Precipitation Surfaces

Treat weather as a coupled event, particle, and surface-response system. Do not add rain or snow particles that are visually disconnected from the ground.

This skill contains exemplary examples and assets beyond descriptive guidance, they're worth studying, referencing, or even copying. Use them sufficiently when relevant and do NOT blindly skip them.

Build order

weather envelope
  -> falling precipitation volume
  -> world/object surface mask
  -> displaced or optical surface response
  -> impact residue and splashes
  -> shared lighting/post presentation

Read references/precipitation-surface-systems.md for snow accumulation, object capping, wrapped precipitation volumes, wet puddle masks, procedural ripple normals, splash placement, debug outputs, and licensing boundaries.

Read the snow accumulation implementation for camera-wrapped snowfall, shared wind/time uniforms, world-space snow masks, single-source snow height and normals, model snow capping, and optional ice surface composition.

Read the wet puddle rain implementation for rain-progress wetness, asphalt puddle masks, procedural ripple normals, instanced rain streaks, upward-surface splash sampling, and flipbook splashes. This example includes GPL-licensed source material; preserve its license boundary when copying or publishing it.

Required controls

• precipitation density and speed;
• wind direction and strength;
• shared weather progress or coverage;
• wetness, snow, or puddle mask threshold and softness;
• ripple or drift normal strength;
• surface roughness response;
• particle/splash opacity;
• debug modes for masks, normals, particles, and event progress.

Failure conditions

• falling precipitation ignores the wind or timing used by surface response;
• snow height and snow normals come from different fields;
• model snow sticks to vertical faces without an upward-facing filter;
• puddles only lower roughness without a mask, normal response, or ripples;
• splashes appear on downward or hidden faces;
• rain streaks allocate per drop or fail to wrap around the camera;
• temporal wetness is faked with unrelated time noise;
• the license boundary for GPL-derived rain code is removed or obscured.

Routing boundary

Use $threejs-water-optics for bounded pool simulation, caustics, Fresnel, refraction, and Beer-Lambert water volumes. Use $threejs-procedural-vfx for general sparks, plasma, trails, and non-weather particles. Use $threejs-temporal-surfaces for screen-space touch history or frost clearing. This skill owns precipitation events and the surfaces they visibly alter.