Making an IK-FK switcher

When creating rigs, we often face situations where we need to alter between two states or properties. The most iconic case is to alter from Inverse Kinematics (IK) to Forward Kinematics (FK) back and forth for a limb.

Forward Kinematics is the default state of regular chains of bones. When you move, rotate, or scale a bone in FK mode, all of its children bones inherit the same transformation. Therefore, we can say that the movement of a chain of bones in FK is driven by its base bone. It is often used for arm controllers when the character does not have its hands on a fixed position (such as doing push-ups).

Inverse Kinematics, on the other hand (no pun intended), works the opposite way: the movement of a chain of bones ...

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