Create post-skinning corrective shapes

Corrective shapes are blend shapes that you create in order to fix problems with the deformation on the base object. This is often a method used on a character's skin to fix specific deformation problems that you find when the character is animated. You can make the corrective shapes so that they're applied to the skin either before or after the skin deformer is evaluated. The shape deformation results and workflow are different for each method.

When you create a corrective shape on the skin that is evaluated after the skin deformer, it is done in consideration of how the skin deforms during animation. The post-skinning corrective shape can be based on either the skin's tangent space or a joint's transform values (position and rotation).

• Tangent Space target shapes use the space relative to the base object's surface to calculate the skin deformations. The local vertex frame is used to calculate the tangent space, not the object's UVs.
• Transform Space target shapes use the transform space defined by a selected skeleton joint to calculate the skin deformations.

Transform Space target shapes are generally faster to compute than Tangent Space, and any corrections you make to the shape are within the envelope area of the selected joint.

Tangent-space corrective shapes

To create a tangent-based post-skinning corrective shape

1. Go to a frame where the character's skin is deforming incorrectly, or move the character into a pose where you want to add a corrective shape.
2. Select the character's skin mesh.
3. Open the Shape Editor and choose Create > Blend Shape Deformer > .
4. In the Blend Shape Options, click the Advanced tab and select Post-deformation from the Deformation Order list.
5. Click the Create button to create the blend shape deformer on the skin mesh.
6. In the Shape Editor, either click the Add Target button or choose Create > Add Target > .
7. In the Add Blend Shape Target Options, select Tangent Space from the Type list to create a tangent-based target shape for this blend shape deformer. Click Apply and Close.

   A green target icon appears beside the target shape's name in the tree to indicate that it is tangent-space based.

8. The target shape's name is automatically the same as the name of the skin mesh, but you can change it: double-click the name or right-click it and choose Rename, then enter a new name.
9. Make sure that the target shape's Weight value is set to 1 for 100% influence for the corrective shape's effect, and click its Edit button if it's not already red. You're ready to edit the skin mesh.
10. Use Sculpting tools to deform the skin so that it's correct, or select the object components you want and use Transform tools to deform the skin - see Edit target shapes for more information.
11. Click the Edit button again when you're finished the shape to exit Edit mode.

When you drag the target shape's Weight slider, you see the effect of the corrective shape change influence on the skin mesh.

Transform-space corrective shapes

To create a transform-based post-skinning corrective shape

1. Follow the first six steps as for the tangent-space process above.
2. In the Add Blend Shape Target Options, select Transform Space from the Type list to create a transform-based target shape for this blend shape deformer.
3. In the Transform Name box, enter the name of the joint to which you want to associate the corrective target shape, or select the joint in the view or Outliner and click the Use Selected button. Click Apply and Close

   A blue target icon appears beside the target shape's name in the tree to indicate that it is transform based.

4. Follow the remaining steps for editing the targe shape as described in the tangent-space process above.