Rendering Lines

This Odforce post, particulary the file provided by MENOZ, describes how to render additive lines in Houdini with a falloff on the edges.

An important note, when you set Surface Opacity (Of) to 0 in the shader, you have to disable stochastic transparency in the Mantra node. If you need to keep that enabled, you can set Of to a very low constant and get a similar result.

Also, the modern uvcoords node uses u and v instead of s and t like the example file. u is the component you want for falloff on the edges.

TODO: Add example Houdini file

Render State VOP

Sometimes you need to access render time attributes within a shader. The main usecase for this is accessing primitive attributes on packed primitives. Lay down a renderstate node, and add packed:your_attribute to the value name. The dropdown has a bunch of useful options as well.

Cryptomatte Pieces

Lewis Saunders has a great overview of how to apply cryptomatte to pieces inside a geo node in Mantra.

In short:

  • Add vm_gifile render property to your material
  • Where you assign your material add a local override. Enable Overrides use local variables and select vm_gifile from the Choose Parameter dropdown. Put $NAME or another unique primitive attribute as the string.
  • Add a Cryptomatte layer to the Mantra ROP and set the property to gifile