Toy Path Tracer

Toy path tracer for my own learning purposes, using various approaches/techs. Somewhat based on Peter Shirley's Ray Tracing in One Weekend minibook (highly recommended!), and on Kevin Beason's smallpt.

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

• 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

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

Implementations I'm playing with (again, everything is in toy/learning/WIP state; likely suboptimal) are below. These are all on a scene with ~50 spheres and two light sources, measured in Mray/s.

• CPU. Testing on "PC" AMD ThreadRipper 1950X 3.4GHz (SMT disabled, 16c/16t) and "Mac" mid-2018 MacBookPro i9 2.9GHz (6c/12t):
  • C++ w/ some SSE SIMD: PC 187, Mac 74, iPhone X (A11) 12.9, iPhone SE (A9) 8.5
  • C++: PC 100, Mac 35.7
  • C# (Unity with Burst compiler w/ some 4-wide SIMD): PC 133, Mac 60. Note that this is an early version of Burst.
  • C# (Unity with Burst compiler): PC 82, Mac 36. Note that this is an early version of Burst.
  • C# (.NET Core): PC 53, Mac 23.6
  • C# (Mono with optimized settings): Mac 22.0
  • C# (Mono defaults): Mac 6.1
  • WebAssembly (single threaded, no SIMD): 4.5-5.5 Mray/s on PCs, 2.0-4.0 Mray/s on mobiles.
• GPU. Simplistic ports to compute shader:
  • PC D3D11. GeForce GTX 1080 Ti: 1854
  • Mac Metal. AMD Radeon Pro 560X: 246
  • iOS Metal. A11 GPU (iPhone X): 46.6, A9 GPU (iPhone SE): 19.8

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

Building

• C++ projects:
  • Windows (Visual Studio 2017) in Cpp/Windows/TestCpu.sln. DX11 Win32 app that displays result as a fullscreen CPU-updated or GPU-rendered texture.
  • Mac/iOS (Xcode 9) in Cpp/Apple/Test.xcodeproj. Metal app that displays result as a fullscreen CPU-updated or GPU-rendered texture. Should work on both Mac (Test Mac target) and iOS (Test iOS target).
  • WebAssembly in Cpp/Emscripten/build.sh. CPU, single threaded, no SIMD.
• C# project in Cs/TestCs.sln. A command line app that renders some frames and dumps out final TGA screenshot at the end.
• Unity project in Unity. I used Unity 2018.2.13.