Hydra: Materials bound to geomsubsets are ignored with an "identified" UsdImagingDelegate

[jufrantz]

Description of Issue

When using an UsdImagingDelegate with a delegateID (diff than /), materials bound to geomsubsets are ignored, meshes are rendered with the fallback grey material.

I could reproduce the issue with usdview/Storm thanks to USDIMAGINGGL_ENGINE_DEBUG_SCENE_DELEGATE_ID

Steps to Reproduce

1. Open attached usd scene cube_with_geomsubsets.zip in usdview
2. Notice we have a red and a green material assigned to cube faces, they are correctly rendered in Storm
3. Set USDIMAGINGGL_ENGINE_DEBUG_SCENE_DELEGATE_ID environment variable to any (non root) path, and open the same scene, for instance
   USDIMAGINGGL_ENGINE_DEBUG_SCENE_DELEGATE_ID=/Foo usdview cube_with_geomsubsets.usd
4. Notice that the cube is now rendered without usd material bindings

Note

On our side we are considering patching UsdImagingMeshAdapter::GetTopology this way:

diff --git a/pxr/usdImaging/usdImaging/meshAdapter.cpp b/pxr/usdImaging/usdImaging/meshAdapter.cpp
index f95d0e14a..b1aca9951 100644
--- a/pxr/usdImaging/usdImaging/meshAdapter.cpp
+++ b/pxr/usdImaging/usdImaging/meshAdapter.cpp
@@ -397,7 +397,7 @@ UsdImagingMeshAdapter::GetTopology(UsdPrim const& prim,
                    HdGeomSubset {
                        HdGeomSubset::TypeFaceSet,
                        subset.GetPath(),
-                       GetMaterialUsdPath(subset.GetPrim()),
+                       _ConvertCachePathToIndexPath(_GetMaterialUsdPath(subset.GetPrim())),
                        indices });
             }
         }

Current meshAdapter code assigns an usdPath to HdGeomSubset.materialId, whereas clients in pxr render delegates seem to expect a SPrim path (e.g. HdStGetMaterialNetworkShader() HdPrman_ResolveMaterial())

System Information (OS, Hardware)

• Linux CentOS

Package Versions

• USD-21.11
• USD 22.05a

Build Flags

[sunyab]

Filed as internal issue #USD-7419

[tgvarik]

Shares an underlying cause with #1687

[jufrantz]

Thank you @tgvarik. The fix in USD 22.11 works for us as well; I'm closing the issue.

[jufrantz]

Hello,

I'm reopening the issue as a similar problem has (re)surfaced.
I did notice it with USD-23.08 and didn't test earlier USD versions or 23.11. I will probably give them a try.
It can be reproduced with the same steps as the original issue, using usview and USDIMAGINGGL_ENGINE_DEBUG_SCENE_DELEGATE_ID env.

-- Julien

[jufrantz]

The issue has been found to be on our side within our own USD build.
My apologies for this mix-up.