A downhill mountain-bike game in Three.js, built with zero authored assets.
Every texture is generated from a seeded PRNG at boot, every mesh is built in code, all audio is
synthesised with WebAudio, and the rider is a procedurally-built skinned rig driven by inverse
kinematics from the physics state. There are no images, models, sound files or fonts in this
repository. The only runtime dependencies are three and postprocessing.
npm install
npm run dev # http://localhost:5178Query parameters: ?quality=low|medium|high|ultra, ?seed=<number>, ?debug.
| World | 3072 m square, 1537² heightfield, ~700 m of relief, hydraulic erosion, quadtree LOD |
| Trail | 2.7 km descent, 8 named phases, route-found down the fall line, carved into the terrain with banking solved from expected entry speed |
| Terrain material | 8 procedural surface layers in a texture array, triplanar projection, height-based splat blending, stochastic tile-break with explicit gradients |
| Sky | Tuned Preetham atmosphere, raymarched volumetric cloud deck, cloud shadows, height-based aerial perspective, PMREM environment |
| Vegetation | ~200k instances, three procedural conifer species, three LOD tiers with baked impostors, coherent gusting wind, coverage-preserving alpha mips |
| Physics | 240 Hz fixed step, per-wheel load transfer, slip-ratio/slip-angle tyre model, independent progressive fork and shock, rider lean pendulum with a grip-derived ceiling, pumping, air control, landing evaluation |
| Bike | Four-bar Horst link solved per frame by circle–circle intersection, 32-spoke 3-cross lacing, chain solved as a belt over four circles, 200 mm vented rotors |
| Post | HDR highlight roll-off, adaptive exposure with camera-cut detection, ACES, procedural grading LUT with a boot-time white-point assertion, N8AO, SMAA, bloom, motion blur |
| Game | Run state machine, 8 checkpoint splits, persisted PB, 30 Hz ghost replay, style scoring, crash/respawn, keyboard + gamepad with rumble |
Real frame at 1920×1080 — all seventeen systems ticking, bike descending, camera in chase:
| section | ms | fps |
|---|---|---|
| open alpine | 10.35 | 96.6 |
| jump line | 13.13 | 76.1 |
| dense forest | 15.29 | 65.4 |
| final sprint | 13.04 | 76.7 |
Physics, independently re-verified: terminal velocity 17.18 m/s on a 15% grade (identical at 30/60/144 Hz), static sag 29.4% fork / 26.7% shock, braking 8.37 m/s², pumping skill gap 3.56 m/s between best and worst phase, zero NaN and zero tunnelling across 300 s of random input at mixed 20–240 Hz.
Image telemetry across the 16-shot review set: 0.0% crushed pixels (L<6), 0.0% clipped (L>250).
This is not current-generation console quality and does not claim to be. An independent review panel placed it alongside Steep (2016, PS4-era) and Descenders (2019) — above both on terrain material, lighting and physics simulation, below them on character readability and art cohesion. As a browser renderer it is unusually complete; as a game it is not finished.
Known open items are tracked in qa/:
- The trail cannot yet be ridden end to end. The corner-berming pass runs in only 3 of the 8 course phases, so the tightest corners are built with roughly 15° of bank where they need 45°.
- The rider reads as a mannequin at close range — the IK solver is sound, the garment and hand geometry are not.
- Foliage is procedurally authored and reads as cards rather than photographic plates.
- There is no asset pipeline (no glTF/KTX2 import), which gates any authored art entering the project at all.
src/core/ engine, post-processing, shared context, RNG
src/world/ terrain, terrain material, trail, sky, vegetation, water
src/physics/ bike dynamics, terrain collision
src/entities/ bike model, rider
src/camera/ chase camera
src/game/ gameplay, input, particles
src/ui/ HUD, menus
src/audio/ synthesised audio
qa/ review harness, screenshots (gitignored), triage documents
CONTRACT.md module interface specification
ADDENDUM.md integration facts discovered during the build
CONTRACT.md is the authoritative interface spec: it was written before the modules and is what
allowed them to be built independently and still link up.
MIT