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PxrMatteID outputs matte AOVs for compositing.  This requires you add a User Attribute, explained in more detail here.

PxrCryptomatte has since superseded this workflow as a useful and nearly automatic alternative.

Add a user attribute for MatteID0.

Duplicate the fields for:

  • Name
  • Label (this is the UI name)
  • Tags (necessary to see RenderMan attributes and edit them during interactive rendering)
    script_ritype  color
    renderman  attr

Set its type and color value.

Add PxrMatteID

Create a Houdini buildarray node to connect to the Utility Pattern on the PxrSurface material. Then connect a PxrMatteID Pattern node to the buildarray as shown below.

In your PxrMaterialBuilder Network, add a PxrMatteID VOP.  Set the color as the user attribute above.

Connect PxrMatteID's resultAOV to PxrSurface's Utility Pattern.

Set up AOV for Output

Choose the correct/corresponding MatteID AOV output from the RenderMan ROP node Displays Tab

You will notice we set a color on the OBJ with an attribute and there's also a color from the MatteID pattern itself. This is so you can multiply the color of the attribute by the pattern node. For example, you can supply a texture mask to the MatteID pattern node and have it multiplied against the color chosen in the MatteID Attribute