Firmament - Unity 6 URP Volumetric Sky, Grass & Moss: Day-Night Cycle, Weather, Hills

FirmamentRig drives the directional sun and moon, the ambient light, the fog, the sky material and a sky reflection probe from a single clock, using real solar geometry: set the latitude and the day of the year and the sun rises where it would, at the height it would. Every light in the scene follows the sky, so dusk is lit like dusk. The reflection probe captures the sky alone, a face per frame, so reflections follow the time of day without redrawing the scene.

Six presets come with it as sky materials — clear morning, fair weather, broken cloud, overcast, storm and alien dusk — each a starting point: duplicate one and change any colour, because nothing in them is painted.

One value, 0 to 1. It moves coverage, density, absorption, cloud-top height and edge erosion together, because those five move together in the real sky — asking you to keep them consistent by hand would be asking you to do the shader's job.

Erosion is tied to it deliberately: billowed, cauliflower edges belong to fair-weather cumulus. A storm deck is one solid sheet, and applying cumulus erosion to it punches holes that show blue sky through an overcast.

FirmamentGrass draws a field of wind-animated blades as instanced patches that wrap around the camera, so the field never runs out. Point it at the rig and the wind comes off the same weather value as the clouds — turn the dial toward a storm and the cloud thickens, the sun dims and the field starts to move, because in the real world those are not three separate settings.

It plants on three kinds of ground: flat, Firmament's own hills, or yours — a Unity Terrain read straight from its heightmap, or a single-channel texture with the world rectangle and height range it covers, outside which no blade is drawn. Density, view distance, dryness and blade height are on the component.

FirmamentTerrain is endless: the land is computed, not stored, so it goes on to the horizon in every direction with nothing to import. Pick Flat, Rolling or Hilly, or set the height, scale and roughness yourself. A flatten pad seats a building or the stone circle on level ground. A collision patch follows the player or the camera, and HeightAt and NormalAt return the same ground the terrain draws, for placing your own objects.

FirmamentMoss points at a model and grows moss over every mesh under it, where moss would grow: on tops and ledges where rain collects, on the side of a stone the sun seldom reaches, up the damp foot of every stone and in the hollows. Sunny faces and sharp edges stay bare. Nothing is painted and nothing is authored per model — no textures, no UVs, no import step. One Growth value takes a model from bare stone to overgrown; animate it and a ruin greens over in front of the player.

Point it at the rig and the moss soaks through to a deep green under rain cloud and dries out slowly after, and the shaded side follows the latitude. Near the camera it is drawn as cushions with real depth that break the outline of an edge; further off, flat on the surface. It is made for opaque URP Lit materials and carries their base colour, base map and smoothness across.

The monument in the demo comes with the pack, under the same licence as everything else. 63 stones, about 75k triangles, one mesh, no textures: the weathering is baked into vertex colours, drawn by the vertex-colour Lit shader that comes with it, so damp dark bases, rain-pale tops and lichen patches cost nothing to ship. It follows the real plan and the real ruin — a surviving run of lintels, two broken trilithons, fallen stones, an altar stone and a heel stone.

The landscape kit is 20 boulders, outcrops, walls and dead timber in the same stone, as FBX; the demo scatters most of them round the circle.

• FirmamentCloudFeature marches the volumetric sky's clouds at a fraction of the camera's resolution — half by default, a quarter of the pixels — before the skybox draws, so the atmosphere, the sun, the moon and the stars stay sharp. Clouds are soft, so it looks the same.
• FirmamentFogFeature adds distance and height fog once the opaque scene and the sky have drawn, in the colour the rig gives it.
• An ACES filmic tonemap, as a renderer feature of its own.
• Firmament/Sky Flat — domain-warped 2D clouds, very cheap. Convincing from the ground; it is a painted ceiling if you fly through it.

Firmament → Configure Project switches the project to Linear colour and HDR, adds the three features to the Firmament renderer, and makes the Firmament URP asset the project's active pipeline. For the browser, webSkyQuality on the rig lowers the cloud and light steps; the demo above uses it.

Everything is procedural — the cloud shapes, the atmosphere, the stars, the moon. That is why there is nothing to import, and why you can change any colour without repainting anything.

• The weather dial is the sky's: cloud, light and wind. There is no rain or snow.
• URP only. Not the Built-in pipeline, not HDRP.
• The moss is made for opaque URP Lit materials. It carries their base colour, base map and smoothness, not normal maps or emission, and it grows on mesh renderers, not skinned meshes.
• The torches and fireflies are part of the demo scene. They are there to show the night, and you are free to keep them.
• The flat sky is a painted ceiling, not a volume: fly into it and it stays overhead.
• It is tested in the Unity 6 editor on macOS and in the WebGL 2 build. Other build targets have not been tested.

The download

The licence

Use it in commercial and non-commercial projects, unlimited titles, no revenue cap. Modify it freely. Attribution appreciated, not required. You may not resell or redistribute the asset itself.

Full terms are in Assets/Firmament/LICENSE.txt and Assets/FirmamentMoss/LICENSE.txt.