A fully procedural, physically based campfire in WebGPU. Everything you see and hear is computed: no textures, no images, no sound samples.

Built with Claude Code (Claude Opus 5.5).

• Simulation (src/sim.js): a 3D low-Mach combustion solver on the GPU (WebGPU compute). MacCormack advection, mixing-limited burning of pyrolysis gas with air, gas expansion as a divergence source, soot that forms after ~20–60 ms of gas age (which gives the blue flame roots) and burns out at the tips, soot radiative cooling, McCaffrey-calibrated buoyancy, vorticity confinement, rising curl-noise turbulence, and a multigrid pressure solver with open (entraining) boundaries. Heat release is ~50–60 kW, like a real campfire, and the flames puff at roughly 1.5/√D Hz because the units are real (metres, seconds, g). For the cinematic, pyrolysis is anchored to separate spots on the logs (distinct tongues with dark gaps), and hot-gas viscosity plus age-gated forcing keep the flame base laminar so tongues only wrinkle and break up towards the tips.
• Rendering (src/renderer.js, src/shaders/scene.js): a volumetric ray-marcher where flames emit Kirchhoff soot radiance κ·B(T) from a Planck spectrum integrated against the tabulated CIE 1931 observer, with lit smoke, sub-voxel curl-warp detail, an SDF scene (charred logs with glowing alligator cracks, coal bed, fire-ring stones, ground) lit by lights extracted from the flame volume itself, burning spark particles with energy-conserving motion-blurred streaks, heat haze, bloom, chromatic aberration, vignetting, grain and a camera-like per-channel tone curve calibrated against measured photos of real fire (research/visual_reference.md, tools/fire_metrics.py).
• Sound (src/audio/): procedural campfire audio (roar, breath, hiss, clustered crackles, resin pops, log shifts, embers, gusts, outdoor reverb), coupled to the simulation's light output and synced to the sparks.

WebGPU is required (Chrome/Edge 113+).

node tools/server.mjs 8787

Open http://localhost:8787/ and click to light the fire. Drag to orbit, wheel to zoom, S stoke, P pop, G gust, H hide UI, F fullscreen. Quality presets: ?q=low|med|high.

node tools/render_final.mjs

One command for the final 20 s vertical video (1080×1920, 30 fps): it renders the timeline (src/timeline.js: six shots, fire intensity, pops, log shift, gust) on the GPU with true motion blur (90° shutter, sub-frame accumulation) and thin-lens depth of field, then builds the soundtrack from the per-frame light output and the same event list, masters it to −14 LUFS / −1 dBTP and muxes out/video/final_final.mp4. The final flame and lens settings are in FINAL at the top of tools/render_final.mjs.

• --preview: 540×960 quick end-to-end check (picture + sound).
• About 3 h on an integrated GPU; on a cloud GPU (RTX 4090) roughly 15–25 min — see tools/runpod/README.md.
• --q cine: finer 5.4 mm simulation grid for a large GPU (not yet look-tested; compare with hero first).

The lower-level tools are tools/render_video.mjs (picture only, any settings) and tools/finish_video.mjs (soundtrack + mux for an existing render).

• tools/shot.mjs — headless deterministic stills, profiling, field statistics and photo metrics.
• tools/lens_test.mjs — A/B renders of chosen timeline moments with different sim, lens and render settings (fast-forwards the simulation without rendering); tools/compare.py builds side-by-side strips.
• tools/fire_metrics.py — scores a render against statistics measured on real fire photographs.
• tools/calib_tonemap.mjs — checks the tone curve against the measured camera "fire ramp".
• tools/ui_test.mjs — smoke test of the interactive viewer.
• research/ — physics, rendering, audio, visual-reference and WebGPU notes the implementation is based on.