D3DXSkinMesh

Applications use the methods of the D3DXSkinMesh class to manipulate skin mesh objects.

The D3DXSkinMesh class is obtained by calling one of the following methods.

• D3DX8.CreateSkinMesh
• D3DX8.CreateSkinMeshFromMesh
• D3DX8.CreateSkinMeshFVF

To load a skin mesh from a Microsoft® DirectX® X file data object, use the D3DX8.LoadSkinMeshFromXof method.

Skinning is the technique of having different vertices of a mesh be transformed by multiple transform matrices and the results of the vertex being transformed with each individual matrix blended together to obtain the final transformed vertex.

This process is commonly called skinning because it is used to deform a mesh defining a skin of some character based on the animation of a skeleton of bones. In the simplest case of rigid animation, different parts of the character mesh are associated with a unique skeleton bone and vertices are transformed using the transform of that bone.

When discussing skinning, it is useful to define the following terms.

• Skin. The triangle mesh being rendered using deformations. Typically this is the model of the character in some convenient pose.
• Bone. A transform matrix that affects one or more vertices of the skin.
• Skeleton. A hierarchy of all the bones that affect a skin mesh.
• Pose. A set of bone transforms that completely defines the transforms for all the bones that affect a given skin mesh.
• Initial Pose. This is the pose in which the mesh was associated with the skeleton. When the skeleton is in this pose, the deformed mesh is identical to the original undeformed mesh.
• Bone Space Transform. This transform transforms the mesh into the local space of a particular bone.
• Bone Weight. The amount of influence a bone has on a given vertex. A weight of 1 means that the vertex is only affected by that bone and 0 means it is unaffected by the bone. The sum of weights of all the bones that affect a vertex should add up to 1 for all vertices.

A skinned character is defined by a set of meshes and a set of bones that affect the vertices of the meshes. The bones are represented as a transform hierarchy. For each mesh, there is a matrix for every bone that affects it that transforms the mesh into the local coordinate space of the bone. This matrix is the bone space transform of the bone for the mesh. This is defined at the time the skeleton is associated with the mesh in the authoring process.

The methods of the D3DXSkinMesh class can be organized into the following groups.