Compile-Time Ray Tracer in Rust

Introduction

This in a Rust reimplementation of https://github.com/tcbrindle/raytracer.hpp. It tries to produce a ray traced image entirely at compile-time. This means the final render is stored directly in the binary without performing any computations at run-time.

This implementation extensively exploits const fn nightly features to see what is the current state of compile-time evaluation in Rust.

Current limitations of const fn

I tried to make this implementation close to the original, though, it was not always feasible. C++ version uses templates to make RayTracer class generic over a scene to allow for rendering two types of scenes: statically and dynamically created. The similar applies to a canvas. Unfortunately, it is not possible to use generic bounds to constraint type to have a const implementation of the trait, so I hardcoded type of scene with some code duplication for run-time and compile-time versions.

Another thing is that right now Rust doesn't support const function pointers and closures which are used in the original implementation within object surface property definitions. I have replaced them with trait.

Also, it isn't possible to use for loops to iterate over slices in const context as it requires const implementations of IntoIterator and Iterator traits for slices. A simple workaround is to use while loop with manual indexing.

Performance

It took almost 23 minutes to render above image at compile-time on my machine (Ryzen 7 1700). Peak compiler's memory usage reached 6.6GB. For comparison the run-time version executes in 1.4s on the same machine. It makes compile-time version 1000x slower. I was using rustc 1.45.0-nightly (7f65393b9 2020-05-01).