Alpha Piscium’s clouds are fully volumetric, rendered using the Nubis technique developed by Guerrilla Games for Horizon Zero Dawn. Each cloud is a density field built from layered noise functions — base Perlin-Worley noise for the large-scale cloud shape, curl noise for turbulent internal structure, billowy noise for puffy cauliflower formations, and wispy noise for thin trailing edges. Lighting is evaluated per-sample using a deep shadow map approximation with multiple scattering estimation, giving cloud interiors their characteristic soft self-shadowing. Two independent cloud layers are available: a low cumulus layer for the characteristic puffy fair-weather and storm clouds, and a high cirrus layer for the thin wispy ice-crystal clouds found near the tropopause.Documentation Index
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Global Cloud Lighting
Multiple Scattering and Ambient Light
Multiple Scattering and Ambient Light
Radius of the multiple scattering approximation, expressed as 2^x. Range: −5.0 to 0.0. Controls how far light is assumed to scatter laterally within the cloud volume. Higher values (closer to 0) produce brighter, more luminous cloud interiors and softer shadow gradients.
Ambient backscatter phase factor. Range: 0.0–1.0. Controls how strongly ambient sky light scatters back toward the camera from cloud interiors. Higher values brighten cloud bases and reduce the contrast between lit tops and shadowed undersides.
Cumulus (Low) Clouds
Enable and Rendering Quality
Enable and Rendering Quality
Enables the low cumulus cloud layer. These are the puffy, cauliflower-shaped clouds that form in the lower troposphere. Disable to remove low clouds entirely and improve performance.
Renders the low cloud layer at a reduced resolution and upscales the result. Options: 1.0×, 1.5×, 2.0×, 2.5×, 3.0×, 3.5×, 4.0×. Higher values improve performance at the cost of cloud detail. Default of 2.0× (half resolution) provides a good quality/performance balance.
Maximum number of frames blended for temporal cloud accumulation. Valid values: 4–128. Higher values produce smoother clouds with less noise but can introduce ghosting when the camera moves quickly.
Controls how quickly accumulated cloud samples gain confidence and sharpen over time. Range: 1.0–8.0. Higher values converge to a clean image faster but may show more initial noise after camera movement.
Strength of variance clipping used to prevent ghosting artifacts during camera movement. Range: 0.0–1.0. Higher values suppress more ghosting but can increase flickering; lower values allow more temporal reuse at the risk of cloud trails.
Minimum ray marching steps through the cloud volume, used when looking nearly straight up through relatively thin cloud sections. Valid values: 16–128. Higher values improve detail but reduce performance.
Maximum ray marching steps through the cloud volume, used when clouds are viewed near the horizon through thick cross-sections. Valid values: 32–256. Higher values improve the quality of dense cloud banks but reduce performance.
Cumulus Layer Geometry
Cumulus Layer Geometry
Base altitude where the cumulus cloud layer begins, in kilometers. Range: 0.0–8.0 km. Raising this value lifts clouds higher in the sky; very low values produce ground-level fog-like effects.
Vertical thickness of the cumulus cloud layer in kilometers. Range: 0.0–4.0 km. Thicker layers produce taller, more dramatic cloud formations; thinner layers create flatter, stratus-like clouds.
Density multiplier for the cumulus cloud layer. Range: 0.0–4.0×. Higher values produce denser, more opaque clouds. Very high values create dark storm clouds; lower values give wispy, translucent formations.
Fraction of the sky covered by cumulus clouds. Range: 0.0–1.0. A value of 0.0 produces a clear sky; 1.0 produces a fully overcast sky. The default of 0.5 gives a partly cloudy sky.
Cumulus Phase and Wind
Cumulus Phase and Wind
Ratio blending between isotropic and forward-scattering Henyey-Greenstein phase functions for cumulus cloud lighting. Range: 0.0–1.0. Higher values increase the bright silver lining and forward-scattering glow around cloud edges when lit from behind.
Enables animated cloud drift. When enabled, clouds move across the sky over time according to
SETTING_CLOUDS_CU_WIND_SPEED.Speed and direction of cloud movement. Range: −4.0 to 4.0. Positive values move clouds in the forward direction; negative values reverse movement. A value of 0.0 keeps clouds stationary.
Cumulus Shape Parameters
Cumulus Shape Parameters
These settings control the three-dimensional shape of individual cumulus clouds using procedural noise. All frequency values represent a 2^x offset applied to the base frequency.
Controls how pointed the upper portions of cloud structures appear. Range: 0.0–1.0. Higher values create sharper, more angular cloud towers.
Shape curvature of cloud tops. Valid values: 16–1024. Higher values create more angular, flatter tops; lower values round the tops into smooth domes.
Shape curvature of cloud bases. Valid values: 16–1024. Higher values create more angular flat bases characteristic of well-developed cumulus; lower values create fuzzy, undefined bases.
Frequency offset for the base cloud shape noise as 2^x offset. Range: −4.0 to 4.0. Higher values scale the noise up, producing smaller, more numerous cloud clumps; lower values produce larger, more spread-out formations.
Frequency offset for the large-scale curl noise distortion as 2^x offset. Range: −4.0 to 4.0. Higher values add finer curl turbulence to the overall cloud shape.
Frequency offset for the billowy (cauliflower) detail noise as 2^x offset. Range: −4.0 to 4.0. Higher values create smaller, more numerous billows across the cloud surface.
Strength of curl noise modulation on billowy formations as 2^x offset. Range: −4.0 to 4.0. Higher values make billows more turbulent and irregular.
Frequency offset for the wispy detail noise as 2^x offset. Range: −4.0 to 4.0. Higher values produce more and finer wispy tendrils trailing from cloud edges.
Curl modulation strength for wispy details as 2^x offset. Range: −4.0 to 4.0. Higher values create more dynamically swirling wisps.
Cirrus (High) Clouds
Enable Cirrus Clouds
Enable Cirrus Clouds
Enables the high cirrus cloud layer. Cirrus clouds are thin, wispy ice-crystal formations that appear at high altitudes. They add atmosphere and visual depth to the sky without the heavy performance cost of the cumulus layer.
Cirrus Layer Geometry
Cirrus Layer Geometry
Altitude of the cirrus cloud layer in kilometers. Range: 6.0–14.0 km. Higher altitudes produce thinner, more ethereal wisps characteristic of real cirrus clouds in the upper troposphere.
Density multiplier for the cirrus layer. Range: 0.0–4.0×. Higher values make cirrus clouds more visible and opaque; lower values create near-invisible, very fine wisps.
Fraction of the upper sky covered by cirrus clouds. Range: 0.0–1.0. Default of 0.4 gives a light covering that adds visual interest without dominating the sky.
Blend between isotropic and forward-scattering phase functions for cirrus lighting. Range: 0.0–1.0. Higher values increase the characteristic bright halo and iridescent glow that cirrus clouds exhibit when the sun shines through them.
Cirrus Shape Parameters
Cirrus Shape Parameters
Frequency offset for the billowy detail noise in the cirrus layer as 2^x offset. Range: −4.0 to 4.0. Higher values produce smaller, more tightly packed billowy textures within cirrus sheets.
Curl modulation strength for cirrus billowy details as 2^x offset. Range: −4.0 to 4.0. Higher values create more turbulent, swirling internal texture within cirrus formations.