Pixel-level 2D physics experiments across scalar JavaScript, Web Workers, Wasm SIMD, Atomics, and resident WebGPU. The default lab visualizes density exchange, extinguishing and vaporization, lava-water solidification, acid corrosion, fuel ignition, and adhesive gel that fractures on impact in parallel.

This repository was extracted from mizchi/jsimd after commit fd849e3 so pixel-physics research can evolve independently from the general-purpose SIMD library.

Requirements: Node.js 24+, pnpm, Deno, just, and wasm-tools.

pnpm install
just test
just dev

Open:

http://127.0.0.1:5173/?run=pixel&runtime=worker-reaction-simd&size=512&occupancy=25&region=full

The separate rod/hinge experiment is available at http://127.0.0.1:5173/?run=rigid.

The same demo is deployed to https://mizchi.github.io/pixel-lab/?run=pixel&runtime=worker-reaction-simd&size=512&occupancy=25&region=full. GitHub Pages has no custom response-header configuration, so a site-scoped Service Worker adds the COOP/COEP headers required by SharedArrayBuffer; it is not part of the application bundle.

The reaction Worker uses a compact u32 cell ABI, active 2x2 movement, a dense SIMD thermal and chemistry pass, SharedArrayBuffer input, and OffscreenCanvas presentation. Other query-selectable backends retain scalar, sparse, SIMD, and WebGPU baselines.

Gel reuses the existing flags and variant bytes: resting gel bonds to wall, sand, stone, or wood; free gel accumulates fall momentum; and impact above the break threshold fractures the bond for an eight-tick cooldown before it can attach again. Its lateral flow is gated to one quarter of normal fluid flow, so this adds no per-cell buffer.

The optional Rigid Lab overlays a fixed-capacity SoA particle/constraint layer without changing the pixel ABI. Rods can share particles as hinges, break above a configured strain, collide with solid pixels, and bond to or detach from gel. A sparse temporary support raster lets pixel-material columns and other chains load and eventually break a rod without allocating a second full-grid buffer. Four-or-more-cell material columns reuse loads until their active-chunk revision changes; empty and shallow columns bypass revision lookup. Revision tracking and its buffers are opt-in, and the Rigid JavaScript and CSS are loaded only by ?run=rigid.

• src/: physics contracts, scalar oracles, Wasm SIMD kernels, Atomics transport, and tests
• web/: interactive lab, Worker and WebGPU adapters, and browser checks
• benchmarks/: recorded reproducible measurements
• tools/: browser benchmark drivers
• RESEARCH.md: implementation notes, tradeoffs, and measured boundaries

just check
just bench-browser
just bench-block-webgpu-events
just bench-reaction-webgpu-events
just check-webgpu

MIT