Foot IK
Planting feet on uneven ground
Also known as: Foot placement IK · Foot IK Unreal · Foot IK Unity · Terrain foot adjustment · Feet on slopes · IK feet
Definition
Foot IK, or foot placement, adjusts a character's feet at runtime so they sit correctly on uneven ground, slopes and stairs, instead of floating or sinking through the surface. The engine casts rays down from each foot to find the ground, then uses inverse kinematics to bend the legs and lower the hips so that both feet touch. It also helps lock planted feet in place to prevent sliding. It is a standard feature of third-person character controllers in Unreal Engine, Unity and other engines.
In production
Make sure the skeleton has clean IK bones or can use a two-bone IK solver, and set the foot offsets for the sole and the ankle. Blend it with the animation, so it is strongest when the foot is planted and weaker in the air. Check the character on slopes and stairs, and keep limits so legs do not over-stretch. In Unreal Engine, Control Rig and the Foot Placement node help, and in Unity, the Animation Rigging package.
Tools that use Foot IK
See also
IK / FK
Inverse vs Forward Kinematics
Foot Sliding in Game Animation
Feet glide over the ground while walking
Control Rig
Unreal Engine node-based rigging and animation
Procedural Animation
Motion generated by rules and physics instead of keyframes
Skeleton
Hierarchical bone structure for animation
Root Motion
Movement driven by the animation, not the controller