Morph target animation
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Morph target animation (or per-vertex animation) is a method of 3D computer animation that is sometimes used as an alternative to skeletal animation. Morph target animation is stored as a series of vertex positions. In each keyframe of the animation, the vertices are moved to a different position.
Depending on the renderer, the vertices will move along paths to fill in the blank time between the keyframes or the renderer will simply switch between the different positions, creating a somewhat jerky look. The former is used more commonly.
There are advantages to using morph target animation over skeletal animation. The artist has more control over the movements because he or she can define the individual positions of the vertices within a keyframe, rather than being constrained by skeletons. This can be useful for animating cloth, skin, and facial expressions because it can be difficult to conform those things to the bones that are required for skeletal animation.
However, there are also disadvantages. Vertex animation is usually a lot more time-consuming than skeletal animation because every vertex position would have to be calculated. (3D models in modern computer and video games often contain something to the order of 4,000-9,000 vertices.) Also, in methods of rendering where vertices move from position to position during in-between frames, a distortion is created that doesn't happen when using skeletal animation. This is described by critics of the technique as looking "shaky". On the other hand, this distortion may be part of the desired "look".
Not all morph target animation has to be done by actually editing vertex positions. It is also possible to take vertex positions found in skeletal animation and then use those rendered as morph target animation.
Sometimes, animation composed in one 3D application suite needs to be transferred to another, as for rendering. To avoid export issues, native animation formats will often be converted to morph target animation. This is sometimes necessary due to the different ways 3D application suites implement bones and other special effects.
