Assign materials to GeomSubSets in instances?

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1

Hej,

We are having a lot of rather big meshes with GeomSubSets to apply different materials to sub parts. In our stage we want to have the same mesh many many times but assign different colors to the GeomSubSet for each imported mesh. This works fine if but fails if we use “instanceable = true”.

Is there ANY way to assign materials to GeomSubSet on instanced meshes? We would really like to use instancing to reduce the memory usage of our scenes.

Here is an example that shows the problem we are having. The plane.usda contains a Mesh with two GeomSubSets

#usda 1.0
(
    defaultPrim = "plane"
)

def Xform "plane"
{
def Mesh "mesh"
{
    uniform bool doubleSided = 1
    float3[] extent = [(-0.5, 0, -0.5), (0.5, 0, 0.5)]
    int[] faceVertexCounts = [4, 4]
    int[] faceVertexIndices = [0, 1, 3, 2, 2, 3, 5, 4]
    point3f[] points = [(-0.5, 0, 0.5), (0.5, 0, 0.5), (-0.5, 0, 0), (0.5, 0, 0), (-0.5, 0, -0.5), (0.5, 0, -0.5)]

    def GeomSubset "color_change_1"
    {
        uniform token familyName = "materialBind"
        int[] indices = [0]
    }
    def GeomSubset "color_change_2"
    {
        uniform token familyName = "materialBind"
        int[] indices = [1]
    }
}
}

Then in our main.usda we import it twice, once as normal reference and once instanced and the color change works for the “normal” reference but not for the instanced one

#usda 1.0

def "plane_ref" (
    prepend references = @plane.usda@
    prepend apiSchemas = ["MaterialBindingAPI"]
)
{
    rel material:binding = </mtl/red>
    double3 xformOp:translate = (-1, 0, 0)
    uniform token[] xformOpOrder = ["xformOp:translate"]

    over "mesh" {
        over "color_change_1" {
            rel material:binding = </mtl/blue>
        }
    }
}

def "plane_inst" (
    instanceable = true
    prepend references = @plane.usda@
    prepend apiSchemas = ["MaterialBindingAPI"]
)
{
    rel material:binding = </mtl/red>
    over "mesh" {
        over "color_change_1" {
            rel material:binding = </mtl/blue>
        }
    }
}

def Scope "mtl"
{
    def Material "red"
    {
        token outputs:surface.connect = </mtl/red/red.outputs:surface>
        def Shader "red"
        {
            uniform token info:id = "UsdPreviewSurface"
            color3f inputs:diffuseColor = (1, 0, 0)
            token outputs:surface
        }
    }

    def Material "blue"
    {
        token outputs:surface.connect = </mtl/blue/blue.outputs:surface>
        def Shader "blue"
        {
            uniform token info:id = "UsdPreviewSurface"
            color3f inputs:diffuseColor = (0, 0, 1)
            token outputs:surface
        }
    }
}