Skip to main content

Collision Setup

Set up collisions to prevent bones from penetrating through the body.

note

This page is a setup guide. For all properties and default values of each collision shape, see Collision Parameters.

Collision system overview

Examples of collision placement and the purpose of each shape (diagram labels are in Japanese).

Collision Types​

Sphere​

Suitable for spherical parts like head and shoulders.

Sphere collision example

Capsule​

Suitable for cylindrical parts like arms and legs.

Capsule collision example

Plane​

Used for flat surface restrictions like ground and walls.

Box​

Version Info

Added in v1.17.0

Box-shaped collision. Suitable for rectangular shapes like body and buildings.

UPROPERTY()
TArray<FBoxLimit> BoxLimits;

FBoxLimit Properties:

PropertyTypeDefaultDescription
DrivingBoneFBoneReference-Bone that collision follows
OffsetLocationFVector(0, 0, 0)Location offset from the Driving Bone
OffsetRotationFRotator(0, 0, 0)Rotation offset from the Driving Bone (range -360 to 360)
ExtentFVector(5, 5, 5)Box half-extents (size in each axis direction)
note

DrivingBone / OffsetLocation / OffsetRotation are common to all collision shapes (FCollisionLimitBase). FSphericalLimit adds Radius (default 5) and LimitType (Inner/Outer); FCapsuleLimit adds Radius (default 5) and Length (default 10).

Collision Generation from PhysicsAsset​

Version Info

Added in v1.17.0

You can auto-generate collision shapes from existing PhysicsAssets. Collision bodies defined in PhysicsAsset are converted to KawaiiPhysics collisions.

Usage​

  1. Select KawaiiPhysics node
  2. Set existing PhysicsAsset to Physics Asset property
  3. Collision shapes are automatically generated

Benefits​

  • Reuse existing PhysicsAssets
  • Reduces manual collision setup work
  • Consistent collision settings

Adding Collision​

  1. Select the KawaiiPhysics node
  2. Add elements to Spherical Limits / Capsule Limits / Box Limits / Planar Limits array
  3. Set Driving Bone (bone that collision follows)
  4. Adjust offset and size

Driving Bone​

Collision follows and moves with the Driving Bone.

upperarm_r (Driving Bone)
    ↓ Follows
[Capsule Collision] → Hair stops here

Inside vs Outside​

Inside (Inner Limit)​

Limits bones to inside the sphere.

  • Use case: Following head shape

Outside (Outer Limit)​

Limits bones to outside the sphere.

  • Use case: Preventing penetration into shoulders

Performance Considerations​

More collisions increase processing load.

tip
  • Use the minimum necessary collisions
  • Approximate complex shapes with multiple simple shapes

For more details, see Performance.