UsdImagingDelegate::PopulateSelection() adds too many instances to HdSelection

[williamkrick]

Description of Issue

A call to UsdImagingDelegate::PopulateSelection for a USDXform prim which is a parent to an instancer with N instances (that uses UsdImagingInstanceAdapter) will create an HdSelection which contains N^2 instances.

Steps to Reproduce

1. Create a scene with a USDXform that is a parent to an instancer. The instancer should have N instances. In my case it has 11.
2. Using for favorite USD app, call UsdImagingDelegate::PopulateSelection() on the USDXform that is the parent (or higher ancestor) or the instancer. The instanceIndex parameter should be UsdImagingDelegate::ALL_INSTANCES.
3. Examine the resulting HdSelection for the instancer. Inside instanceIndices I find N^2 indices (121 rather than 11).

I noticed this when working on MayaUSD issue Autodesk/maya-usd#575. ProxyRenderDelegate::_FilterSelection() makes the call to PopulateSelection as I have described above, and we look at the resulting selection state at https://github.com/Autodesk/maya-usd/blob/dev/lib/mayaUsd/render/vp2RenderDelegate/mesh.cpp#L1295.

What seems to be happening is the call to _GatherDependencies in PopulateSelection finds a path to all N instances. Then each call to PopulateSelection is on an UsdImagingInstanceAdapter. That gets the UsdImagingDelegate::ALL_INSTANCES parameter and adds N instances. The adding N instances happens N times, so N^2 instanceIndices.

hd.dll!pxrInternal_v0_20__pxrReserved__::HdSelection::AddInstance(const pxrInternal_v0_20__pxrReserved__::HdSelection::HighlightMode & mode, const pxrInternal_v0_20__pxrReserved__::SdfPath & path, const pxrInternal_v0_20__pxrReserved__::VtArray<int> & instanceIndices) Line 48 (c:\dev\ecg-usd-build\ecg-usd-build\usd\pxr\imaging\hd\selection.cpp:48)
usdImaging.dll!pxrInternal_v0_20__pxrReserved__::UsdImagingPrimAdapter::PopulateSelection(const pxrInternal_v0_20__pxrReserved__::HdSelection::HighlightMode & mode, const pxrInternal_v0_20__pxrReserved__::SdfPath & cachePath, const pxrInternal_v0_20__pxrReserved__::UsdPrim & usdPrim, const int hydraInstanceIndex, const pxrInternal_v0_20__pxrReserved__::VtArray<int> & parentInstanceIndices, const std::shared_ptr<pxrInternal_v0_20__pxrReserved__::HdSelection> & result) Line 420 (c:\dev\ecg-usd-build\ecg-usd-build\usd\pxr\usdImaging\usdImaging\primAdapter.cpp:420)
usdImaging.dll!pxrInternal_v0_20__pxrReserved__::UsdImagingInstanceAdapter::_PopulateInstanceSelectionFn::operator()(const std::vector<pxrInternal_v0_20__pxrReserved__::UsdPrim,std::allocator<pxrInternal_v0_20__pxrReserved__::UsdPrim> > & instanceContext, unsigned __int64 instanceIdx) Line 2204 (c:\dev\ecg-usd-build\ecg-usd-build\usd\pxr\usdImaging\usdImaging\instanceAdapter.cpp:2204)
usdImaging.dll!pxrInternal_v0_20__pxrReserved__::UsdImagingInstanceAdapter::_RunForAllInstancesToDrawImpl<pxrInternal_v0_20__pxrReserved__::UsdImagingInstanceAdapter::_PopulateInstanceSelectionFn>(const pxrInternal_v0_20__pxrReserved__::UsdPrim & instancer, std::vector<pxrInternal_v0_20__pxrReserved__::UsdPrim,std::allocator<pxrInternal_v0_20__pxrReserved__::UsdPrim> > * instanceContext, unsigned __int64 * instanceIdx, pxrInternal_v0_20__pxrReserved__::UsdImagingInstanceAdapter::_PopulateInstanceSelectionFn * fn) Line 591 (c:\dev\ecg-usd-build\ecg-usd-build\usd\pxr\usdImaging\usdImaging\instanceAdapter.cpp:591)
usdImaging.dll!pxrInternal_v0_20__pxrReserved__::UsdImagingInstanceAdapter::_RunForAllInstancesToDraw<pxrInternal_v0_20__pxrReserved__::UsdImagingInstanceAdapter::_PopulateInstanceSelectionFn>(const pxrInternal_v0_20__pxrReserved__::UsdPrim & instancer, pxrInternal_v0_20__pxrReserved__::UsdImagingInstanceAdapter::_PopulateInstanceSelectionFn * fn) Line 556 (c:\dev\ecg-usd-build\ecg-usd-build\usd\pxr\usdImaging\usdImaging\instanceAdapter.cpp:556)
usdImaging.dll!pxrInternal_v0_20__pxrReserved__::UsdImagingInstanceAdapter::PopulateSelection(const pxrInternal_v0_20__pxrReserved__::HdSelection::HighlightMode & highlightMode, const pxrInternal_v0_20__pxrReserved__::SdfPath & cachePath, const pxrInternal_v0_20__pxrReserved__::UsdPrim & usdPrim, const int hydraInstanceIndex, const pxrInternal_v0_20__pxrReserved__::VtArray<int> & parentInstanceIndices, const std::shared_ptr<pxrInternal_v0_20__pxrReserved__::HdSelection> & result) Line 2354 (c:\dev\ecg-usd-build\ecg-usd-build\usd\pxr\usdImaging\usdImaging\instanceAdapter.cpp:2354)
usdImaging.dll!pxrInternal_v0_20__pxrReserved__::UsdImagingDelegate::PopulateSelection(const pxrInternal_v0_20__pxrReserved__::HdSelection::HighlightMode & highlightMode, const pxrInternal_v0_20__pxrReserved__::SdfPath & usdPath, int instanceIndex, const std::shared_ptr<pxrInternal_v0_20__pxrReserved__::HdSelection> & result) Line 2088 (c:\dev\ecg-usd-build\ecg-usd-build\usd\pxr\usdImaging\usdImaging\delegate.cpp:2088)
mayaUsd.dll!pxrInternal_v0_20__pxrReserved__::ProxyRenderDelegate::_FilterSelection() Line 717 (c:\dev\usd\ecg-maya-usd\maya-usd\lib\mayaUsd\render\vp2RenderDelegate

I would expect instanceIndices to contain each index only once. I would also expect the HdSelectionState to have fullySelected=true, but I don't get that either.

Maybe we are making the call to PopulateSelection incorrectly? Or maybe I am interpreting the instanceIndices buffer incorrectly? Any additional information would be helpful.

System Information (OS, Hardware)

Windows

Package Versions

USD v20.05, MayaUSD dev branch at 2164db46

Build Flags

[williamkrick]

I just re-tested this in dev @ commit e7ff8e8 and I can't reproduce it there, so closing.