Yes you’re almost there. I did a quick test to make sure it’s working as I thought, this is the end result:
The important thing is that the stencil value is for the entire mesh unfortunately, so the mesh that needs to be cut has to be rendered twice:
- One with the original normal orientation, and a stencil value of 0
- One with inverted normals (to render the interior faces) with a stencil value of 1
Now you should be able to identify the pixels that belong to the interior faces and that are not covered by any exterior faces:
The material for these 2 meshes is the same, and has nothing special beside the box mask as you did.
The material for the “cutter box” is fairly simple too:
Hope that helps!