Set a constant fat offset for Sliding deformation

User Guide > Rigging > Maya Muscle > Skin Deformation >

Sliding deformation causes the skin mesh to move outside of any bone or muscle it hits. Sometimes you may model your mesh very precisely. If a muscle or bone causes the mesh to move out in the default state, you may prefer to allow the skin to stay below the surface of the mesh or bone, in essence keeping the original sculpted model exactly as it was. You can use the useBind and allowNegFat attributes of the Muscle deformer to do this.

The useBind attribute stores the fat offset of the skin mesh to the closest bone/muscle and uses that offset throughout the deformation, even if the point is slid by another muscle. Usually, the fat value on each bone/muscle sets the offset between the object and the skin. Once useBind is enabled, this offset is stored per point on the skin and is used regardless of changes to the muscle or bone objects.

The result is that the "fat" or offset between the skin and any muscle is constant. If allowNegFat is on, it allows the fat or offset to be below or inside a muscle or bone, keeping the original mesh intact.

NoteThere are other options on the cMuscleObject nodes themselves, such as fat and reverseNormals that also affect how sliding works. Refer to cMuscleObject node for more information on those settings.

In addition, you can use Direction weights and Direction nodes to help adjust and control the way Sliding occurs. See cMuscleDirection node.

To set up useBind mode

Select the Muscle deformed object and go to the original bind pose state of the model.
Select Muscle > Skin Setup > Bind Fat on Muscle System from the main menu bar.
The fat distance is stored on the cMuscleSystem node, and the object returns to its modeled state.

It is important to note that using binding can cause undesirable effects when muscles slide away or to different areas on the mesh. This is because the offset from the muscle has been stored, so the change in fat can still be seen. This usually means that for characters, you may not want to use Bind Fat, but instead should make sure your muscles are inside of your original skin mesh.