Before the solving step, goals must be converted to an IK/FK state so they can be used by the solver to output a skeleton state.
Converting goals to an IK/FK state is straightforward. The IK state uses both the goals' rotation and translation and the FK state uses only the goals' extracted rotation. FK and IK effectors that don't have corresponding goals (because no markers were assigned to corresponding bones) simply take values from default stance pose.
Reaches can be adjusted to reach IK goals or keep the FK ones. When reaching IK translation, rotations up the hierarchy might be changed so that the translation is reached. For this reason, IK effectors have the same rotation as FK effectors so that if the rotation is kept, you can also reach this rotation. For example, if translation is set to be reached on the IK wrist effector, solving can change the extracted rotation on the elbow so that the wrist reaches the right position. If the elbow rotation (i.e. its angle) is important, reach can be set on the elbow rotation so that it is maintained during the solve (which might result in the shoulder getting pulled for example). This is why IK effectors have the same rotation as FK effectors.
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