Skeletal animation is a processor-efficient and relatively easy 3D animation system applicable to any jointed model: from humans to insects to mechanical machinery. It is not helpful for animating fluid structures like liquids or gaseous particles.
A skeleton is a system of rigid bones which determines the rendered model's (changing) pose. The model's Mesh vertices are enveloped to the bones and follow their parentbones' movements. Because the mesh is deformable, weightmapped polygons around skeletal joints may stretch and compress as the joints are flexed.
Each Skeleton is arranged in a bonetree hierarchy, so moving a bone high up in the hierarchy causes all of its child bones to move in response; eg. moving the "forearm" forward causes the "hand" to move forward by the same distance and in the same direction.
- Vertex animation is used to morph mesh vertices directly, eg animating faces.
- Particle animation is used to animate a point cloud of particle sprites.
- $sequences cannot re-scale bones dynamically (though this can be achieved through other means)
- $bonemerge allows sub-models to be included in the main model's sequences.