Inverse Kinematics and Foot Locking

summary

Foot sliding occurs when the runtime velocity of a character's feet does not match the source animation data, typically during contact phases. To solve this, developers can use a combination of inverse kinematics (IK) to position the toe, inertialization for smooth runtime transitions between locked and unlocked states, and PBD-like constraints for offline processing. The core goal is to preserve the original animation's intent and velocity rather than strictly enforcing physical friction.

key points

1. A robust leg solver should use a two-bone IK system that softly clamps extensions to avoid hyper-extension and uses the knee's side vector for stability without needing a pole vector.
2. Runtime foot locking is achieved by tracking a static contact location on the floor and using cubic inertialization to smoothly transition the toe target between the animation source and the locked position.
3. Offline foot sliding removal can be formulated as a set of constraints on pelvis and toe particles, which are iteratively solved to distribute adjustments across the entire animation clip for higher quality results.

who should read it

Game developers and animation programmers who want to implement realistic foot-ground contact and reduce visual artifacts in character locomotion.

discussion positive