Progressive Monte Carlo GPU path tracer written in Slang and C++ using Vulkan.
8 billion instances of Suzanne:
- Sphere primitives
- Triangle primitives + OBJ loader
- BSDF mmaterial support for ior and metallic
- CPU BVH construction and GPU traversal
- Mesh lights
- Gaussian Splat primitives + PLY loader
- Progressve path tracing with temporal accumulation
- Transforms (location, rotation, scale)
- Instancing
- TLAS/BLAS separation
- Mixed node types (transform, primitive, binary AABB, 8-wide KDOP)
- Nested instances
This section does not cover every aspect of the engine. (e.g. Triangle, and Sphere intersections will not be covered)
Transforms are the easiest way to make instances of BLAS. Transforms have a single child that can be any node type (Inner node, Primitive, other transform, etc.).
Since transforms point to an arbitrary child, it allows for construction of nested instances.
The following will use these definitions:
Primitive: a single triangle, sphere, gaussian splat, etc.
Instance: a collection of primitives contained in a BLAS.
Collection: group of instances in an acceleration structure.
Note: collections can contain other collections. This node structure means the following tree is possible:
root TLAS
├── transform
| └── pointer to Collection 1
└── transform
└── pointer to Collection 1
Collection 1 TLAS
├── pointer to Instance BLAS
└── transform
└── pointer to Instance BLAS
Using this structure, an arbitrarily large number of primitives can be represented on a smaller footprint while also having a small build time.
For example: a N by N by N cube of Suzannes would contain N^3 Suzanne instances in a non-nested TLAS, but a nested TLAS can represent the same scene by repeating instances of collections of Suzannes.
This lowers the memory footprint and build time for scenes with repeated groups of instances,
allowing for much larger scenes in the same memory footprint and build-time constraints.
The PLY loader is adapted from 3D Gaussian Splatting in a Weekend.
Collisions with gaussian splat primitives are calculated using their covariance matrix and center.
The path tracer takes advantage of its Monte Carlo architecture to stochastically hit/miss splat primitives.
By averaging samples across many rays, the path tracer simulates alpha blending of many splats.
Read more about this type of gaussian splat ray tracing here: Stochastic Ray Tracing of Transparent 3D Gaussians
This is an incomplete list of references used when making this project.
Sun, Xin, et al. "Stochastic Ray Tracing of Transparent 3D Gaussians." arXiv preprint arXiv:2504.06598 (2025).
Feldman, Benjamin. (May 2026). “3D Gaussian Splatting in a Weekend”. bfeldman.me. https://bfeldman.me/3dgs-weekend/.
Arman Uguray. "Ray Tracing: GPU Edition". https://raytracing.github.io/gpu-tracing/book/RayTracingGPUEdition.html.
Vaidyanathan, Karthik, Sven Woop, and Carsten Benthin. "Wide BVH traversal with a short stack." Proceedings of the Conference on High-Performance Graphics. 2019.