Migrate sky/cloud rendering to fragment shader and introduce high precision post process option

[RyeMutt]

Description

Introduces optimizations to sky rendering to reduce vertex shaded overdraw and fix banding introduced as part of the apple silicon optimizations.

This also fixes artifacts in the sky rendering from vertex shading around the sun.

Vertex Shaded with WLSkyDetail of 8

2025-11-26T05:53:52Z INFO # llrender/llglslshader.cpp(191) LLGLSLShader::dumpStats : =============================================
2025-11-26T05:53:52Z INFO # llrender/llglslshader.cpp(192) LLGLSLShader::dumpStats : Deferred Windlight Sky Shader
2025-11-26T05:53:52Z INFO # llrender/llglslshader.cpp(195) LLGLSLShader::dumpStats : deferred/skyV.glsl
2025-11-26T05:53:52Z INFO # llrender/llglslshader.cpp(195) LLGLSLShader::dumpStats : deferred/skyF.glsl
2025-11-26T05:53:52Z INFO # llrender/llglslshader.cpp(198) LLGLSLShader::dumpStats : =============================================
2025-11-26T05:53:52Z INFO # llrender/llglslshader.cpp(215) LLGLSLShader::dumpStats : Triangles Drawn: 351 (0.07 pct of total, 2.880 million/sec)
2025-11-26T05:53:52Z INFO # llrender/llglslshader.cpp(216) LLGLSLShader::dumpStats : Binds: 1 (0.20 pct of total)
2025-11-26T05:53:52Z INFO # llrender/llglslshader.cpp(217) LLGLSLShader::dumpStats : SamplesDrawn: 4999789 (6.63 pct of total, 41.030 billion/sec)
2025-11-26T05:53:52Z INFO # llrender/llglslshader.cpp(218) LLGLSLShader::dumpStats : Time Elapsed: 121856 (5.65 pct of total, 0.12186 ms)

Vertex Shaded with WLSkyDetail of 128

2025-11-26T05:50:57Z INFO # llrender/llglslshader.cpp(191) LLGLSLShader::dumpStats : =============================================
2025-11-26T05:50:57Z INFO # llrender/llglslshader.cpp(192) LLGLSLShader::dumpStats : Deferred Windlight Sky Shader
2025-11-26T05:50:57Z INFO # llrender/llglslshader.cpp(195) LLGLSLShader::dumpStats : deferred/skyV.glsl
2025-11-26T05:50:57Z INFO # llrender/llglslshader.cpp(195) LLGLSLShader::dumpStats : deferred/skyF.glsl
2025-11-26T05:50:57Z INFO # llrender/llglslshader.cpp(198) LLGLSLShader::dumpStats : =============================================
2025-11-26T05:50:57Z INFO # llrender/llglslshader.cpp(215) LLGLSLShader::dumpStats : Triangles Drawn: 21930 (4.22 pct of total, 121.682 million/sec)
2025-11-26T05:50:57Z INFO # llrender/llglslshader.cpp(216) LLGLSLShader::dumpStats : Binds: 1 (0.20 pct of total)
2025-11-26T05:50:57Z INFO # llrender/llglslshader.cpp(217) LLGLSLShader::dumpStats : SamplesDrawn: 4865099 (6.48 pct of total, 26.995 billion/sec)
2025-11-26T05:50:57Z INFO # llrender/llglslshader.cpp(218) LLGLSLShader::dumpStats : Time Elapsed: 180224 (7.94 pct of total, 0.18022 ms)

Pixel Shaded

2025-11-26T05:50:25Z INFO # llrender/llglslshader.cpp(191) LLGLSLShader::dumpStats : =============================================
2025-11-26T05:50:25Z INFO # llrender/llglslshader.cpp(192) LLGLSLShader::dumpStats : Deferred Windlight Sky Shader
2025-11-26T05:50:25Z INFO # llrender/llglslshader.cpp(195) LLGLSLShader::dumpStats : deferred/skyV.glsl
2025-11-26T05:50:25Z INFO # llrender/llglslshader.cpp(195) LLGLSLShader::dumpStats : deferred/skyF.glsl
2025-11-26T05:50:25Z INFO # llrender/llglslshader.cpp(198) LLGLSLShader::dumpStats : =============================================
2025-11-26T05:50:25Z INFO # llrender/llglslshader.cpp(215) LLGLSLShader::dumpStats : Triangles Drawn: 351 (0.07 pct of total, 2.856 million/sec)
2025-11-26T05:50:25Z INFO # llrender/llglslshader.cpp(216) LLGLSLShader::dumpStats : Binds: 1 (0.20 pct of total)
2025-11-26T05:50:25Z INFO # llrender/llglslshader.cpp(217) LLGLSLShader::dumpStats : SamplesDrawn: 4999789 (6.64 pct of total, 40.688 billion/sec)
2025-11-26T05:50:25Z INFO # llrender/llglslshader.cpp(218) LLGLSLShader::dumpStats : Time Elapsed: 122880 (5.67 pct of total, 0.12288 ms)

Related Issues

• Please link to a relevant GitHub issue for additional context.
  • Bug Fix: Link to an issue that includes reproduction steps and testing guidance.
  • Feature/Enhancement: Link to an issue with a write-up, rationale, and requirements.

Issue Link:

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Checklist

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• I have provided a clear title and detailed description for this pull request.
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• 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.
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• 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

Post Process Quality slider now controls color precision of post processing rendering. Previous slider now named Glow quality.