indeed quite limited.

I also found the BangYourHead repository which gives some nice examples for standalone GLSL use, but if you want to know how to combine pix-objects with glsl you are a bit lost.

For my current research (trying to combine [pix_freenect] with glsl) I found this patch quite useful: https://github.com/kronihias/pd-kinect-examples/blob/master/02-background-subtraction/02-01-background-subtraction-opengl-shader.pd

(although I don't fully understand where the DepthMap uniform variable is coming from)

What is your "glsl video effect patch" that you refer to?