ROSE ENGINE

A rose engine is the lathe that cuts guilloche, the woven ornament on the face of a pocket watch. It works by moving a cutter against a rotating plate. Everything it draws is a rose curve.

This cartridge points one at you.

You are a burnisher loose on the plate. The lathe starts at the rim and works inward, cutting a figure around you. Fresh metal is black and it is hot, and it will end your dial. A moment later it cools to grey and becomes finished ornament you can cross freely. Survive until the figure closes and the dial is yours.

The figures are computed, not drawn

There is no picture of any dial anywhere in the ROM. The cutter follows r = band + amp x cos(petals x angle + phase), which is the equation of a rose. The band walks from the rim to the centre across the round, and the phase advances a little every revolution. That drift is the rose engine's own index, and it is what turns a single closed curve into a woven dial instead of one line retraced forever.

Five numbers define a cut. The cartridge draws them itself, so you are not working through a set of authored levels.

Why it can do this on a Game Boy

The play area is a 128x96 framebuffer assembled from 192 individually addressed background tiles, which is what lets an arbitrary curve be engraved anywhere on it. A Game Boy draws forty sprites. A rose needs rather more than forty points on screen at once, so the ornament lives in the background instead, where it is also permanent. That is closer to what the real machine does anyway. It does not spray its figure into the air. It cuts it into the work, and the cut stays.

Scoring

Score climbs while you survive, and climbs four times faster while you are working close to the cutter. Hiding in a corner is safe. It is not how you get a score.

What you get

• roseengine.gb, a 32,768 byte ROM only cartridge with a valid header. Runs in any Game Boy emulator and writes to a flash cart like any other .gb file.
• Endless play and the higher difficulty tiers. The free browser version above is six dials on the first tier.
• A readme and a plain licence that lets you stream and monetise video of it with no separate permission.

Said plainly

• This has never run on physical Game Boy hardware. It was built and verified against an emulator. It is a standard 32 kB ROM only image and there is no reason to expect trouble, but we do not claim tests we have not run.
• Made with AI. Code and graphics were written with AI assistance, disclosed here and in the readme. The audio is procedural synthesis on the Game Boy's own sound hardware, which is not generative AI.
• The note table is derived from named frequencies and machine checked to within six cents of true pitch. Whether the music is pleasant is your call. Press SELECT to mute it.

Controls

D pad moves the burnisher. START begins and continues past a message. SELECT toggles sound.

More Game Boy cartridges and other work at csaf.itch.io.

On an Analogue Pocket

The download is a standard Game Boy ROM with no mapper, so on an Analogue Pocket it runs through the openFPGA Game Boy core. We have not run it on Pocket hardware ourselves, and there is no .pocket build in the download.