Kyoubic Relit

A CPU path tracer, adapted from Peter Shirley's "Ray Tracing in One Weekend" book series into a lightmap baker: renders triangle-soup OBJ meshes (no spheres/quads-only scene, unlike the books) and writes per-vertex irradiance instead of a pixel image, for use as Kyoubic's static lightmap bake backend (see tools/raytracer_weekend_bake.py in the parent repo).

Credit

The core ray tracing algorithms (vec3/ray math, BVH, materials, importance sampling / PDFs / MIS, constant medium, Perlin noise) are kinda copied from

• Ray Tracing in One Weekend
• Ray Tracing: The Next Week
• Ray Tracing: The Rest of Your Life

by Peter Shirley, Trevor David Black, and Steve Hollasch. https://raytracing.github.io/

The code, while be it based off the books, has been cleaned up and reformatted. It is still comparable, just, different. triangle.hpp, obj.{cpp,hpp}, and the lightmap-baking mode in bake.cpp, however, are NOT from in any of the books. I wrote those using the books code as a sort of lib to interface with hittable and material (obj.{cpp,hpp} are ported near-verbatim from Kyoubic but with minor tweaks to remove GLM dep). main.cpp is MOSTLY from the books too (cornell_box(), final_scene()) but also has add_box_light() and vulkanproject_scene() bolted on from OUTSIDE the book. Those load the real Kyoubic scene geometry and box-lights, as a sanity check render against the per-vertex bake. Everything else stays 1:1 with the books so its still comparable if you go read them yourself (which u should, theyre PEAK)

Building

Requirements

• CMake 3.15+, OR Python 3 with SCons (pip install scons)
• A C++17 compiler. MSVC/cl is the default on Windows, override with cxx= (SCons) or -DCMAKE_CXX_COMPILER= (CMake) if you want clang-cl, GCC (God forbid), whatever.

Build (SCons)

python -m SCons

or if u dont have MSC cl.exe and use clang instead

python -m SCons cxx=clang-cl

Build (CMake)

cmake -B build
cmake --build build

if u dont have MSC cl.exe/wanna use clang instead

cmake -B build -DCMAKE_CXX_COMPILER=clang-cl

Both produce two executables in build/[subfolder], where subfolder depends on your configurations and build system.

Kyoubic-Relit itself doesnt have a debug/release split. /O2/-O2 is always on, theres no config to pick here.

The parent Kyoubic engine repo DOES have a real debug/release split tho. see that repo's own README for how to build it in release mode.

raytracer is the books own standalone demo renderer (writes a PPM image) bake is the lightmap baker Kyoubic uses

tools/raytracer_weekend_bake.py in the parent Kyoubic repo expects bake.exe (or bake on non-Windows) to end up at tools/Kyoubic-Relit/bake[.exe] relative to the tools folder. IMPORTANT: copy or symlink the built binary there after building, or point BAKE_EXE in that script at wherever your build put it.

Usage as a standalone renderer

./build/raytracer > out.ppm

Renders whatever scene is hardcoded in main.cpp (see the books for how to swap scenes) to a PPM image on stdout.

Usage as a lightmap baker

You cant run ts directly (unless u use dark magic). Instead you should use tools/raytracer_weekend_bake.py in the parent repo, which builds the occluder/light-box argument list from a Kyoubic scene JSON and calls bake.exe with them. See the scripts docstring for the exact CLI it expects (iirc should be in the first or second comment in each file in Kyoubic/tools/*.py)