Guides

Clouds and weather

The clouds are a world-space slab at a real altitude, marched from wherever the camera is. A handful of weather parameters shape them, and every one of them eases, so the weather can change while you watch.

applyPreset('overcast') and then applyPreset('storm') on a running sky. Coverage, density, precipitation, the sun colour and the ambient light all ease together.

#Cloud forms

cloudForm picks the cloud's shape. The other parameters shape it further.

`cloudForm`	What it looks like	Presets
`cumulus`	Fair-weather puffs to full decks, depending on `humidity`	`clear`, `marine`, `overcast`, `storm`, `night`
`altocumulus`	Small mid-level puffs in rows: a mackerel sky	`altocumulus`, `sunset`
`towering`	Cumulus congestus: isolated cauliflower towers	`towering`, `golden`
`cirrus`	High fibrous ice cloud; the dome stays blue	`cirrus`
`noctilucent`	Electric-blue high cloud lit after sunset	`noctilucent`
`cumulonimbus`	One monumental cell anchored at (0, −9.5 km)	`cumulonimbus`

#The weather dials

All of these are 0–1 unless noted and ease when set through setParams or applyPreset.

Param	Default	Effect
`humidity`	`0.5`	Cloud cover and the amount of cirrus
`coverage`	`0`	Extra cover on top of humidity (−1 … 1)
`precipitation`	`0`	Dark bases, rain veils, gloom; lightning above `0.4`
`temperature`	`0.45`	Base altitude and vertical growth
`density`	`0.55`	Extinction: thin wisps to solid towers
`edge`	`0.58`	Erosion strength: soft edges to crisp edges
`clump`	`0.5`	Weather map: km-scale clumps and clearings
`wind`	`0.35`	Drift speed
`windDirection`	`293`	World azimuth the clouds drift toward (degrees)
`cirrus`	`1`	Cirrus multiplier (0 – 2)
`haze`	`0.14`	Aerosol: milkier sky, redder sunsets, hazier distance

// a building afternoon storm
sky.setParams({ humidity: 0.85, temperature: 0.7, precipitation: 0.55, wind: 0.6 });

The full list, including exposure and post-pass dials, is on Sky parameters.

#Rain and lightning

When precipitation rises past about 0.4, the deck darkens and rain veils hang under it. Lightning then flashes inside the cloud. sky.lightning reports the current flash (0 – 1.5), so you can flash your own lights with it. Set lightning: 0 to turn the flashes off.

storm: a squall line with rain veils and in-cloud lightning, and the low sun under the deck.

renderer.setAnimationLoop(() => {
  sky.update(dt);
  lampLight.intensity = base + sky.lightning * 40;   // your own light reacts to the flash
  renderer.render(scene, camera);
});

#Fly through them

The slab has a real base and top in metres (sky.cloudLayer). The camera can be under it, inside it or above it. The march adds near steps adaptively when you're inside.

#Static and dynamic rendering

const sky = await SkySystem.create({ renderer, scene, camera, cloudRenderingMode: 'static' });
sky.setCloudRenderingMode('dynamic');

dynamic (default): clouds drift and evolve, lightning flashes, and the shadow and environment maps refresh on their quality-tier interval.
static: evolution is frozen. The LUT, shadow and env maps only re-bake when a parameter or the time changes. Use it for product shots, architectural scenes, or anywhere GPU time is tight.

#Cloud shadows

The sky keeps a top-down transmittance map of the deck around the camera (±8 km by default, shadowExtent). Any built-in lit material can sample it:

sky.patchMaterial(terrain.material);   // Standard, Physical, Lambert, Phong, Toon

For your own shaders, see Lighting your scene.