Moyun: a sheet of rice paper that breathes

A sheet of rice paper that breathes. Ink runs on a real-time fluid simulation in your GPU, every stroke plays a guqin note, and an invisible hand paints a Chinese landscape that has never existed before — then signs it with a poem and a seal. That is Moyun, and the whole piece is one HTML file. No libraries, no images, no audio files.

Watch it and a brush you cannot see paints in the classical order: distant hills, the main peak's outline, texture strokes, washes, moss dots, then pines, water, a fishing boat, birds, a cinnabar sun, a poem and a seal. Each painting is generated fresh, seeded, never the same twice.

Paint it yourself and the brush responds to speed. Slow strokes are wet and heavy; fast strokes are thin and dry. Each stroke is one dip of ink, so it runs dry into flying-white streaks — the brushwork calligraphers chase. There is a clear-water brush too: stir a finished painting and watch the ink swirl apart and settle again.

Every stroke you draw plays a note on a pentatonic guqin, synthesized with Karplus–Strong plucked strings, so nothing you make is ever out of tune.

The simulation is the real thing, not a filter. Incompressible Navier–Stokes in WebGL2 fragment shaders: curl, vorticity confinement, divergence, Jacobi pressure iterations, semi-Lagrangian advection. Ink stores free ink, cinnabar, water and settled ink in one texture; water diffuses anisotropically along procedural paper fibre; dried ink only moves again when re-wetted. The paper's grain is baked once per resize, light and dark themes follow your system, and night turns the ink to moonlight. A landscape that has never existed before, painted while you watch, in a browser tab. https://github.com/axtonliu/moyun

■ Filed from The Foundry: the tools wing of the city.