Simple Path Tracer (CPU Embree + GPU OptiX)

A lightweight physically-based path tracing renderer with CPU and GPU backends, focused on clarity, correctness, and experimentation.

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Features

Overview

This project implements a Monte Carlo path tracer with two rendering backends:

• CPU backend using Intel Embree 4 and TBB
• GPU backend using NVIDIA OptiX with a wavefront-style pipeline

The CPU implementation serves as a reference, while the GPU backend is designed for performance exploration and learning modern GPU path tracing architecture.

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Features

Rendering

• Monte Carlo path tracing
• Progressive accumulation
• Physically-based materials (diffuse / metal / dielectric / emissive)
• Environment lighting (procedural sky + optional HDR environment map)
• Directional light support (GPU)
• Resolve stage with tonemapping + gamma correction

Backends

CPU (Embree + TBB)

• High-quality BVH traversal via Embree
• Tile-based rendering
• Multi-core parallelism with TBB

GPU (OptiX)

• OptiX ray traversal and intersection
• Wavefront-style path tracing (trace → shade → resolve)
• Explicit path state and queues
• Designed for further divergence reduction and queue classification

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Controls

Camera

• W / A / S / D – move camera
• Mouse – look around
• ESC – exit

Backend Switching

• G – toggle rendering backend
  • CPU Embree path tracer
  • GPU OptiX wavefront path tracer

Switching backends resets accumulation automatically.

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Rendering Pipeline (High Level)

CPU Backend

1. Scene setup
2. Embree BVH build
3. TBB tile dispatch
4. Path tracing
5. Progressive accumulation
6. Tonemap + gamma
7. Display

GPU Backend (OptiX)

1. Ray generation / path initialization
2. OptiX trace → hit records
3. Shade stage (hit / miss, materials, environment, direct light)
4. Accumulation
5. Resolve stage:
   • average samples
   • tonemapping
   • gamma correction
6. Display

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Color & Brightness Notes

The renderer accumulates linear HDR radiance.

Final output is produced in the resolve stage using:

• exposure scaling
• tonemapping (e.g. Reinhard)
• gamma correction (sRGB, 1/2.2)

If the image appears too dark or too bright, adjust exposure or environment intensity, not BRDF parameters.

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Build

Requirements

• Windows + Visual Studio 2019/2022
• CMake 3.20+
• vcpkg
• CUDA Toolkit (for GPU backend)
• NVIDIA OptiX SDK (for GPU backend)

Dependencies (vcpkg)

vcpkg install embree glm glfw3 glew tbb stb