Hey Kirk! Animator here, although I’m by no means an expert and I’m not involved with Horizon in any way so I have no concrete insight into the development of this animation flourish.

Inverse Kinematics (or IK as we call it) is indeed involved, but that isn’t what makes the animation special. IK is used all over the place in all CG animation on a daily basis so it’s very par for the course. Most often it’s used in running and walking animations because the foot has to be planted on the ground while the body moves above it. IK is also what’s behind that trick where a game character’s feet adjust to the slope of the terrain; the orientation of the foot is calculated based on the slope. I loved this when first spotting it in Ratchet and Uncharted back in 2007.

IK controls glitching out is actually what causes those clips on Highlight Reel where Witcher III and Skyrim characters walk with their feet way up off the ground; the height of the terrain in relation to the feet is being mis-calculated.



As for this trick, if I were to take a gander, I’d say that the pose of her feet is being automatically driven by where Aloi is oriented in relation to her mount. So for example, if she is facing 3:00 on the mount then she has her foot tucked over the mount’s back. All the poses are pre-determined based on her orientation, and rotating around blends between the various poses.

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Further reading: IK’s opposite in animation is FK, or Forward Kinematics. Where IK animation has the end joint driving the limb structure, like a puppet, with FK each joint is rotated individually, like an action figure. FK is useful when the character isn’t planting the limb on something, like standing on the ground or leaning on a wall with their arm, and is generally desirable because it’s the easiest way to have arcs (which is one of the twelve rules of animation).



Fun fact: The entirity of the original Toy Story was animated before IK was invented.

