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Path tracer

This is an experimental path tracer using C++20 and SYCL for acceleration on devices like FPGA or GPU by using a direct implementation.

img

This is using triSYCL for now but it might work even better on some other SYCL implementations. Contributions and optimizations welcome!

The main focus here is to study how to replace classic features like pointers or dynamic polymorphism that does not work (well) on heterogeneous with more modern constructs such as std::variant and std::visit.

Features

  • motion blur;
  • depth of field;
  • materials:
    • smoke;
    • textures;
    • Lambertian material;
    • dielectric material;
    • metallic roughness;
    • light;
  • geometry:
    • spheres;
    • triangles;
    • x/y/z-rectangles;
    • boxes;

Required dependancies

In addition to triSYCL, this project requires the following dependancies:

  • the stb image manipulation library;

On Linux, there is a good chance it can be installed with your package manager :

On Ubuntu/Debian :

sudo apt install libstb-dev

On Archlinux, install the stb package from AUR.

Compiling

Clone the reposity such as with:

git clone [email protected]:triSYCL/path_tracer.git

Create a build directory for example inside the cloned repository and jump into it.

From there, assuming you have the https://github.com/triSYCL/triSYCL repository somewhere, run:

cmake .. -DCMAKE_MODULE_PATH=<absolute_path_to>/triSYCL/cmake

The project defaults to a Release build configuration. If you wish to debug, configure your build settings as follow:

cmake .. -DCMAKE_BUILD_TYPE=Debug -DCMAKE_MODULE_PATH=<absolute_path_to>/triSYCL/cmake

It is also possible to build with https://github.com/triSYCL/sycl or https://github.com/intel/llvm/tree/sycl

cmake .. --DCMAKE_MODULE_PATH=<absolute_path_to>/triSYCL/cmake -DTRISYCL_OPENMP=OFF -DSYCL_CXX_COMPILER=<path_to_sycl_build>/bin/clang++ -DSYCL_DEVICE_TRIPLE=fpga64_sw_emu
# the triple fpga64_sw_emu is only available with https://github.com/triSYCL/sycl

The triSYCL cmake path and options are required for some cmake macros they define.

For FPGA execution you might add -DUSE_SINGLE_TASK=ON on the previous cmake configuration to use a SYCL execution based on a .single_task() instead of .parallel_for(), probably more efficient on FPGA.

Build the project with:

cmake --build . --verbose --parallel `nproc`

This creates the executable.

Running

Now you can run the path tracer with:

time ./sycl-rt

This results in the image out.png produced by the path tracer.

Bibliography

Some references that were tremendously useful in writing this project:

  1. Path tracing

  2. Ray Tracing in One Weekend - Peter Shirley

  3. Ray Tracing: The Next Week - Peter Shirley

  4. Ray-tracing in a Weekend with SYCL: Basic sphere tracing -- Georgi Mirazchiyski

  5. Ray-tracing in a Weekend with SYCL Part 2: Pixel sampling and Material tracing -- Georgi Mirazchiyski

  6. CppCon 2018: Mateusz Pusz, “Effective replacement of dynamic polymorphism with std::variant”

  7. Bartek's coding blog: Runtime Polymorphism with std::variant and std::visit

  8. Intersection of a Ray/Segment with a Triangle