This project renders a simple 3D scene entirely at compile time and intentionally fails compilation to display the resulting ASCII art inside compiler error messages. There is no successful executable; the “output” is the error log.

• Builds a constexpr ray tracer (spheres, lighting, shadows) in C++20.
• Converts the rendered image to ASCII (80x40).
• Forces compilation to fail so the ASCII art appears in errors.
• Provides a post-processor to clean the error stream into readable ASCII.

• raytracer.cpp — constexpr ray tracer and error emitter.
• tools/clean_errors.py — extracts ASCII art from LineTag<...> errors.
• tools/render.sh — builds, saves raw errors, and writes cleaned image.

• Clang (C++20). GCC is not recommended for the error-emission approach used here.
• Python 3 (for the post-processor).

clang++ -std=c++20 -fconstexpr-steps=10000000 -ferror-limit=0 raytracer.cpp

This prints a wall of errors containing LineTag<...> type instantiations. Each LineTag<...> encodes one line of the ASCII image.

clang++ -std=c++20 -fconstexpr-steps=10000000 -ferror-limit=0 raytracer.cpp 2>&1 | tools/clean_errors.py

./tools/render.sh

This writes:

• raw.txt — full compiler error output
• image.txt — cleaned ASCII art

You can pass custom filenames:

./tools/render.sh raw_output.txt image_output.txt

C++20 requires static_assert messages to be string literals. Because we need a computed string, we encode each output line as a type instead:

• Each line becomes LineTag<' ','.',':',...>.
• static_assert fires on a dependent type so Clang prints the full type.
• The post-processor strips punctuation and reconstructs the ASCII art.

The scene is a small collection of spheres with a single point light:

• Ground sphere for the floor
• Multiple spheres with different sizes and specular values
• Shadows for depth perception

You can tweak the scene in raytracer.cpp:

• spheres array (positions, radius, albedo, specular)
• light_pos and light_color
• camera / viewport parameters

If you hit constexpr step limits, increase the steps:

clang++ -std=c++20 -fconstexpr-steps=20000000 -ferror-limit=0 raytracer.cpp

• This project intentionally fails to compile.
• The ASCII output is the error log (or the filtered output via clean_errors.py).
• For presentations/demos, use raw.txt and image.txt side by side.

MIT