Implicit surfaces sidedness attribute not propagated to the scene index

[cpichard]

Hi,
The "doubleSided" attribute of the implicit geometries (cube, cylinder, sphere, ..) is not propagated to a corresponding hydra prim data source by the UsdImagingSceneIndex scene index. In a way it makes sense as those geometries are closed, and sidedness seems redundant. However when render delegates like Arnold use them with render time CSG operators, or transparent materials, the missing doubleSided parameter affects the ability to properly compute the light interaction with the object. Internally we have several tests failing for this reason when they were working previously with hydra 1.

[tpalmergit15]

Filed as internal issue #USD-11131

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[spitzak]

It makes a pretty huge difference for cameras that are inside the implicit geometry, that might be considered a better reason for fixing this.

[cpichard]

Hi, indeed, scenes with cameras inside an implicit geometry might behave differently.
We have submitted a pull request for fixing this issue: #3689