rt-go

rt-go is a small path tracer written in Go. Scenes are described with JSON and can contain spheres, boxes, quads, triangles, OBJ meshes, matte/metal/glass/plastic materials, and emissive lights.

Features

Rendering basics:

• CPU path tracing
• Antialiasing
• Gamma correction
• Cosine-weighted diffuse sampling
• Mixture PDFs for combining material and light sampling
• Direct light sampling
• Russian roulette path termination
• Configurable image size, samples, max depth, camera, and output path
• PPM image output with live scanline updates

Scene objects:

• Spheres
• Quads
• Boxes
• Triangles
• Triangle meshes
• OBJ model loading
• MTL material loading
• Smooth OBJ normals

Materials and lights:

• Lambertian matte materials
• Texture support: solid, checker, image, noise
• sRGB image texture loading with bilinear filtering
• Texture UV scale, offset, and rotation
• OBJ texture coordinates and MTL diffuse texture maps
• Metal materials
• Textured metal materials
• Dielectric glass materials
• Tinted glass materials
• Rough/frosted glass materials
• Glossy plastic materials
• Diffuse light materials
• One-sided emissive lights
• Weighted sampling targets

Transforms:

• Translation
• Rotation

Performance:

• Parallel scanline rendering
• BVH acceleration

Tools:

• JSON scene files
• Simple browser viewer

Usage

Place an OBJ model in:

models/figurine.obj

If the model has a material file, place it in the same folder and make sure the OBJ points to it with mtllib.

Render a JSON scene:

go run . -r examples/gallery.json

This writes:

image.ppm

Edit a JSON scene file to change the camera, render quality, objects, materials, and lights.

Other example scenes are in examples/.

See sceneGuide.md for a guide on how to design a scene.

For the browser viewer:

go run . -v examples/gallery.json

Then open:

http://localhost:8080

Notes

Large OBJ files can take time to load because the renderer parses the mesh and builds a BVH before rendering.

Scenes are defined with JSON files in examples/.

Increase render.samples in a JSON scene file for a cleaner image. Higher sample counts reduce noise but take more time to render.