When you're working with skinned characters, it's common to need a special shape to fix a skin deformation problem when a character is in a certain pose. Deformation problems typically occur at a character's articulation points, such as the shoulder, underarm, knee, and groin areas.
Using the Pose Editor, you can fix these problems with a technique known as pose space deformation (PSD). You first create a Pose Interpolator node for a selected joint, and each node contains different poses. For each pose, you rotate or move the character's joint where there is a skin deformation problem, and then create or use an associated corrective blend shape (called a pose shape) to fix the problem. These blend shapes are then automatically used whenever the character's joint reaches that pose. You can set the strength (weight) of each shape for its pose as you like, and have them interpolate between each other and the skin mesh.
Tips for working with pose space deformations
When you're creating corrective pose shapes, it's best practice to first build the shapes for all the extreme poses and then add the in-between pose shapes where necessary.
However, if you want to simplify this workflow and create the shapes "as you go", you may run into problems where the weight value of each additional pose increases. To avoid this issue, select a specific pose and activate the Independent option in the Advanced Settings panel of the Pose Editor (choose in the Pose Editor, or right-click a Pose name there and choose Show Advanced Settings to show this panel). When a pose is independent, it is removed from the normalization calculations with the other poses, and can be adjusted only by its rotation and/or translation falloff.
To create poses with associated corrective shapes on a character
- Select the character's joint that corresponds to the skin area whose deformation you want to fix. This will be the neutral pose for the shape.
- To create a new Pose Interpolator mode, do one of the following:
- Choose in the Modeling, Rigging, or Animation menu sets.
- Open the
Pose Editor and click the
Create Pose Interpolator button or choose
>
.
- If you click the Create Pose Interpolator button, a neutral pose is automatically created.
- If you select
>
, you can decide to select the
Add Neutral Poses option (the default) or not. For best results, you should select this option because a neutral pose ensures that no other poses added to this Pose Interpolator node will be activated when the joint is at this neutral pose.
-
The new node appears in the Pose Interpolators panel of the Pose Editor. By default, the name is the joint name with a "_poseInterpolator" suffix.
- Select this node to see the default poses for it in the Pose panel on the right. Only the three neutral poses are displayed at first.
- Rotate or move the joint into a position where you want to add a pose with an associated corrective shape. This will be the first extreme pose where you want to add a shape.
- In the Pose Editor, select the Pose Interpolator node and click the
Add Pose button, or choose
>
to add this current state as a new pose.
- If this Pose Interpolator node is not already connected to a Blend Shape deformer, the Create Pose Shape window opens in which you can create one.
- If there is already a blend shape deformer on the skin mesh, the Add Pose Options opens in which you can select the Pose Type (Swing, Swing and Twist, or Twist).
- Give this new pose a descriptive name. By default, the name is driverName_rx_ry_rz, where driverName is the joint's name and rx/ry/rz are the joint's rotation values in this pose.
- When you create the pose, its Edit button is automatically activated so that you can immediately edit the mesh. Make sure that the pose's Weight value is not 0 (1 is usually the best).
- Modify the position of the vertices on the skin using the Sculpting tools, or any of the Transform tools (Move, Rotate, or Scale).
Each modification you make is a delta to the vertex positions of the skin's original shape. This particular information is stored for that pose shape and used by the Pose Interpolator node to calculate the deformations on the skin.
Note: Open the camera Tumble tool settings and turn on Tumble About: Tumble pivot and the Automatically set tumble pivot option. This automatically adjusts the camera's tumble pivot to your last selection or sculpting stroke. - When you're finished fixing the skin for this pose, click the Edit button to exit the mode.
- Pose the character or go to a frame in the timeline where the skin's mesh deforms in an undesirable way or you want to change the skin's shape.
- As before, click the
Add Pose button, or choose
>
to add this current state as a new pose.
- Click the pose's Edit button and use the Sculpting or Transform tools to modify the skin, then click Edit again to exit the mode when you're done.
- Rotate the affected joint to see how the pose shape blend into the rest of the skin. The weighting of the poses are normalized against each other as you rotate the joint. The weight value of the poses update from 0 (no weight) to 1 (full weight), depending on how close the joint rotation is to the stored pose.
- Double-click a pose in the panel, or right-click the pose and choose Go To Pose, to quickly return to that pose (it's applied at 100% weighting). For example, double-click on the neutral pose and then a pose you created to see how the corrective shape is automatically applied when the character is in that pose.
- Repeat this process of adding and editing poses to create as many pose-based shapes as you need for the character.
Now you need to correct or enhance the skin's deformation in this pose:
Now go on to the next extreme pose: