Exercise: Asset Parameterization#

In this exercise, you’ll create a primvar as an asset parameter to control the accent color of the building’s awning. Note that we have updated the lrg_bldgF asset so that the roof material now accepts a primvar for its diffuseColor.

  1. In Visual Studio Code, open the following file: asset_structure/exercise_05/contents/shading.usd

  2. Then, find the following snippet in the file (it should be around line 86).

86def Shader "PrimvarAccentColor"
87{
88    uniform token info:id = "UsdPrimvarReader_float3"
89    float3 inputs:fallback = (0.3372549, 0.7372549, 0.6)
90    string inputs:varname = "accentColor"
91    float3 outputs:result
92}

This material graph now uses a UsdPrimvarReader_float3 to read a primvar called primvars:accentColor with a fallback color if it does not find a primvar. The inputs:fallback is the green color we saw previously for the roof.

Let’s explore what happens when we author primvars:accentColor.

  1. In Visual Studio Code, open the following file: asset_structure/exercise_05/create_asset_parameters.py

1stage: Usd.Stage = Usd.Stage.Open(str(working_dir / "lrg_bldgF.usd"))
2default_prim: Usd.Prim = stage.GetDefaultPrim()
3primvars_api = UsdGeom.PrimvarsAPI(default_prim)
4accent_color = primvars_api.CreatePrimvar("accentColor", Sdf.ValueTypeNames.Float3, UsdGeom.Tokens.constant)
5accent_color.Set((1.0, 0.0, 0.0))

In the code, we are creating the primvar using the PrimvarsAPI and setting the color to red.

  1. In the terminal, run the following command to execute the script:

Windows:

python .\asset_structure\exercise_05\create_asset_parameters.py

Linux:

python ./asset_structure/exercise_05/create_asset_parameters.py

  1. Run the following command in the terminal to view the file in usdview:

Windows:

.\scripts\usdview.bat .\asset_structure\exercise_05\lrg_bldgF.usd

Linux:

./scripts/usdview.sh ./asset_structure/exercise_05/lrg_bldgF.usd

At first glance, we can see that the roof is now red. When selecting the roof prim in the tree view, then selecting the accentColor in the Property panel, we can observe in the Meta Data panel that this accent color is being inherited down the prim hierarchy from the asset parameter we created, rather than from the UsdPrimvarReader’s fallback value. The (i) symbol next to the attribute name indicates that it is an “inherited property.”