Reduce Apple OpenGL vertex state churn

[LisaScheers]

Description

Reduces redundant OpenGL state translation on Apple GPUs by retaining the current vertex/index buffers across shader transitions and caching the vertex attribute pointer formats already valid for the bound buffer.

Only newly required formats are submitted. Color/emissive pointer remapping is preserved, cache state is invalidated on buffer replacement or explicit unbind, and non-Apple drivers retain the existing behavior.

A native Apple Silicon profile of the closely related Firestorm viewer showed repeated time in glVertexAttribPointerARB_Exec, OpenGL object-name hash operations, and dispatch/state updates. The official develop branch has the same unconditional shader-transition unbind and pointer resubmission path.

Related Issues

• Please link to a relevant GitHub issue for additional context.

Issue Link: None; opened as a draft for upstream performance evaluation.

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Checklist

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

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Additional Notes

Validation performed:

• clean git diff --check
• exact stable patch-ID match with the Firestorm implementation
• reviewed cache invalidation and every color/emissive attribute combination
• verified the non-Apple path remains unchanged

A full official viewer build was not available because this host lacks the autobuild dependency bundle and full Xcode toolchain. This remains a draft pending native build and benchmark coverage.

[github-actions]

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[LisaScheers]

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[Copilot]

Pull request overview

This PR reduces redundant OpenGL state work on Apple GPUs by avoiding unconditional vertex/index buffer unbinds on shader transitions and by caching which vertex attribute pointer formats have already been submitted for the currently bound array buffer.

Changes:

• Skip LLVertexBuffer::unbind() during LLGLSLShader::bind() on Apple to retain buffer bindings across shader transitions.
• Add an Apple-only cache in LLVertexBuffer::setupVertexBuffer() to only submit newly needed glVertexAttribPointer* formats, with invalidation on buffer change or explicit unbind.
• Preserve existing color/emissive attribute pointer remapping while avoiding redundant resubmission on Apple.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
indra/llrender/llvertexbuffer.cpp	Adds Apple-only vertex attribute pointer caching and invalidation to reduce redundant glVertexAttribPointer* calls.
indra/llrender/llglslshader.cpp	Avoids unbinding VBO/IBO on shader transitions on Apple to reduce driver translation churn.

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