I've been playing with GLSL shaders but so far I haven't worked out how to access things like point scale. Are there any samples around somewhere?

You can look at houdini/glsl/particle/GL32/disc.prog (which references the .vert, .frag, and sprite.geom). You basically want:

in your vertex shader to grab pscale. Houdini attributes are matched to GLSL shaders by name.

Very similar question I'm dealing with! This is an old topic but felt like bumping here, an example would be perfect!