Ole-Morten Duesund
2af36e2ac0
The previous wording asserted design intent ('Kensler golfed [...] until
it hit the magic number', 'every typedef exists to land on 1337') without
a primary source. CLAUDE.md requires factual claims in committed artifacts
to be checked. The byte count is verified; intent is not. Rephrased to
note the observation ('suspiciously round', 'rarely lands by accident')
without claiming insight into the design process, and the obfuscation
breakdown is kept since the techniques are visible in the code itself.
101 lines
3.6 KiB
Markdown
101 lines
3.6 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 a
|
|
single C++ source file small enough to print on the back of a business
|
|
card.
|
|
|
|
> **`card.cc` is exactly 1337 bytes.** Yes, **leet**. Verify it yourself:
|
|
>
|
|
> ```sh
|
|
> $ wc -c card.cc
|
|
> 1337 card.cc
|
|
> ```
|
|
>
|
|
> That is suspiciously round — hand-golfed C++ rarely lands on a famous
|
|
> leet number by accident. The compression tricks all show their work:
|
|
> typedefs (`i` for `int`, `f` for `float`), operator overloads on
|
|
> `struct v` that turn `+` / `%` / `^` / `!` into vector math, and not
|
|
> a wasted space anywhere.
|
|
|
|
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/
|