version: "1.0.0" name: threejs-water-optics description: Build production analytic and bounded water in Three.js. Use for shared multi-wave displacement and normals, bounded RGBA heightfield pool simulation, local drops, object-driven ripples, differential-area caustics, ray-traced pool/water/sphere volume optics, derivative-filtered normal bands, analytic sky reflection, side-aware Fresnel, heuristic screen refraction, Beer-Lambert absorption, and crest foam.

Water Optics

Treat water as geometry motion, surface orientation, and a participating optical layer. A blue transparent material is not a water system.

For large stochastic seas driven by directional spectra and GPU FFTs, use $threejs-spectral-ocean instead.

Analytic surface build order

1. Define wave bands and evaluate displacement.
2. Derive the normal analytically from the same waves.
3. Choose displaced geometry or explicitly normal-only water.
4. Establish scene-color ownership for heuristic refraction.
5. Declare whether absorption uses true depth or a fallback path-length estimate.
6. Blend analytic reflection/refraction through side-aware Fresnel.
7. Derive foam and glints from the shared wave response.
8. Filter unresolved normal bands from derivatives.

Read references/water-surface-system.md for the exact five-wave displaced ocean, six-band normal-only water, optical hierarchy, and the limits that distinguish both from the spectral-ocean skill.

Read the analytic wave optics implementation for shared displacement/normals, derivative filtering, reflection, screen-space refraction, absorption, Fresnel, and crest-linked foam diagnostics.

Read the interactive pool volume implementation for bounded RGBA height/velocity/normal simulation, local drops, moving-sphere displacement suitable for draggable objects, differential-area caustics, and shadered pool/water/sphere ray tracing against the pool bounds and sphere.

Failure conditions

• normal texture motion does not agree with displaced crests;
• heuristic refraction can sample foreground objects but the limitation is undisclosed;
• fallback path length is presented as reconstructed scene thickness;
• bounded pool caustics are a decorative projection detached from simulated

height normals;

• micro-waves alias into sparkling noise;
• foam is a scrolling texture unrelated to the shared crest metric;
• Fresnel is replaced by constant opacity;
• reflection, refraction, and transparency are all added without energy control.

Routing boundary

Use $threejs-spectral-ocean for stochastic directional spectra, FFT cascades, Jacobian breaking, and persistent ocean foam. Use $threejs-precipitation-surfaces for rain-driven puddle wetness, ripple masks, and weather-coupled splashes on ground surfaces. This skill owns authored analytic waves, bounded heightfield simulation, ray-traced pool-volume optics, and bounded-water optics.

Source: Scott Sun, MIT. Adapted by LumosLab: example assets remain linked to pinned upstream source; skill instructions and references are bundled. See LICENSE.