Skeletal animation is the use of “bones” to animate a model rather than editing and moving each vertex or face manually. Each vertex is attached to a bone (or in some cases multiple bones). A bone or joint is simply a control point for a group of vertices. These are similar in concept to joints in our own bodies, such as our knee or wrist joint. When the bone moves, every vertex attached to it moves as well, as shown in Figure 5.2. Even the movement of bones themselves can cause changes to other bones. This helps the model move appropriately, because movements in one portion of the body affect other parts of the body, as in real life. Consequently, programmers are required to work with the bones to calculate the transformations for the individual vertices. Although this can be more work, the result is definitely worth it.
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Figure 5.2 Vertex animation requires you to move every vertex, whereas skeletal animation enables you to move only the bones within the model; the vertices will follow.