Chris Rydalch

That ordering can't be dynamic; however Houdini 21.0 does offer a new control for Viewport materials. Inside of a Builder node, you can put down the "Houdini Viewport Material Output", and connect it's surface input to a Preview Surface or MaterialX surface shader. This creates an `hview:surface` out, which is the highest priority used by the Viewport when searching for a material. Hopefully this helps!

This is not something vanilla MaterialX materials can really do yet; the Karma Material Builder supports this via the Karma AOV VOP (https://www.sidefx.com/docs/houdini/nodes/vop/kma_aov-2.0.html), which you connect to the builder's output node; Material Library then sets up the Render Var, and the downstream Karma Render Settings should pick that up, and it should show up in the render.

Editing materials to add AOVs isn't super practical right now; hopefully materials-based AOVs will become more standardized/prevalent/supported in MaterialX/UsdMaterialX.

Hope this helps!

Instead of the ramp parm, try the Karma Constant Ramp VOP (https://www.sidefx.com/docs/houdini/nodes/vop/kma_rampconst.html), see if that works for you.