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NVIDIA OpenGL Support: Launch, Stability & Optimizations

This document details the issues encountered when running the application on NVIDIA hardware and the solutions implemented to ensure a stable startup and high-performance execution.

I. Startup & Stability Fixes (Critical)

These issues prevented the application from launching or caused immediate crashes/invalid states on NVIDIA drivers.

1. Robust Texture Mipmap Allocation (Error 0x501)

  • Problem: The application could fail or render incorrectly during IBL map generation. NVIDIA drivers are strict about glTexStorage2D parameters. An incorrect levels calculation for high-resolution 4K textures triggered GL_INVALID_VALUE (0x501).
  • Fix: Implemented a precise mip-level formula: 1 + (int)floor(log2(fmax(width, height))) and added defensive range checks.
  • Result: Immediate resolution of 0x501 errors during the asynchronous loading phase.

2. Object Labeling & Initialization Sequence (Error 1282)

  • Problem: Calling glObjectLabel on objects immediately after glGen* caused "Unknown Object" errors. NVIDIA considers objects "uninitialized" until they are bound.
  • Fix: Reordered the sequence to ensure every object (VAO, VBO, Texture) is bound at least once before labeling.
  • Result: Clean debug logs and stable startup sequence.

II. Performance & Warning Cleanups

These changes addressed recurring performance warnings and optimized the rendering pipeline for NVIDIA's driver heuristics.

1. Dummy Texture Strategy (Unit Binding Cleanup)

  • Issue: Binding 0 to an active texture unit triggered "undefined base level" warnings and potential driver-side shader recompilations.
  • Fix: Introduced dummy_black_tex and dummy_white_tex (1x1 pixels). These are bound whenever a real texture (like HDR environment or Bloom) is pending or disabled.
  • Result: Perfectly clean debug logs even during asynchronous asset loading; stable shader execution.

2. VAO State Reconciliation (Shader Recompilation)

  • Issue: Frequent "Vertex shader recompiled based on GL state" (0x20092) warnings caused by indeterminate attribute divisor states across different VAOs.
  • Fix:
    • Explicitly called glVertexAttribDivisor(index, 0) for all non-instanced attributes in all VAOs.
    • Systematically disabled unused attribute arrays (indices 1-7) in specialized VAOs (Skybox, Billboards).
  • Result: Recompilation is now limited to a one-time startup JIT event, eliminating runtime stuttering.

3. Efficient Memory Placement (Buffer Movement)

  • Issue: Performance warnings (0x20072) regarding buffer migration between VIDEO and HOST memory during luminance reduction transfers.
  • Fix:
    • Caching: Luminance SSBOs are now persistent in the App struct to avoid per-frame allocation overhead.
    • Buffer Storage: Used glBufferStorage with GL_MAP_READ_BIT | GL_CLIENT_STORAGE_BIT to hint to the driver that these small readback buffers should stay in host-visible memory.
    • Fast Readback: Replaced mapping with glGetBufferSubData to minimize synchronization stalls for single-float transfers.
  • Result: Smooth asynchronous exposure adaptation without driver-staged copies.