This is effectively a C-port of Nathan Vegdahl's "No Twist" TrackTo PyConstraint, and has been added as a separate type of constraint to be consistent with the existing constraints (Locked Track, and Track To).
In general, this works considerably better than the existing "Track To" constraint, since it works by determining the smallest rotation necessary to get the current orientation of the owner to an orientation which would be tracking the target. It is also a much more straightforward approach than the weird old method the old Track To uses.
I've made a few tweaks to the code to deal with the (hopefully rare) cases where the target and the constrained are coincident. These don't appear to cause too much trouble in general.
TODO:
- Probably the naming of the constraints will change, to better convey their purposes. Naming suggestions welcome.
This commit implements more of the CopyPose capabilities in
Blender. It is now possible to select which axis will be
constrained in position and orientation to obtain
interesting effects. Another option selects if the axis
are relative to the end effector or to the target.
Unlocking a position axis means that the coordinate along
this axis is not constrained and can take any value.
Unlocking the Y axis of the End Effector produces an
'aiming' effect: the end effector is oriented towards
the target but without stretching.
Unlocking a rotation axis means that the end effector can
freely rotation along that axis. Unlocking the Y axis
produces a 'tangent' effect: the end effector aligns with
the Y axis of the target but can rotate along that axis.
A 'floor' effect is possible if the position Z axis of the
target is unlocked. More effects are possible an can be
combined.
