Quick answer: Before flipping FK↔IK, copy the current rest pose to the target system. Use Match-FK-to-IK or Match-IK-to-FK nodes for seamless transition.
An animator switches the hand rig from IK (grabbing a sword) to FK (free pose). The hand snaps to a different position momentarily. The two systems have divergent rest poses.
Match Before Switch
Control Rig graph: when FK alpha rises from 0:
- Match FK To IK: copies the IK chain’s current pose to FK controls.
- Then ramp FK alpha to 1, IK alpha to 0.
FK starts where IK ended — no snap.
Blend Alpha Smoothly
FK_alpha = Lerp(FK_alpha, target, DeltaTime * 5.0)Even with matching, an instant swap looks abrupt. Smooth over 0.2s feels natural.
Match-FK-to-IK Node
Built-in Control Rig node. Inputs: FK control names, IK chain. On execute, sets FK controls to match IK pose. Run once at the moment of switch.
Snapshot Approach
Alternative: snapshot bone transforms before switch; apply post-switch to the new system. Manual but flexible for custom rigs.
Verifying
Toggle FK/IK in animator UI. Hand stays in place at transition, then animator controls take over. No pose jump.
“FK/IK switch is a continuity problem. Match the target before swap, blend smoothly.”
For combat animations with frequent IK switches (weapon hand on/off), wrap match-and-blend in a function library Control Rig — reuse across rigs.