Simon Willison’s Weblog

Pelican on a Bike—Raytracer Edition (via) beetle_b ran this prompt against a bunch of recent LLMs:

Write a POV-Ray file that shows a pelican riding on a bicycle.

This turns out to be a harder challenge than SVG, presumably because there are less examples of POV-Ray in the training data:

Most produced a script that failed to parse. I would paste the error back into the chat and let it attempt a fix.

The results are really fun though! A lot of them end up accompanied by a weird floating egg for some reason - here's Claude Opus 4:

I think the best result came from GPT-5 - again with the floating egg though!

I decided to try this on the new gpt-5-codex-mini, using the trick I described yesterday. Here's the code it wrote.

./target/debug/codex prompt -m gpt-5-codex-mini \
  "Write a POV-Ray file that shows a pelican riding on a bicycle."

It turns out you can render POV files on macOS like this:

brew install povray
povray demo.pov # produces demo.png

The code GPT-5 Codex Mini created didn't quite work, so I round-tripped it through Sonnet 4.5 via Claude Code a couple of times - transcript here. Once it had fixed the errors I got this:

That's significantly worse than the one beetle_b got from GPT-5 Mini!

# 4:51 pm / 3d, ray-tracing, ai, generative-ai, llms, pelican-riding-a-bicycle, gpt-5