(Just in case this might help someone doing morph targets) For mirroring characters when you can’t change vertex order, like when modeling morph targets, this is a great script. Old, but still works:
The mirror modifier will not allow you to create a good UV mapping before applying it, UV maps follow no rules as to how they are aligned regarding symmetry axes, so the modifier can’t really attempt to mirror a UV map.
For creating shape keys (the closest thing to morph targets in Blender) you can’t use it because you are working on a half model. When you hit the “Apply” button, a message appears saying that all keys, among other things, are going to be deleted.
Mirrors not only reflect half things so they look as they were one full thing, they can also reflect full things even if they are asymmetric:
The modifier also requires that all vertices along the seam are kept aligned. You can’t create an expression where seam vertices actually cross the symmetry plane. A good example is all the movement you can do with your mouth and tongue.
That is why there are some mirror scripts around. They will keep UV, vertex color and weight maps or vertex order.
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