clouds.c: A Small, Feature-Rich Terminal Screensaver

Published

August 2026

Here’s a little project I cooked up with Fable over the course of about two weeks. Like my other projects with Claude, I led the design and iteration and had Claude do the technical implementation.

I’ve always enjoyed terminal screensavers like cbonsai and pipes.sh, but my background in R never gave me an opportunity to make my own— I’m just not great at writing in C. That made this a particularly good project to vibecode— I know how the renderer works, but wouldn’t have been able to get the volumetric logic running in C on my own (in a reasonable amount of time to make it worth doing as a project).

github: https://github.com/gbkorr/clouds.c

The presets nimbus, below, sol, and thunder.

Flags

The program is relatively feature-rich, and has quite a number of useful args.

Cloud Generation:
--coverage: Cloud sparsity.
--height: Cloud height; heigh values make for huge, billowing clouds.

Environment:
--time: Time of day; determines colors and sun elevation.
--preset: Settings preset. See §presets.
--azimuth: Horizontal (compass) sun angle; influences the direction of shading on the clouds.

Animation:
--wind: Speed of cloud movement.
--elevation: Camera Y position; 0.5 is at cloud level, so you can be above or below.
--yaw: Initial yaw angle, useful for looking into/away from the wind.
--pitch: Initial pitch angle.

Quality:
--quality: Number of raymarch steps. >60 not recommended unless prerendered with –loop.
--color: truecolor/256 ansi/mono color.
--ascii: Enable ASCII mode, not my favorite.
--ramp: Glyph ramp (transparent -> opaque) for ASCII rendering.
--fps: Desired frames per second; important for –loop.

Utility:
--interactive: Enable flight. See §flight.
--once: Render a single frame.
--loop: Prerender this many seconds, and loop playback. See §prerendering.
--output: Save --loop prerender to a file.
--file: Play saved file.

The four times, with default settings.

Flight!

Since the program already listens for keypressed to exit, interactive keyboard controls were a tiny addition. The arrow keys make you look around, and in --interactive mode, you fly in the direction you’re facing! In this mode -w controls your flight speed.

Sped-up footage of flight in interactive mode. The usual experience is much more leisurely.

Prerendering

Volumetric rendering is computationally expensive, and you don’t really want a screensaver making your CPU chug. I came up with a simple solution: just prerender a set number of frames and then loop them. This comes with the added benefit of being able to save the frames to play later.

30 fps 4-second looped animation:

./clouds --loop 4 --fps 30

Export to file and play file:

./clouds -loop 4 --fps 30 -o demo.clouds
./clouds --file demo.clouds

Colors

The project also supports a 256-color fallback for terminals without truecolor (or select it manually with --color 256). This color banding on this is GNARLY, I think I like it even more than truecolor.

Web Demo

Because it’s 2026, I was able to make a webdemo in 10 minutes with a quick oneshot prompt to “compile it to WASM and make a drop-in iframe”. So now you can pull it up in a browser window if you don’t feel like compiling for use in the terminal1.

https://gbkorr.github.io/gbkorr/clouds/clouds.html?ARGS

ARGS has format e.g. clouds.html?coverage=0.5&elevation=0&ascii=true. –color, loop, presets, and interactive mode aren’t implemented. Use ctrl +/- to increase/decrease resolution. I recommend zooming in a bit or making your browser window small, since it’s not designed to look good at super high resolution.

Footnotes

  1. Of course, it’s still a project designed for the terminal and this web version won’t be getting any updates. But it’s cool to have.↩︎