Reactive materials

If you build your own terrain, prop, or foliage materials and want them to receive snow, rain, and wind from the sky system, use the included Material Functions. They read from the simulation’s published values (snow amount, wet amount, wind direction and speed) and inject the right effects without making you rewire your shader graph.

The material functions

Material Function	Use it on	What it does
MF_Snow	Any opaque surface (terrain, props)	Layers snow on horizontal-facing parts of the surface. Drives intensity from the sky’s simulated SnowAmount.
MF_SnowandRain	Same as above, when you also want wet/puddle effects	Combined snow plus wet-surface (puddles, ripples, drips, splash flipbooks).
MF_GrassWind	Grass blade materials, in WorldPositionOffset	Procedural sway. Driven by the system’s wind direction and speed. No inputs, just plug it in.
MF_BushWind	Bush/tree materials, in WorldPositionOffset	Higher-quality wind for larger foliage. Has an AdditionalWPO input so you can chain other deformations (player-crush, hit reactions).
MF_2DClouds	Sky-dome / horizon cloud overlays	Cheap horizon clouds at a configurable altitude.

Adding snow to a material

1. Open the material in your project.
2. In the Details panel, set Use Material Attributes = true.
3. Build your normal material as a Material Attributes bundle (everything goes through MakeMaterialAttributes).
4. Route that bundle into MF_Snow (or MF_SnowandRain).
5. Connect the function’s output to the material’s Material Attributes output pin.

Snow now appears automatically on horizontal faces whenever the sky says it is snowing. No per-material configuration needed. You can override snow textures, tiling, and color via the function’s exposed parameters.

Caution

Snow only accumulates on surfaces with an upward-facing normal. Vertical walls do not get snow on them; this is correct behavior. If your “wall” is actually a sloped surface and you expected snow, check the surface normal in Mesh Editor.

Adding wind to foliage

MF_GrassWind and MF_BushWind both go into the World Position Offset pin of your material:

1. Open the foliage material.
2. Find the World Position Offset pin on the material output.
3. Plug MF_GrassWind (for grass blades) or MF_BushWind (for bushes/trees) into that pin.
4. For MF_BushWind, optionally chain other WPO deformations through the AdditionalWPO input.

Wind direction and speed are read from the system automatically. The strength and frequency follow the simulated wind speed, so calm days are gentle and windy days lash.

Adding 2D horizon clouds

MF_2DClouds is for sky-dome cloud overlays, useful when you want cheap horizon clouds layered on top of (or instead of) the volumetric system. Drop it into a sky-dome material and configure the altitude parameter to taste.

Where to next

• Material functions reference: every exposed parameter on each function
• Weather states: what SnowAmount actually depends on
• Troubleshooting custom materials