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Toy path tracer I did in 2018 for my own learning purposes. Somewhat based on Peter Shirley'sRay Tracing in One Weekend minibook (highly recommended!), and on Kevin Beason'ssmallpt.

I decided to write blog posts about things I discover as I do this:

• Part 0: Intro
• Part 1: Initial C++ and walkthrough
• Part 2: Fix stupid performance issue
• Part 3: C#, Unity and Burst
• Part 4: Correctness fixes and Mitsuba
• Part 5: simple GPU version via Metal
• Part 6: simple GPU version via D3D11
• Part 7: initial C++ SIMD & SoA
• Part 8: SSE SIMD for HitSpheres
• Part 9: ryg optimizes my code
• Part 10: Update all implementations to match
• Part 11: Buffer-oriented approach on CPU
• Part 12: Buffer-oriented approach on GPU D3D11
• Part 13: GPU thread group data optimization
• Part 14: Make it run on iOS
• Part 15: A bunch of path tracing links
• Part 16: Unity C# Burst optimization
• Part 17: WebAssembly

Note: it can only do spheres, no bounding volume hierachy of any sorts, a lot of stuff hardcoded.

Performance numbers in Mray/s on a scene with ~50 spheres and two light sources, running on the CPU:

More detailed specs of the machines above are:

• Ryzen 5950: AMD Ryzen 5950X (3.4GHz, 16c/32t), Visual Studio 2022.
• AMD TR1950: AMD ThreadRipper 1950X (3.4GHz, SMT disabled - 16c/16t), Visual Studio 2017.
• MBP 2021: Apple MacBook Pro M1 Max (8+2 cores), Xcode 13.2.
• MBP 2018: Apple MacBook Pro mid-2018 (Core i9 2.9GHz, 6c/12t).
• MBA 2020: Apple MacBook Air 2020 (Core i7 1.2GHz, 4c/8t).
• iPhone 11: A13 chip.
• iPhone X: A11 chip.
• iPhone SE: A9 chip.

Software versions:

• Unity 2021.3.16. Burst 1.6.6 (safety checks off). C# testing in editor, Release mode.
• Mono 6.12.

And on the GPU, via a compute shader in D3D11 or Metal depending on the platform:

A lot of stuff in the implementation istotally suboptimal or using the tech in a "wrong" way.I know it's just a simple toy, ok :)

• C++ projects:
  • Windows (Visual Studio 2017) inCpp/Windows/ToyPathTracer.sln. DX11 Win32 app that displays result as a fullscreen CPU-updated or GPU-rendered texture.Pressing G toggles between GPU and CPU tracing, A toggles animation, P toggles progressive accumulation.
  • Mac/iOS (Xcode 10) inCpp/Apple/ToyPathTracer.xcodeproj. Metal app that displays result as a fullscreen CPU-updated or GPU-rendered texture.Pressing G toggles between GPU and CPU tracing, A toggles animation, P toggles progressive accumulation.Should work on both Mac (Test Mac target) and iOS (Test iOS target).
  • WebAssembly inCpp/Emscripten/build.sh. CPU, single threaded, no SIMD.
• C# project inCs/TestCs.sln. A command line app that renders some frames and dumps out final TGA screenshot at the end.
• Unity project inUnity. I used Unity 2021.3.16.