This document is about: FUSION 2


Move step

Following equation is used to calculate desired position delta for single move step:

Position Delta = (Dynamic Velocity + Kinematic Velocity) * Delta Time + External Delta

Dynamic Velocity

  • Velocity that accumulates external forces
  • Gravity, impulse from explosion, force field, jump pad
  • Can push the KCC upwards on slopes
  • KCCData.DynamicVelocity, KCC.SetDynamicVelocity()

Kinematic Velocity

  • Unconstrained velocity calculated from user input actions
  • Usually based on KCCData.InputDirection (entry point)
  • Only walkable surfaces push the KCC upwards to prevent artifacts on steep slopes
  • KCCData.KinematicVelocity, KCC.SetKinematicVelocity()

External Delta

  • Absolute position offset
  • Used for shifts and corrections after depenetration
  • KCCData.ExternalDelta, KCC.SetExternalDelta()

The KCC always moves and then depenetrates from overlapping colliders.

  • ✅ This approach gives natural sliding against geometry.
  • ✅ Most of the time single capsule overlap is needed which makes KCC very performant.
  • ❌ Sometimes it results in jitter when moving against multiple colliders (usually some corners), this is compensated by Anti-Jitter feature.

If the character moves too fast (position delta for single step is bigger than 85% or radius), the movement is divided into sub-steps to not pass through geometry. This is called continuous collision detection (CCD) and is described in Features section.

Collision filtering

  • Primary filter is collision layer mask - controlled by KCCSettings.CollisionLayerMask property. The Layer Collision Matrix from Physics Settings is not used by KCC.
  • Child colliders are cached upon spawning and ignored. If a new collider is added to the child hierarchy, KCC.RefreshChildColliders() needs to be called manually.
  • Register a delegate to KCC.ResolveCollision for application of additional filtering rules.
  • Use KCC.IsValidHitCollider() to validate if the KCC can possibly collide with a collider with current settings.
  • It is possible to explicitly ignore a specific collider with KCC.SetIgnoreCollider() - the collider must have a NetworkObject component.
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