Hi.

Which is the easiest way to render out mask based on geometry or material?

Thanks you all

You can generate Object ID pass based on their material. Tomas has a sample HIP file over at ODFORCE: http://forums.odforce.net/topic/16070-object-mask-passes/?tab=comments#comment-106311 [forums.odforce.net]

There are many ways to do it in Houdini (and I got spoiled with the MultiMatteElement pass in Vray which is very easy and quick to setup!) like:

1. Setting up geo node with object merge for the objects that you wanted to apply a constant shader.
   
2. Create as many mantra nodes with their own unique force objects and force matte list.
   
3. In special cases, factoring in if the object mask will be refracted/reflected and identifying which shader that requires the diffuse map/colour to be disabled for proper refracted/reflected mask render.