Vaibhav Rathod's Notes

PathTracer Learning - Project - Vulkan RT

2 min read

  • Goal

    • Port the CPU path tracer to Vulkan ray tracing
    • Integrate with Godot’s rendering pipeline

  • Milestones

    • Milestone 1: Vulkan setup + triangle in RT
      • Initialize Vulkan with RT extensions
      • Create BLAS from a single triangle
      • Create TLAS with one instance
      • Write minimal rgen + rchit + rmiss shaders
      • Display result in a window
    • Milestone 2: Full scene + BVH
      • Load OBJ, create BLAS per mesh
      • Create TLAS with all instances
      • Pass vertex/index data to closest-hit shader via device address
      • Reconstruct hit position and normal in shader
    • Milestone 3: Path tracing on GPU
      • Implement iterative path tracing in rgen shader
      • Cosine-weighted sampling in GLSL
      • Temporal accumulation (ping-pong buffers)
      • Display accumulated result
    • Milestone 4: Full PBR + NEE
      • GGX BRDF in GLSL
      • Shadow rays for direct lighting
      • MIS weighting
    • Milestone 5: Godot integration

  • Key Technical Challenges

    • Vertex data access in closest-hit shader
      • Use GL_EXT_buffer_reference to access vertex buffer by device address
      • Store per-instance buffer addresses in a storage buffer
      • Index by gl_InstanceCustomIndexEXT
    • Material data
      • Pack PBR parameters into a compact struct
      • Store in per-instance data buffer
      • Sample textures using gl_InstanceCustomIndexEXT as texture array index
    • Random number generation
      • PCG hash or Xorshift for per-pixel, per-sample RNG
      • Seed with gl_LaunchIDEXT.xy and frame counter

  • Performance Targets

    • 1080p @ 60fps with 1 spp + denoising
    • BLAS build: < 1ms per frame for dynamic objects
    • TLAS rebuild: < 0.5ms per frame

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