Persona

Rain that actually falls through the stage. Drops are quads stretched along their own velocity — fall speed plus wind — so the streak is the motion blur a camera shutter would leave. The moment one hits a surface it freezes there and throws a brief expanding splash ring, then recycles to the top

It shares its GPU simulation system with snow, and like snow it is scene geometry rather than a stage in the post chain

Controls

×1 is a little over five metres per second, slightly slower than real rain — any faster and a streak crosses the frame in one tick as a nearly invisible line

Wind Steers the Streaks

Wind does more than blow the rain sideways. Streaks stretch along the combined fall-plus-wind velocity, so as wind rises the streaks tilt with it and the whole downpour reads as slanting across the stage

Wind is metres per second and is independent of the Speed multiplier — Speed only accelerates the fall. For a storm, push wind past 4, lengthen Drop Length and pull Opacity down a little; what you get is a dense sheet cutting across the frame

Drops wrap around the volume surrounding the stage, so no amount of wind can drain it

Splashes

Drops hit a top-down height map that sees everything on the stage — the avatar, props, and the implied ground underfoot. On contact the drop stops, and a splash ring spreads flat across that surface for about a third of a second before it fades

The splash lies flat on the surface it hit rather than always facing the camera, so from a low angle a splash on top of the head is foreshortened by perspective, exactly as it would be if it were really there

At Splashes 0 a drop recycles the instant it touches a surface — no ring, and none of its draw cost

Rendering in the Scene

Like snow, rain is real geometry in the scene:

• Lights do not illuminate it — streaks are self-lit transmissive highlights rather than lit bodies, so rain stays visible in the darkest scene
• Depth of field blurs it by its actual distance from the camera
• The whole look stack treats it like anything else, because it is already in the frame before those stages run
• Whether a drop is in front of or behind the avatar depends on where it happens to be falling

Cost

Rain does not occupy the post chain, so running it does not add a fullscreen pass the way the other effects do. Its cost is elsewhere: one compute dispatch per frame plus a height-map render every other frame — shared with snow, so enabling both does not duplicate height-map rendering

Amount is the main performance control. Buffers allocate for the maximum once, so moving it rebuilds nothing — but simulating more drops takes longer

Rain fades in and out over about 0.4 seconds when toggled, rather than appearing or vanishing outright