Skeletal animation is a processor-efficient and relatively simple animation system that can simulate any jointed object, from people to insects to machinery.
The titular skeleton is a hierarchy of jointed but individually rigid bones that are manipulated in the same way as a real skeleton. Vertexes are 'enveloped' to the appropriate bone and move with it; the bone in turn moves with the bones above it (e.g. the hand follows the forearm). Polygons that cover joints between bones stretch and compress as the skeleton moves.
- A bone is rigid
- The vertices enveloped to any given bone move as one unit. A skeletal animation cannot move them relative to each other (a flex animation can).
- A bone has only one parent
- A skeletons are organised into trees, branching out from a root. Webs/meshes of bones are not possible.
- Skeletons require hierarchy
- While it is theoretically possible to animate gasses or liquids with bones, it's an inefficient and overwrought solution. Use particles to create such effects.