Foot IK
Adjusts the leg bones with inverse kinematics at runtime so feet plant on the ground instead of floating above or sinking into slopes and stairs.
A walk cycle is recorded against a flat floor, so the moment the ground tilts it no longer matches. Foot IK corrects that per frame: a ray is cast downward under each foot, the hit point becomes the new target, and a two-bone IK solver bends the thigh and shin so the foot reaches it. The foot is then rolled to lie flush with the surface's slope.
To keep the leg from over-extending on an uphill, the pelvis is usually lowered to the lowest-placed foot. The effect is most visible on stairs and rough terrain, where the character would otherwise either hover or dig its toes in — a standard feature in modern engines like Unreal and Unity.