// ------------------------------------------------------------------------------------------ //
// Helper functions.
// ------------------------------------------------------------------------------------------ //
/// <summary>
/// Reads the material associated with the geometry at the target path. If a valid material is
/// bound, the "surface" shader is inspected, if valid, the shader ID is queried and returned
/// via the shaderId output parameter. Returns true when shaderId is set.
/// </summary>
static public bool ReadMaterial(Scene scene,
string geometryPath,
MaterialSample materialSample,
out string shaderId)
{
// Discover the material bound to the geometry.
// Note that with this structure, the geometry type does not matter.
var geomMaterialBinding = new MaterialBindingSample();
// Discover the binding for the geometry.
// Note that the details of how to import geometry is handled in a different example.
scene.Read(geometryPath, geomMaterialBinding);
// In general, there is no guarantee that any prim is bound, so this null check is always
// required.
if (geomMaterialBinding.binding.targetPaths == null)
{
// In this example, exceptions are thrown on invalid data, but in practice invalid bindings
// should probably be collected into a summary report and emitted as a single warning.
throw new System.Exception("Expected bound material");
}
// Similarly, there is no guarantee the source file is well formed, so an invalid number of
// target paths must also be handled.
if (geomMaterialBinding.binding.targetPaths.Length != 1)
{
throw new System.Exception("Expected exactly one target path for material binding");
}
// Read the material, which will provide the shader binding.
scene.Read(geomMaterialBinding.binding.targetPaths[0], materialSample);
// Again, the surface may be invalid, so protect against broken scene description.
if (materialSample.surface == null || string.IsNullOrEmpty(materialSample.surface.connectedPath))
{
throw new System.Exception("Material had no surface bound");
}
string shaderPath = materialSample.surface.connectedPath.Replace(".outputs:out", "");
var prim = scene.Stage.GetPrimAtPath(new pxr.SdfPath(shaderPath));
if (prim == null || !prim.IsValid())
{
throw new System.Exception("Invalid shader prim");
}
var val = new VtValue();
if (!prim.GetAttributeValue(new TfToken("info:id"), val, scene.Time ?? UsdTimeCode.Default()))
{
throw new System.Exception("Shader prim had no identifier");
}
shaderId = pxr.UsdCs.VtValueToTfToken(val).ToString();
return(true);
}