Skinned Mesh Shader Optimizations and C++ changes to support

[naitro2010]

Description

This PR moves some processing that used to run on the GPU for every skinned vertex into a precomputed step on the CPU to hopefully improve frame rates with lots of visible avatars.

Here is the linked issue: #6255

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Checklist

Please ensure the following before requesting review:

• [Y] I have provided a clear title and detailed description for this pull request.
• [Y] If useful, I have included media such as screenshots and video to show off my changes.
• [Y] The PR is linked to a relevant issue with sufficient context.
• [M] I have tested the changes locally and verified they work as intended. (I cherrypicked the changes from a local branch with my other modifications to Alchemy Viewer. They work on Alchemy Viewer with my local build.)
• [?] All new and existing tests pass.
• [?] Code follows the project's style guidelines.
• [?] Documentation has been updated if needed.
• [Y] Any dependent changes have been merged and published in downstream modules
• [Y] I have reviewed the contributing guidelines.

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Additional Notes

This is my first time creating a pull request for Second Life.
Please let me know if I can do anything to improve the next pull requests I make or if there are any code quality issues that I can fix.
I mostly wrote these changes to improve the frame rate for my new version of the viewer with Stereo 3D Virtual Reality rendering that I've been working on but I think they might help with normal rendering too.
I don't have a large number of different GPUs to test on so I'm leaving this pull request as a draft until more people are able to test it on their hardware.

[github-actions]

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[naitro2010]

I have read the CLA Document and I hereby sign the CLA

[naitro2010]

Is there a way to make a release build for this pull request with GitHub actions that I can download and test? I've only tested with a local build so far.

Thanks :)

[akleshchev]

Is there a way to make a release build for this pull request with GitHub actions that I can download and test?

There is a full, downloadable build at the bottom?

[naitro2010]

I just merged the latest changes from develop because the newer LLSD parsing integration test failed to pass.

[naitro2010]

Apparently GitHub is having internal server errors when downloading dependencies now 😢

[akleshchev]

@naitro2010 there is a green checkbox near the commit, click it, it will show a list of 'checks', that's the build, open any OS specifc one and go to summary.

Artifacts are at the bottom of the summary. https://github.com/secondlife/viewer/actions/runs/34837962086

[naitro2010]

@akleshchev Thanks :)

I'll test with the release build on Windows now.

[akleshchev]

Note that it's ReleaseOS, not Release, but the difference should be negligible for shaders.

[naitro2010]

I just tested and it seems like avatar and skinned mesh rendering works on Windows without any issues.
I'm not sure how to profile for A/B testing though.
I think I did see a way to record and replay a connection in the Advanced or Developer menu but I'm not sure how to use it or if it will work for profiling the same scene multiple times.

[akleshchev]

Basically you moved some repeating math from gpu to make it one-time on cpu?

Sadly shaders are not in my wheelhouse and I have no idea how to test skinning either.