Graphics Reference
In-Depth Information
We apply the same concept to the armature of a mesh. We have a root bone, and each
subsequent bone is parented by the root bone or another bone that ultimately resolves
it's parentage to this root bone. In this manner, if we move the root bone, the whole body
moves with it; but if we move the shoulder, then only the arm moves with it.
The left-most figure in the following screenshot shows an example of an armature of a
simple mesh that has been divided into four segments. In this example, the root bone
is the bottom-most bone, and each subsequent bone is parented by it's previous bone.
The position or pose shown in this figure is referred to as the bind pose or rest pose,
and it represents the default starting transformation of each bone at the time the mesh
was bound to the armature or rigged.
Simply having an armature in place is not enough for it to apply forces upon the skin. We must
bind the mesh to the armature and specify how each of the bones will influence the vertices.
By applying weights, known as bone-weights or blend-weights, to the vertex of each of the
influencing bones, our armature will be able to influence the placement of vertices.
In the following screenshot, the right-most figure shows how the vertices' bone-weights
have been applied in relation to the top-most bone in the hierarchy. The cooler the color,
lesser the influence of the bone on the vertex (where the blue color at the bottom is 0.0);
and the warmer the color, the greater the influence of the bone (where the red color at the
top is 1.0). As seen from the gradual cooling of the bone-weights toward the next bone, it is
clear that more than one bone can have an influence upon a vertex.
Impact of bones upon the vertices of a mesh (from left to right: bind pose, a pose, and bone-weights)
