MiTrace

MiTrace is a CPU-based path tracer written in C++20. It renders physically-accurate images by simulating light transport through GLTF scenes using Monte Carlo sampling. The renderer includes a Cook-Torrance BRDF, BVH acceleration, multi-threaded tile-based work distribution, and an optional real-time preview window. It's still work-in-progress so some rough edges are still there. ^^

Gallery

Hero Render

Featured Scenes

Features

Rendering Algorithms

• Cook-Torrance BRDF - GGX microfacet distribution, Schlick-Fresnel, Smith geometry masking, split diffuse/specular
• Russian-roulette path termination - configurable energy threshold to limit path depth
• Statistical firefly elimination - configurable threshold in standard deviations to clamp outlier samples

Performance

• Multi-threaded path tracing - work distributed across all CPU cores in configurable tiles
• BVH acceleration structure - SAH-based construction with configurable max triangles per leaf and max depth
• CPU affinity pinning - optional worker thread pinning for cache efficiency

Scene Features

• GLTF scene loading - .gltf files with multi-scene and multi-camera support
• PBR textures - base color, metallic/roughness, normal maps, occlusion, emissive
• Point lights - with configurable radius and color/intensity
• HDRI / environment lighting - loaded from GLTF or CLI-overridden; supports rotation and separate primary/secondary intensity

Output & Visualization

• Export formats - PNG, JPEG, HDR
• Live preview window - optional GLFW + ImGui + OpenGL real-time preview (5 FPS refresh); compile-time optional via ENABLE_PREVIEW_GUI

Architecture

MiTrace follows a three-stage pipeline:

1. Loader - Scene Import

Reads .gltf files and extracts scene data: meshes, materials, textures, cameras, lights, and transforms. Produces intermediate loader types.

2. Scene - Intermediate Representation

Converts loader types into a renderable scene: builds material cache, loads textures into memory, constructs BVH acceleration structures, and stores cameras/lights for path tracing.

3. Tracer - Path Solver

Multi-threaded Monte Carlo path tracer. Distributes work via a tile queue across worker threads. Each thread:

• Generates primary rays from the camera
• Traces rays through the scene (BVH intersection tests)
• Evaluates materials and lighting at hit points
• Samples indirect illumination recursively
• Accumulates contributions to a shared render buffer

4. Preview (Optional)

Live visualization during render via GLFW window + ImGui overlay. Periodically samples the accumulated render buffer and displays it at 5 FPS. Compile-time optional via ENABLE_PREVIEW_GUI CMake option.

Output

Accumulated render buffer is tone-mapped and exported to PNG, JPEG, or HDR format.

Dependencies

All dependencies are fetched automatically by CMake via FetchContent.

Library	Purpose
argparse	CLI argument parsing
nlohmann/json	GLTF JSON parsing
spdlog	Logging
GLM	Math (vectors, matrices)
stb	Image load/write
GLFW	Window/OpenGL context (preview only)
Dear ImGui	Preview UI (preview only)

Building

Requirements: CMake ≥ 3.16, a C++20-capable compiler, OpenGL development headers (for preview).

cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build --parallel

CMake options

Option	Default	Description
ENABLE_PREVIEW_GUI	ON	Build the live preview window
TARGET_ARCH	native	-march= target (e.g. x86-64, native)
CMAKE_BUILD_TYPE	Release	Release / RelWithDebInfo / Debug

Release and RelWithDebInfo compile with -Ofast -flto -march=<TARGET_ARCH>.
Debug compiles with -O0 -g -fsanitize=address,undefined.

The binary is written to build/MiTrace.

Usage

MiTrace <input.gltf> [options]

Example

# Render cornell box at 1080p, 256 spp, with live preview
./build/MiTrace assets/tests/cornell_box_test/cornell_box.gltf \
    -w 1920 -h 1080 -s 256 -b 8 \
    -o outputs/cornell.png \
    --preview

Output files that are not given an explicit name are auto-generated as outputs/render_<DDMMYYYY_HHMM>.png.

Blender Exporter

A Blender add-on for exporting scenes to GLTF in a format compatible with MiTrace is located in scripts/blender/mitrace_gltf_exporter/. A pre-packaged .zip for installation via Edit → Preferences → Add-ons → Install is provided at scripts/blender/mitrace_gltf_exporter.zip.

Roadmap

V1 Goals

• Break up the golf scene to be uploaded as 2 files (size limit)
• Proper low-roughness non-metals
• Add skybox loading from GLTF file
• Generalize the Texture class
• Test the Blender exporter
  • Skybox export
  • Lights export
• Add mesh-level BVH
• Add multiple light types
• Improve the light selection algorithm
• Add bidirectional path tracing
• Add alpha (non-physical) transparency
• Add light bending on transparency
• Integrate OpenImageDenoise

Completed

• Move the tracer back to the tracer directory
• Add camera selection
• Add GLTF scene selection
• Add skyboxes
• Fix the light radius problem
• Add debug render modes
  • Intersections: primary and total BVH and triangle tests
  • Material: albedo, metallic/roughness, geometric normal, shading normal
  • Contributions: direct only, indirect only, emission
  • Random color: per mesh, per triangle, per bounding volume
  • Other: bounces, depth, first-hit Fresnel/BRDF/PDF, reflected direction, pixel standard deviation