What Is a Model Bone?
A complex computer-generated object, often called a model, is made up of many vertices and materials organized into a set of meshes. In the XNA Framework, a model is represented by the Model class. A model contains one or more meshes, each of which is represented by a ModelMesh class. Each mesh is associated with one bone represented by the ModelBone class.
The bone structure is set up to be hierarchical to make controlling each mesh (and therefore the entire model) easier. At the top of the hierarchy, the model has a Root bone to specify the overall position and orientation of the model. Each ModelMesh object contains a ParentBone and one or more ModelBone. You can transform the entire model using the parent bone as well as transform each individual mesh with its bone. To animate one or more bones, update the bone transforms during the render loop by calling Model.CopyAbsoluteBoneTransformsTo Method, which iterates the individual bone transforms to make them relative to the parent bone. To draw an entire model, loop through a mesh drawing each sub mesh.