Procedural infinite city written 100% by Opus 5.5 runs in-browser via WebGPU
jason_mayes · x · 2026-10-09
Developer Ryan Sael unveiled Gigacity, a fully procedural, endlessly expanding city written 100% by Claude Opus 5.5, running in real time in the browser via WebGPU. It builds on mrdoob's Three.js port of Unity's Megacity (GDC 2019) demo, which hits 45 fps on a MacBook Air M1 compressed to just 75 MB.
Technical highlights:
- No modeled assets: a single seed flows through a chain of hash-based rules — same seed, same city, down to which rooms are lit
- Street grid every 170 m self-determines width; blocks split into lots, with merged lots forming the tallest towers
- Towers stack segments with crowns; heights come from a smooth field over the map
- Rooms behind glass are drawn per pixel — shader traces sightlines into rooms with floors, blinds and furniture for parallax
- Traffic runs on fixed-height bidirectional sky lanes; car positions depend only on time, making thousands of cars nearly free
- Seed control, day/night, graphics presets, and multiple camera modes included
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