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Brush Physics is a PhysX Painter tool that spawns instances of the selected prototypes above the surface and lets them fall and settle using physics simulation. Each click or drag stroke scatters objects according to your Scatter settings, spawns them at a raised height above the hit point, then runs the physics simulator until they come to rest.
New to Brush Physics? Follow the step-by-step Brush Physics — Getting Started tutorial first.

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Supported resource types

Brush Physics supports:

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How it works

  1. You click or drag in the scene view. The tool casts a ray downward at each point where the mouse moves.
  2. For each hit, the Scatter system generates sample positions within the brush area.
  3. Each sample is raycasted downward. On a valid hit, a random prototype is selected based on Success weights.
  4. The prototype is instantiated at the hit point offset upward by Position Offset Y, then dropped. Physics simulation runs immediately with acceleration mode enabled.
  5. When physics settles (or the per-object time limit is reached), the object is frozen in place.
  6. The Physics Effects force is applied to each spawned rigidbody at the moment of instantiation, which can give objects an initial push.

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Tool-level settings

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Brush Physics Tool Settings

  • Position Offset Y — how far above the surface hit point the object is spawned before falling. Default: 30. Increase this to give objects more fall distance; decrease it if objects are landing with too much velocity.

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Physics Effects

Controls the initial impulse applied to each spawned object at the moment of spawn. See Physics Effects Settings for all fields.

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Brush Settings

Controls the brush shape, size, and spacing between strokes. See Brush Settings.

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Prototype-level settings

Each prototype in the group has:
  • Success — controls the probability that a given prototype is chosen and that a specific sample point results in a placement.
  • Physics Transform Settings — transform components (rotation, scale) applied before the object is handed off to the physics simulator.

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Group-level settings

  • Spacing — the minimum cursor travel distance before a new stroke fires. Shared via the Brush Settings.
  • Scatter Settings — controls how sample points are distributed within the brush area (random, grid, Poisson disc).

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When to use Brush Physics

Brush Physics is best when you want to:
  • fill an area with objects that settle naturally onto uneven terrain;
  • create piles, debris fields, or loose scatter that looks physically plausible;
  • paint quickly across a large surface and let physics do the positioning work.

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Notes

  • The tool belongs to the PhysX Painter family.
  • Undo is registered after you release the mouse button, so a full drag stroke is undone in one step.
  • The physics simulator uses acceleration physics mode and ObjectTimeDisablePhysicsMode, which means each object is simulated for a time limit rather than globally.