Understanding IK and FK

Before we move on to creating our own IK system, we should get a grasp of what IK and FK are. If you have experience in animation then you likely already know this. If you do not know the difference or need a refresher, the following subsections offer detailed explanations of both IK and FK.

Forward Kinematics

Rotating every bone one at a time into a pose is known as Forward Kinematics (FK).

In an FK chain, each successive bone inherits the rotation of the previous bone and is not affected by bones further up the chain. While it may feel like a very rigid system, it’s surprisingly the most effective way for animators to produce large sweeping arcs and precise movements. Its downside is that it requires an immense amount of effort and time to work with, so much so that it’s the much less frequently used of the two modes.

You may recognize this pose method because it’s what you have been using throughout the book to pose any of...