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[UsdLux] [hdEmbree] Update documentation for UsdLux, and make hdEmbree provide a reference implementation #3200

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@pmolodo pmolodo commented Jul 31, 2024

Description of Change(s)

Everything all in one place!

This PR combines all UsdLux update related PRs - both the documentation updates + hdEmbree reference implementation PRs, for reviewing everything at once.


Related PRs:

Includes these PRs:

⛓️ Just the hdEmbree reference implementaiton PR chain:

📃 Just the documentation PR:
This chain of PRs (implementing UsdLux support in hdEmbree), was made separate from the PR documenting expected UsdLux behavior:

Original PR:
These PRs are an update of this original PR:


But... why??

Why make these PRs in the first place?

The current specifications of the various UsdLux prims + attributes are imprecise or vague in many places, and as a result, actual implementations of them by various renderers have diverged, sometimes quite significantly. For instance, here is Intel's 4004 Moore Lane scene, with the same UsdLux lights defined, in 3 different renderers:

Karma:
4004 Moore Lane, rendered in Karma

Arnold:
4004 Moore Lane, rendered in Arnold

Omniverse RTX:
4004 Moore Lane, rendered in Omniverse RTX

For a full descpription of the problem, see here:

Why so many PRs?
This was my attempt to break up a rather large change into smaller, more easily reviewable changes, that can be merged in incrementally, to help ease the burden for code reviewers.

If you find this confusing, and would rather just one big PR (ie, just this one), or have them organized in some other way, please let me know!

Why are the documentation changes in their own PR?
In some ways, the documentation changes are the heart of this effort - we wish to specify more exactly what the various UsdLux prims and attributes represent. However, building consensus on this may take time - so we expect some dialogue on the exact language or formulas.

Because that may take time, the hdEmbree reference implementation changes are separate, and broken up, so we can hopefully start integrating portions of them even before final consensus has been reached on the final form of the specification.

Why are the documentation changes not broken up into smaller pieces, like the hdEmbree reference implementation changes?
Because I wasn't sure if that would be desireable or not! If people think that would be helpful, I can do so - perhaps breaking out by schema or individual attribute?


  • I have verified that all unit tests pass with the proposed changes
  • I have submitted a signed Contributor License Agreement

pmolodo and others added 6 commits July 29, 2024 23:58
use of std::bind was copying the underlying random number generator before
use, resulting in the exact same sequence getting reused for, ie, every
AO calculation within a given tile-group
- forward-declare some types as struct instead of class (avoids msvc
  compiler warning)
- comment typo fix
Adds more detailed and precise explanations of expected behavior for
UsdLux lights to UsdLux docs.
@pmolodo pmolodo changed the base branch from release to dev July 31, 2024 08:38
@pmolodo pmolodo changed the title Update documentation for UsdLux, and make hdEmbree provide a reference implementation [UsdLux] [hdEmbree] Update documentation for UsdLux, and make hdEmbree provide a reference implementation Jul 31, 2024
anderslanglands and others added 4 commits August 1, 2024 11:44
This modifies the hdEmbree example plugin to do direct lighting so as to
provide a reference implementation of the expected behaviour for UsdLux.

If no lights are present in the stage, the old ambient occlusion path
will be used.
@jesschimein
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Filed as internal issue #USD-9918

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/AzurePipelines run

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Azure Pipelines successfully started running 1 pipeline(s).

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3 participants