Guides

Snow

Snow has two halves. Flakes fall in a box around the camera, and snow cover builds up on your patched materials over time. The two run on separate dials, so a settled blanket can sit under a clear sky.

Snow starting on a dry square. set({ snow: 0.9, … }) starts the flakes, and cover builds on the roofs, benches and cobbles. Accumulation is sped up 4× here with weather.wetness.rate = 4.

#Falling snow

weather.set({ snow: 0.55 });          // calm snowfall
weather.set({ snow: 1, wind: 1 });    // driving snow
weather.loadPreset('blizzard');

snow (0–1) scales the flakes drawn, up to the tier's count: 9k on low to 42k on ultra. The flakes are swaying billboards in a 34 × 22 × 34 m box around the camera. In strong wind they stretch along their apparent motion, and now and then a tumbling flake glints. Like rain, they're culled under occluders.

Snow also thickens the fog (density + snow × 0.012, and a taller fog layer) and raises state.cloud to at least snow × 0.8.

weather.snow.flakeSize = 0.03;   // flake radius in metres (default 0.022)

`snowfall`: calm snow over a settled blanket

`blizzard`: gale-force wind and white-out fog

#Snow cover

Snow cover lives in weather.wetness (the SurfaceWeather) next to wetness. It is 0–1 and changes every frame:

Effect	Rate per second at full strength
Snowfall covers	`+0.03 × snow`
Rain melts	`−0.05 × rain × cover`
Daylight melts, only while it isn't snowing	`−0.003 × daylight`

Multiply the rates with weather.wetness.rate (default 1). To set cover directly:

weather.set({ snowCover: 0.8 });               // ease there over ~4.5 s, then accumulate naturally
weather.set({ snowCover: 1 }, { instant: true });
weather.wetness.force(null, 0.5, 2);           // ease to 0.5 over 2 s, wetness untouched

Presets carry a snowCover too: snowfall eases to 0.8 and blizzard to 1.

#Where it settles

Every patched material collects snow on up-facing faces:

Coverage uses the true face normal, so pitched roofs are covered even when the mesh has smooth vertex normals. The edge is broken up with noise.
{ ground: true } materials get the full blanket.
Anything under an occluder stays clear, like the ground under the well roof or a bench.
Covered surfaces are shaded with the face normal, glint in the sun (shadow-aware), and turn cool blue in shade.
Snow cover also counts as slight wetness (max(wetness, cover × 0.15)) and hides puddles.

NatureGL Weather — `snowfall` in the original page and in the package. The package covers the roof slopes, keeps the ground under the well roof and the benches dry, and adds glints.

weatherpro.html — `snowfall` in the original page and in the package. The package covers the roof slopes, keeps the ground under the well roof and the benches dry, and adds glints.

#Rain on snow

Rain on a snow blanket melts it at 0.05 × rain × cover per second, and splashes fade out as cover builds; above 90 % cover they're hidden. Going from snowfall to downpour gives you a thaw, not an instant switch.

#Using SnowSystem on its own

import { SnowSystem } from 'naturegl-weather';

const snow = new SnowSystem({ scene });   // maxFlakes 42000
snow.intensity = 0.6;
// per frame: snow.update(dt, camera);

Standalone flakes have no occlusion map and no wind, and there is no snow cover. Cover needs SurfaceWeather and the patched materials, which the facade wires up for you.