Skinned Meshes

Basics of bone hierarchies

在DX9中使用LPD3DXFRAME作为基础的节点数据结构，内容有：

struct D3DXFRAME {
LPSTR Name; //Name of bone
D3DXMATRIX TransformationMatrix; //Local bone pos, rot & sca
LPD3DXMESHCONTAINER pMeshContainer; //Mesh connected to bone
D3DXFRAME* pFrameSibling; //Sibling bone pointer
D3DXFRAME* pFrameFirstChild; //First child bone
};

值得注意的是这里节点是有同层级的，以下是输出节点的测试代码：

void PrintHierarchy(D3DXFRAME *bone)
{
    //Print Bone Name
    cout << bone->Name;

    //Traverse Siblings
    if(bone->pFrameSibling != NULL)
        PrintHierarchy(bone->pFrameSibling);
        
    //Traverse Children
    if(bone->pFrameFirstChild != NULL)
        PrintHierarchy(bone->pFrameSibling);
}

Loading bone hierarchies from an .x file

使用 D3DXLoadMeshHierarchyFromX 方法加载骨骼数据，方法如下：

HRESULT D3DXLoadMeshHierarchyFromX(
LPCSTR Filename,
DWORD MeshOptions,
LPDIRECT3DDEVICE9 pDevice,
LPD3DXALLOCATEHIERARCHY pAlloc,
LPD3DXLOADUSERDATA pUserDataLoader,
LPD3DXFRAME* ppFrameHierarchy,
LPD3DXANIMATIONCONTROLLER* ppAnimController
);

其中需要自定义实现以下ID3DXAllocateHierarchy接口，其中有四个方法需要实现：

HRESULT CreateFrame(LPCSTR Name, LPD3DXFRAME* ppNewFrame) override;
HRESULT CreateMeshContainer(THIS_
	LPCSTR Name,
	CONST D3DXMESHDATA* pMeshData,
	CONST D3DXMATERIAL* pMaterials,
	CONST D3DXEFFECTINSTANCE* pEffectInstances,
	DWORD NumMaterials,
	CONST DWORD* pAdjacency,
	LPD3DXSKININFO pSkinInfo,
	LPD3DXMESHCONTAINER* ppNewMeshContainer) override;
HRESULT DestroyFrame(LPD3DXFRAME pFrameToFree)override;
HRESULT DestroyMeshContainer(LPD3DXMESHCONTAINER pMeshContainerBase)override;

这个功能主要让我们自定义初始化骨骼节点数据，具体的结构功能如下：

HRESULT BoneHierarchyLoader::CreateMeshContainer(...)
{
    //Create new Bone Mesh
    ...
    
    //Get mesh data here
    ...
    
    //Copy materials and load textures (like with a static mesh)
    ...
    if(pSkinInfo != NULL)
    {
        //Store Skin Info and convert mesh to Index Blended Mesh
        ...
    }

    //Set ppNewMeshContainer to newly created boneMesh container
    ...
}

Software skinning

主要的步骤：

• Overload D3DXFRAM
• Overload D3DXMESHCONTAINER
• Implement the ID3DXAllocateHierarchy interface
• Load a bone hierarhy and associated meshes, skinning information, erc, with the D3DXLoadMeshHierachyFromX() function
• For each frame, update the skeleton pose (i.e. the SkinnedMesh::UpdateMatrices() function)
• Update the target mesh using ID3DXSkinInfo::UpdateSkinnedMesh()
• Render the target mesh as a common static mesh

CPU蒙皮不需要我们自己处理权重计算，应该是boneMesh->pSkinInfo->UpdateSkinnedMesh(boneMesh->currentBoneMatrices, NULL, src, dest);这个方法里面计算。

Hardware skinning

主要的步骤：

• Overload D3DXFRAM
• Overload D3DXMESHCONTAINER
• Implement the ID3DXAllocateHierarchy interface
• Load a bone hierarhy and associated meshes, skinning information, erc, with the D3DXLoadMeshHierachyFromX() function
• For each frame, update the skeleton pose (i.e. the SkinnedMesh::UpdateMatrices() function)
• Upload the Matrix Palette (bone matrices) to the vertex shader
• Render the Index Blended Mesh using the vertex shader

GPU蒙皮需要自己在shader中处理权重混合，一个顶点受四根骨骼影响，如下图：

Rendering static meshes in a bone hierarchy

静态mesh还是有骨骼，所以前几个步骤是一样：

• Overload D3DXFRAM
• Overload D3DXMESHCONTAINER
• Implement the ID3DXAllocateHierarchy interface
• Load a bone hierarhy and associated meshes, skinning information, erc, with the D3DXLoadMeshHierachyFromX() function
• Set bone world transform to the static mesh, in order to animate static with bone
• Render static mesh with boneMesh->OriginalMesh->DrawSubset(i);