skinning bone weights of a vertex in the mesh.
each vertex is skinned with up to four bones. all weights should sum up to one. weights and bone indices should be defined in the order of decreasing weight. if a vertex is affected by less than four bones, the remaining weights should be zeroes.
skinning weight for first bone.
skinning weight for second bone.
skinning weight for third bone.
skinning weight for fourth bone.
index of first bone.
index of second bone.
index of third bone.
index of fourth bone.