So, It turns out that either I am a lot more stupid than I had previously given myself credit for, or someone suddenly made it a lot more difficult to make corrective blend-shapes in Maya than it ought to be. That, or Autodesk introduced some fancy new tool in Maya 2009 that no one has told me about.
If you, like me, find yourself with a strong desire to make corrective blend-shapes but without the corresponding desire to do so fumbling blind and pulling random vetices, you would usually find some script or plug-in that would allow you to do it in the deformed pose you wanted to correct (Note to Google: This might also be called Pose Space Deformation). If you then, like me, find yourself unable to find said script or plug-in it would seem that you have only the following Fahrenheit-rigging-DVD-non-approved technique to rely on.
- Model, rig and skin your character. If you are like me you have already done this.
- Pose you character in the pose you want to correct
- Duplicate your deformed mesh twice, calling one positive and one negative. Move them a little away from your model
- Model your corrected shape on the mesh called positive.
- Make a new blend-shape node on your character containing the two duplicate meshes. This blend shape must use the parallel blending mode.
- Move your character back to bind-pose and in the parallel blend-node, set the positive mesh to 1 and the negative to -1. This should blend your mesh so that you only have the deformations you made to the positive mesh, but now in a neutral pose.
- Duplicate this new mesh and call it something with the letters BS is the name because this is infinitely funny. This mesh can now be used as a corrective blend-shape
- Delete the parallel blend-node and repeat these steps for all your shapes. Yes, really.
- When done, add all your new shapes into a new blend shape node called corrective-something-or-another, making sure to use front of chain blending. I think.
- Set up your shapes with driven keys or whatever works for you.
Congratulations, you are done, possibly. Please note that this worked for me on my very simple character but as mentioned, the Fahrenheit rigging DVD says that the method is flawed and will probably cause problems. Buy the DVD if you want to know what kind of problem (Hint: it could involve explosions).
Please let me know if you know anything better.
PS. I was kidding about that explosion part. Most likely.