# Skinning Geometry

Broken-Joint Skeletons Keep in mind that you also have the option of binding only selected joints. In some circumstances, this can be quite useful. For example, if you set up what is known as a broken-joint skeleton, which uses additional bones outside the main skeleton hierarchy as deformers, these additional joints are usually constrained to the main hierarchy using parent constraints. By using parent constraints, the joints “float” outside the main hierarchy, giving them a level of freedom of movement to create special deformation effects. (Sometimes floating joints are used for facial animation instead of or in addition to blendshape deformers.) When skinning a broken rig to the skeleton, select the floating joints along with the joints in the main hierarchy when the smooth bind operation is performed. The following are the relevant settings: Bind methodâã‡âã‰ âã‡âã‰ The bind method determines how joints influence vertices, by either following the skeleton’s hierarchy or simply using whichever joint is the closest. The hierarchy of the giraffe is complete and calls for every bone to be weighted; however, for the tips, use Closest In Hierarchy. Include methodâã‡âã‰ âã‡âã‰ The include method dictates which vertices are included in the initial volumes. Your options are Closest Volume and Minimum Weight. Choosing Minimum Weight opens an additional option to set the length of the volume. By default this is .25, causing each volume to be 25 percent longer than the bone to which it is attached. Most characters will have a different area of influence based on its location. For instance, the giraffe’s knee needs to have a smaller falloff compared to the torso. Choose Closest Volume. There are two types of volumes you can use, a cylinder or a capsule: A cylinder w ãu ill deliver a hard edge. ãu The capsule is rounded at its ends, providing a smoother falloff. Keep the capsule turned on. Skinning methodâã‡âã‰ âã‡âã‰ The skinning method has the greatest impact on your bind. You can use Classic Linear, Dual Quaternion, or a blend of both. ãu Dual Quaternion provides the most suitable deformations for realistic characters. It preserves the volume of a mesh when a joint is twisted or rotated. ãu Classic Linear does not preserve volume and produces a visible shrinking of the geometry. Take a look at FigureÂ€7.34 to see the differences between the two. The last two settings relate to how many influences a single vertex can have. It is important to remember that joints are not the only nodes that can be bound to geometry. Other geometry can also be used and is therefore considered an influence as well. Most weighted objects do not require more than four influences per vertex, which is Maya’s default. In addition, a lot of game engines have a hard limit of four influences on a single vertex. After binding, you can keep the influences locked to four by selecting Maintain Max Influences.

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