[Maya-Python] Maya Geometry Shader, with GLSL

[Marcus Ottosson]

Hi all,

I’ve been stuck struggling with this for the past 3 days, and am at the end of my rope. The glslShader plug-in that ships with Maya demonstrates that it does work (see bottom of README), but I can’t get it to work outside of that plug-in.

• https://github.com/mottosso/mayaGeometryShader

What happens?

The pixel shader just seems to stop getting input with a geometry shader in the mix. I’ve tried simply passing data from the vertex to pixel shader via the geometry shader, but for some reason having the geometry shader in the mix completely kills any drawing, without throwing any error.

Why do this?

Ultimately, I’d like to do as much of my plug-in development as possible in Python, and drawing is currently the main culprit when it comes to performance. I’d like to offload some of that burden to GLSL, and draw both geometry and gizmos and visualisations of all kinds by passing tiny amounts of data from Python to OpenGL.

Why not just use the glslShader plug-in?

1. It is highly unoptimised; made for experimenting with shaders rather than actually using it in production on many nodes.
2. It is dynamic; the attributes are dynamically generated based on the contents of the ogsfx file, making scripting towards it that much more tricky.
3. It is a shader, rather than a node; which means each one of my custom nodes need an additional node that go with it. More to manage is bad news.
4. It requires geometry. I’d like to use a geometry shader to draw simple shapes, i.e. plane, box, sphere and capsule, using little to no actual geometry in Maya. This example is almost there, filling the OpenGL buffer directly without the aid from Maya.
5. It doesn’t work in non-textured mode. The drawn geometry is meant to look like any other geo, and should exist in textured and non-textured mode alike.

Hmm.

What could be the cause?

My theory is that there is something I’m not passing along. The glslShader example passes “geometry requirements” and “mutators” into the mix that I’ve yet to fully understand. Another theory is that I also need a “control shader”, and although the TesselationExample does include those, the SilhouetteExample does not and it also works just fine.

Anyone know what’s going on?

Best,
Marcus