Ole-Morten Duesund
f8b7ff475c
Preserves Andrew Kensler's original card.cc verbatim and adds: - CMakeLists.txt building both the original and a de-obfuscated variant (card_explained.cc) that produces a visually identical render - A heavily annotated rewrite explaining the vector ops, ray-sphere intersection, soft shadows, depth of field, and reflection recursion - Rendered sample output (docs/aek.png) embedded in the README - CLAUDE.md establishing the "never modify card.cc" rule for future work
88 lines
3.2 KiB
Markdown
88 lines
3.2 KiB
Markdown
# card-raytracer
|
|
|
|
A study of [Andrew Kensler's "business card raytracer"][aek] — a complete
|
|
recursive path-tracer with soft shadows, depth of field, anti-aliasing,
|
|
reflections, a checker floor, and a sky gradient, all crammed into ~1337
|
|
characters of obfuscated C++ small enough to print on the back of a
|
|
business card.
|
|
|
|
The original code is preserved verbatim as [`card.cc`](card.cc). A
|
|
de-obfuscated, heavily-annotated rewrite lives in
|
|
[`card_explained.cc`](card_explained.cc). Both produce the same image:
|
|
|
|
|
|
|
|
The spheres spell **a · e · k**, Andrew Kensler's initials, encoded as a
|
|
9-column bitmap in the `G[]` array of the original source.
|
|
|
|
## Quick start
|
|
|
|
Requires a C++14 compiler, CMake ≥ 3.16, and (optionally) `netpbm` for
|
|
PPM → PNG conversion.
|
|
|
|
```sh
|
|
cmake -S . -B build
|
|
cmake --build build
|
|
|
|
# Render with the original (PPM, 786 KiB, ~6 s on a modern laptop)
|
|
./build/card > aek.ppm
|
|
|
|
# Or via the convenience target:
|
|
cmake --build build --target image # → build/aek.ppm
|
|
cmake --build build --target image_explained # → build/aek_explained.ppm
|
|
|
|
# View it (PPM is supported by most image viewers; or convert):
|
|
pnmtopng aek.ppm > aek.png
|
|
```
|
|
|
|
## What's interesting about it
|
|
|
|
The whole renderer is built on **operator overloading**: a single `struct v`
|
|
provides `+` (add), `*` (scale), `%` (dot product), `^` (cross product), and
|
|
unary `!` (normalise). Once those are in place, the entire rendering
|
|
pipeline — sphere intersections, reflection vectors, Phong shading,
|
|
checker-pattern tile lookup, camera basis construction — collapses into
|
|
just a handful of expressions.
|
|
|
|
Other tricks worth admiring:
|
|
|
|
- **Soft shadows for free**: the light position is jittered each call, so
|
|
averaging 64 samples per pixel produces a real penumbra without any
|
|
area-light formalism.
|
|
- **Depth of field for free**: the camera origin is also jittered across
|
|
a 99-unit "lens" each sample, so points off the focal plane go blurry.
|
|
- **Anti-aliasing for free**: sub-pixel jitter on the ray direction.
|
|
|
|
The same 64-sample loop pays for all three at once.
|
|
|
|
A line-by-line walkthrough of the algorithm is the long-form
|
|
[comments inside `card_explained.cc`](card_explained.cc).
|
|
|
|
## Layout
|
|
|
|
```
|
|
.
|
|
├── card.cc # original, untouched — do not edit
|
|
├── card_explained.cc # de-obfuscated, documented rewrite
|
|
├── CMakeLists.txt
|
|
├── docs/
|
|
│ └── aek.png # published render
|
|
├── README.md
|
|
└── CLAUDE.md # working notes for AI assistance
|
|
```
|
|
|
|
## Credits
|
|
|
|
- Original raytracer: [Andrew Kensler][aek-home] ("aek").
|
|
- Excellent walkthrough that inspired this study:
|
|
Fabien Sanglard, [_Decyphering The Business Card Raytracer_][aek].
|
|
|
|
## Licence
|
|
|
|
The original `card.cc` is reproduced as-is from publicly published material
|
|
for educational purposes; credit and copyright belong to Andrew Kensler.
|
|
The supporting files in this repository (CMake, README, de-obfuscated
|
|
rewrite) are placed in the public domain by the repository author.
|
|
|
|
[aek]: https://fabiensanglard.net/rayTracing_back_of_business_card/
|
|
[aek-home]: https://www.cs.utah.edu/~aek/
|