Attempt to fix an issue with the MergingSceneIndex. #3263
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When triggering a "whole scene" removal, this scene index can cause the whole scene to be "added", and nothing to be "removed", which is a problem. This can be triggered by the removeal of a sublayer from the stage. This way of handling the change causes accesses to expired UsdPrims, which throw exceptions. This commit attempts to be more precise about the add and remove changes sent in this situation by "adding" prims that are still in any merged scene index, and "removing" any prims that exist only in the scene index that triggered the change. This can result in a _lot_ of small changes instead of one big change, so there may be a need to optimize this, but I think the principle is correct (and the commit does prevent the invlid UsdPrim access exceptions).
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Filed as internal issue #USD-10054 |
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Description of Change(s)
When triggering a "whole scene" removal, this scene index can cause the whole scene to be "added", and nothing to be "removed", which is a problem. This can be triggered by the removeal of a sublayer from the stage. This way of handling the change causes accesses to expired UsdPrims, which throw exceptions.
This commit attempts to be more precise about the add and remove changes sent in this situation by "adding" prims that are still in any merged scene index, and "removing" any prims that exist only in the scene index that triggered the change. This can result in a lot of small changes instead of one big change, so there may be a need to optimize this, but I think the principle is correct (and the commit does prevent the invlid UsdPrim access exceptions).
I'm not at all sure that this is the right fix here, but it was enough to get me over the bump I hit with using USDIMAGINGGL_ENGINE_ENABLE_SCENE_INDEX=1 in Houdini (which does a lot of sublayer removal and adding on a hydra-watched stage). So this is really more meant as a starting point rather than something I expect to be merged as is.
Fixes Issue(s)
3261
[ X ] I have verified that all unit tests pass with the proposed changes
[ X ] I have submitted a signed Contributor License Agreement