Skip to content

Home

RayON — animated prism logo with light rays dispersing into a spectrum

A CUDA & OptiX path tracer with real-time progressive sampling, volumetric clouds and ray-marched shapes

What is RayON?

RayON is an educational and experimental path tracer written in C++17 and CUDA. It started as a re-implementation of the classic Ray Tracing in One Weekend series and grew into an interactive renderer that holds 60 frames per second while the camera moves and accumulates thousands of samples per pixel when it stops. It is used as teaching material in the ISC 302 High-Performance Computing course at HES-SO Valais.

Two GPU back-ends share one scene description and one GUI, each in an offline and an interactive flavour. No recompilation is needed to switch between them (-m 2 to -m 5):

OptiX (hardware ray tracing)

Triangles on the RT cores, custom intersectors for spheres, rectangles and SDF shapes, an AI denoiser for motion frames and a regulator that trades resolution for frame rate. The default when the OptiX SDK is found.

CUDA (software ray tracing)

One thread per pixel, a BVH traversed with an iterative stack, persistent random states and a float accumulation buffer that never leaves the GPU. Runs everywhere CUDA runs.

Interactive mode

SDL2 window with mouse orbit, pan and zoom, a Dear ImGui panel for every rendering parameter, scene switching with the arrow keys, HDR skies, and a button that writes the camera and the light settings back into the scene file.

CPU renderers archived

The original CPU rendering back-ends (sequential and multi-threaded) live on the legacy/cpu-renderer branch. The main branch is GPU only.

What it renders

  • Materials: Lambertian, mirror, rough mirror, glass, GGX anisotropic conductors with measured complex IOR, thin-film interference, clear coat, area and sphere lights, and a volume material for clouds and smoke (delta tracking, Henyey–Greenstein phase function, volumetric shadow rays).
  • Geometry: spheres, rectangles, triangles, Wavefront OBJ meshes with MTL materials and UV textures, procedurally displaced spheres, ten ray-marched signed distance primitives, and volumes shaped by a mesh, by procedural noise or by an OpenVDB density grid.
  • Light transport: next event estimation with multiple importance sampling, a Sobol' low-discrepancy sampler with Owen scrambling, Russian roulette, adaptive (converged-pixel) sampling, a BVH built with the surface area heuristic.
  • Scenes: a plain YAML format with 24 bundled examples, from a Cornell box to the Stanford bunny as a cumulus cloud.

Sample renders

The Stanford bunny rendered as a cumulus cloud on a ground plane
Cloud bunny — the volume material: a mesh shaped by noise, lit by a sun with volumetric shadow rays. Scene 17_cloud_bunny.yaml.
The OpenVDB bunny cloud density grid rendered in RayON
VDB bunny — the same transport on a density grid from OpenVDB, the reference image of the pbrt book. Scene 17_vdb_bunny.yaml.
Ten ray-marched signed distance shapes in a studio room
SDF gallery — mandelbulb, death star, cut hollow sphere, torus, octahedron, pyramid and friends, sphere-traced on both back-ends. Scene 18_sdf_shapes.yaml.
Cornell box with area light and colour bleeding
Cornell box — diffuse colour bleeding and soft shadows from a rectangular area light, resolved by next event estimation.
Anisotropic metal and glass spheres
Anisotropic metals and glass — GGX microfacet conductors with measured spectral Fresnel next to dielectrics.
Thin film shader
Thin film — soap bubbles and oil slicks from the Airy interference formula.

Quick start

# Build (CMake ≥ 3.20, a C++17 compiler, the CUDA toolkit; SDL2 and the OptiX SDK are optional)
mkdir -p build && cd build
cmake .. --fresh
make -j$(nproc)

# Run from build/ — the OptiX programs and the HDR skies are found relative to this directory.
# Interactive OptiX when available, else interactive CUDA, else offline CUDA.
./rayon

# Pick a mode explicitly: 2 = CUDA offline, 3 = CUDA interactive, 4 = OptiX offline, 5 = OptiX interactive
./rayon -m 4 -s 512 -r 1080 --scene ../resources/scenes/17_cloud_bunny.yaml

See Getting Started for the full setup, the command-line options and the list of bundled scenes, or YAML Scene Format to write your own.

Explore the docs

Section What you'll find
How It Works The math: rendering equation, materials, BVH, sampling, Sobol', MIS, optimisations
Architecture Scene system, CUDA renderer internals, the progressive pipeline
Features Interactive mode, YAML scenes, lights, volumes, SDF shapes, OBJ loading, HDR skies
Gallery Renders from the bundled scenes
Performance Benchmarks, speedups, tuning tips
Development History How the project grew, commit by commit