I learned how to make a 3D ray tracer from the awesome book The Ray Tracer Challenge.
This ray tracer is parallelized with C++ execution policies and has shadows, reflection, refraction, transparency, various patterns, and the Fresnel effect.
The project files that generate pictures like those above are in src/projects. Pick a file in there to render and run
cmake -DCMAKE_BUILD_TYPE=Release -B build && cmake --build build && ./build/src/projects/[filename] && open [filename].ppm