Forces & collisions
Push a simulation around with force fields, and give it something to bump into with colliders.
A simulation on its own falls under gravity. Force fields shape how things move: wind, swirls, attraction, turbulence. Colliders give particles, cloth and bodies something solid to land on, slide along and pile up against. Both feed the same solver and stack together.
Force fields
The Force Field node makes a force to wire into a simulation. Pick a type.
Directional, a uniform push in one direction. Wind, or an extra gravity override.
Point, pulling toward or pushing away from a single point. An attractor or a repulsor.
Vortex, spinning everything around an axis. Tornadoes, whirlpools, swirling sparks.
Turbulence, procedural noise that jitters and churns. Drift, smoke wisps, organic chaos.
Drag, slowing things according to how fast they move. Air resistance, or thickening the feel of a fluid.
Each field has a falloff so its strength fades with distance: None, Linear, Quadratic or Smooth. Add several fields and they combine, so wind plus turbulence plus a point attractor all act at once.
Drag is the one field that reacts to velocity rather than position. Use it when a sim feels floaty, or when particles should settle instead of coasting forever.
Up to 16 force fields can act at once, of which up to 8 may be Drag fields. Gravity is itself a built-in Directional force and counts against that budget.
| Parameter | Type | Default | What it does |
|---|---|---|---|
force_type | String | "Directional" | Force type: Directional (wind), Point (attractor/repulsor), Vortex (rotational), Turbulence (noise), Drag (velocity damping). One of: Directional, Point, Vortex, Turbulence, Drag. |
direction_x | Number | 1 | Force direction X (Directional: wind direction, Vortex: rotation axis) |
direction_y | Number | 0 | Force direction Y |
direction_z | Number | 0 | Force direction Z |
strength | Number | 50 | Force magnitude (negative = invert direction for Point) |
position_x | Number | 0 | Force origin X (Point/Vortex center, spatial falloff origin) |
position_y | Number | 0 | Force origin Y |
position_z | Number | 0 | Force origin Z |
radius | Number | 0 | Influence radius (0 = global/infinite) |
falloff | String | "None" | Falloff curve within radius. One of: None, Linear, Quadratic, Smooth. |
noise_amplitude | Number | 0 | Noise amplitude (gustiness for Directional, full strength for Turbulence) |
noise_frequency | Number | 0.010 | Noise spatial frequency |
noise_speed | Number | 1 | Noise temporal speed |
Forces from a Volume
A Volume holding a 3D vector per cell can drive a simulation. Wire a vector Volume into the simulation's input and it acts as a spatially varying force, a baked wind map or a curl-noise field, which is the route to art-directed flow that changes from place to place. See Volumes for making Volumes.
Volume forces currently push particles, not 6-DOF rigid bodies. Per-Volume strength controls are not implemented yet, and defaults apply until they are.
Colliders
A collider is something a simulation cannot pass through. Add a Physics Collider node with a built-in shape, box, sphere, convex hull, or the mesh itself, and wire it into the simulation alongside the bodies. Cloth drapes over it, particles pile against it, rigid bodies bounce off it.
The simulation also has a built-in ground option, which covers the common case without a separate floor collider. Colliders carry friction, so surfaces run anywhere from ice to sandpaper. Anti-tunnelling is always on, so a fast-moving object will not shoot through a thin collider, and there is no setting for it.
Distance Field colliders
For collision against arbitrary shapes rather than the basic primitives, use a Distance Field as a collider. Wire a Distance Field Volume into the simulation's input and it becomes a static collision boundary following the exact contours of the shape.
The collider must be a true Distance Field, one that knows how far every point is from a surface. A plain density or fog Volume has no surface to collide against. If you only have a density Volume, extract a Distance Field from its surface first. See Distance fields & volumes.
Collision layers
Collision layers control which groups of objects interact. Put character bodies on one layer and debris on another and the debris collides with the world while passing through the character, or any other combination.