本篇是XFile網格的應用（1）的續篇。

.X文件的數據裝入

在上一篇的.X文件中，主場景框架 Scene_Root提供了一個變換矩陣和一個子框架Quad。這個Quad具有一個Mesh網格（包括頂點，材質，紋理等數據），其中 Scene_Root框架的變換矩陣（實際為單位矩陣）說明了Quad子框架的Mesh網格數據應做的變換，以正確擺放在父框架的空間中（這里指世界空間）。對于僅含有單一網格的.X文件來說，利用D3DXLoadMeshFromX函數可實現簡單網格數據的加載。

來看看D3DXLoadMeshFromX的具體使用說明：

Loads a mesh from a DirectX .x file.

 HRESULT D3DXLoadMeshFromX( 
   LPCTSTR   pFilename  , 
   DWORD   Options  , 
   LPDIRECT3DDEVICE9   pD3DDevice  , 
   LPD3DXBUFFER *   ppAdjacency  , 
   LPD3DXBUFFER *   ppMaterials  , 
   LPD3DXBUFFER *   ppEffectInstances  , 
   DWORD *   pNumMaterials  , 
   LPD3DXMESH *   ppMesh 
 ); 

Parameters

pFilename

[in] Pointer to a string that specifies the filename. If the compiler settings require Unicode, the data type LPCTSTR resolves to LPCWSTR. Otherwise, the string data type resolves to LPCSTR. See Remarks.

Options

[in] Combination of one or more flags from the D3DXMESH enumeration, which specifies creation options for the mesh.

pD3DDevice

[in] Pointer to an IDirect3DDevice9 interface, the device object associated with the mesh.

ppAdjacency

[out] Pointer to a buffer that contains adjacency data. The adjacency data contains an array of three DWORDs per face that specify the three neighbors for each face in the mesh. For more information about accessing the buffer, see ID3DXBuffer.

ppMaterials

[out] Pointer to a buffer containing materials data. The buffer contains an array of D3DXMATERIAL structures, containing information from the DirectX file. For more information about accessing the buffer, see ID3DXBuffer .

ppEffectInstances

[out] Pointer to a buffer containing an array of effect instances, one per attribute group in the returned mesh. An effect instance is a particular instance of state information used to initialize an effect. See D3DXEFFECTINSTANCE. For more information about accessing the buffer, see ID3DXBuffer .

pNumMaterials

[out] Pointer to the number of D3DXMATERIAL structures in the ppMaterials array, when the method returns.

ppMesh

[out] Address of a pointer to an ID3DXMesh interface, representing the loaded mesh.

Return Values

If the function succeeds, the return value is D3D_OK. If the function fails, the return value can be one of the following values: D3DERR_INVALIDCALL, E_OUTOFMEMORY.

Remarks

The compiler setting also determines the function version. If Unicode is defined, the function call resolves to D3DXLoadMeshFromXW. Otherwise, the function call resolves to D3DXLoadMeshFromXA because ANSI strings are being used.

All the meshes in the file will be collapsed into one output mesh. If the file contains a frame hierarchy, all the transformations will be applied to the mesh.

For mesh files that do not contain effect instance information, default effect instances will be generated from the material information in the .x file. A default effect instance will have default values that correspond to the members of the D3DMATERIAL9 structure.

The default texture name is also filled in, but is handled differently. The name will be Texture0@Name, which corresponds to an effect variable by the name of "Texture0" with an annotation called "Name." This will contain the string file name for the texture.

來看看參數Option可以指定的網格創建模式：

Flags used to specify creation options for a mesh.

typedef enum D3DXMESH
{
    D3DXMESH_32BIT = 0x001,
    D3DXMESH_DONOTCLIP = 0x002,
    D3DXMESH_POINTS = 0x004,
    D3DXMESH_RTPATCHES = 0x008,
    D3DXMESH_NPATCHES = 0x4000,
    D3DXMESH_VB_SYSTEMMEM = 0x010,
    D3DXMESH_VB_MANAGED = 0x020,
    D3DXMESH_VB_WRITEONLY = 0x040,
    D3DXMESH_VB_DYNAMIC = 0x080,
    D3DXMESH_VB_SOFTWAREPROCESSING = 0x8000,
    D3DXMESH_IB_SYSTEMMEM = 0x100,
    D3DXMESH_IB_MANAGED = 0x200,
    D3DXMESH_IB_WRITEONLY = 0x400,
    D3DXMESH_IB_DYNAMIC = 0x800,
    D3DXMESH_IB_SOFTWAREPROCESSING = 0x10000,
    D3DXMESH_VB_SHARE = 0x1000,
    D3DXMESH_USEHWONLY = 0x2000,
    D3DXMESH_SYSTEMMEM = 0x110,
    D3DXMESH_MANAGED = 0x220,
    D3DXMESH_WRITEONLY = 0x440,
    D3DXMESH_DYNAMIC = 0x880,
    D3DXMESH_SOFTWAREPROCESSING = 0x18000,
} D3DXMESH, *LPD3DXMESH;

Constants

D3DXMESH_32BIT

The mesh has 32-bit indices instead of 16-bit indices. See Remarks.

D3DXMESH_DONOTCLIP

Use the D3DUSAGE_DONOTCLIP usage flag for vertex and index buffers.

D3DXMESH_POINTS

Use the D3DUSAGE_POINTS usage flag for vertex and index buffers.

D3DXMESH_RTPATCHES

Use the D3DUSAGE_RTPATCHES usage flag for vertex and index buffers.

D3DXMESH_NPATCHES

Specifying this flag causes the vertex and index buffer of the mesh to be created with D3DUSAGE_NPATCHES flag. This is required if the mesh object is to be rendered using N-patch enhancement using Direct3D.

D3DXMESH_VB_SYSTEMMEM

Use the D3DPOOL_SYSTEMMEM usage flag for vertex buffers.

D3DXMESH_VB_MANAGED

Use the D3DPOOL_MANAGED usage flag for vertex buffers.

D3DXMESH_VB_WRITEONLY

Use the D3DUSAGE_WRITEONLY usage flag for vertex buffers.

D3DXMESH_VB_DYNAMIC

Use the D3DUSAGE_DYNAMIC usage flag for vertex buffers.

D3DXMESH_VB_SOFTWAREPROCESSING

Use the D3DUSAGE_SOFTWAREPROCESSING usage flag for vertex buffers.

D3DXMESH_IB_SYSTEMMEM

Use the D3DPOOL_SYSTEMMEM usage flag for index buffers.

D3DXMESH_IB_MANAGED

Use the D3DPOOL_MANAGED usage flag for index buffers.

D3DXMESH_IB_WRITEONLY

Use the D3DUSAGE_WRITEONLY usage flag for index buffers.

D3DXMESH_IB_DYNAMIC

Use the D3DUSAGE_DYNAMIC usage flag for index buffers.

D3DXMESH_IB_SOFTWAREPROCESSING

Use the D3DUSAGE_SOFTWAREPROCESSING usage flag for index buffers.

D3DXMESH_VB_SHARE

Forces the cloned meshes to share vertex buffers.

D3DXMESH_USEHWONLY

Use hardware processing only. For mixed-mode device, this flag will cause the system to use hardware (if supported in hardware) or will default to software processing.

D3DXMESH_SYSTEMMEM

Equivalent to specifying both D3DXMESH_VB_SYSTEMMEM and D3DXMESH_IB_SYSTEMMEM.

D3DXMESH_MANAGED

Equivalent to specifying both D3DXMESH_VB_MANAGED and D3DXMESH_IB_MANAGED.

D3DXMESH_WRITEONLY

Equivalent to specifying both D3DXMESH_VB_WRITEONLY and D3DXMESH_IB_WRITEONLY.

D3DXMESH_DYNAMIC

Equivalent to specifying both D3DXMESH_VB_DYNAMIC and D3DXMESH_IB_DYNAMIC.

D3DXMESH_SOFTWAREPROCESSING

Equivalent to specifying both D3DXMESH_VB_SOFTWAREPROCESSING and D3DXMESH_IB_SOFTWAREPROCESSING.

Remarks

A 32-bit mesh (D3DXMESH_32BIT) can theoretically support (2^32)-1 faces and vertices. However, allocating memory for a mesh that large on a 32-bit operating system is not practical.

參數ppAdjacency, ppMaterials, ppEffectInstances的類型都是LPD3DXBUFFER，它實際上是指向ID3DXBUFFER的指針：

The ID3DXBuffer interface is used as a data buffer, storing vertex, adjacency, and material information during mesh optimization and loading operations. The buffer object is used to return arbitrary length data. Also, buffer objects are used to return object code and error messages in methods that assemble vertex and pixel shaders.

ID3DXBuffer Members

Method	Description
ID3DXBuffer::GetBufferPointer	Retrieves a pointer to the data in the buffer.
ID3DXBuffer::GetBufferSize	Retrieves the total size of the data in the buffer.

Remarks

The ID3DXBuffer interface is obtained by calling the D3DXCreateBuffer function.

The LPD3DXBUFFER type is defined as a pointer to the ID3DXBuffer interface.

typedef interface ID3DXBuffer ID3DXBuffer;
typedef interface ID3DXBuffer *LPD3DXBUFFER;

來看看ID3DXBuffer提供的兩個方法，先來看看GetBufferPointer的具體使用信息：
 

再來看看GetBufferSize的具體使用信息：

Retrieves the total size of the data in the buffer.

DWORD GetBufferSize();

Parameters
None.

Return Values
Returns the total size of the data in the buffer, in bytes.

ID3DXBuffer可利用DirectX API函數D3DXCreateBuffer來創建，不過，一般不需要直接創建，下面是該函數的具體使用信息：

Creates a buffer object.

HRESULT D3DXCreateBuffer(
  DWORD NumBytes,
  LPD3DXBUFFER * ppBuffer
);

Parameters

NumBytes
[in] Size of the buffer to create, in bytes.

ppBuffer
[out] Address of a pointer to an ID3DXBuffer interface, representing the created buffer object.

Return Values

If the function succeeds, the return value is D3D_OK. If the function fails, the return value can be one of the following: E_OUTOFMEMORY.

利用pNumMaterials指針參數可獲得網格mesh所使用的材質的數量，ppMesh參數則是返回的一個ID3DXMESH 接口的指針地址，利用ID3DXMESH 接口提供的方法，可對裝入的網格數據進行讀取，優化和渲染等。

由于利用D3DXLoadMeshFromX函數裝入的材質和紋理貼圖文件名被封裝在一個擴展的D3DXMATERIAL結構體內，因此通常需要將材質取出，放入材質數組中，將紋理貼圖文件名取出，創建相應的紋理對象，再將這些紋理對象放入紋理對象數組中，以方便后續的紋理網格渲染。

來看看D3DXMATERIAL的具體信息：
 
其中用到了結構體D3DMATERIAL9，它的具體定義是：
 
下面的代碼演示了怎樣加載.X文件，以及加載后怎樣獲得相應的數據。

 IDirect3D9*         _d3d;
 IDirect3DDevice9*   _d3d_device;
 ID3DXBuffer*        _adjacency_buffer;
 ID3DXBuffer*        _material_buffer;
 D3DMATERIAL9*       _material_array;
 IDirect3DTexture9** _texture_array;

 DWORD               _num_materials;
 ID3DXMesh*          _mesh;

//------------------------------------------------------------------------------------
// Load .X file
//------------------------------------------------------------------------------------
bool BASIC_XFILE::Load_XFile(char* x_filename)
{
    // Loads a mesh from a DirectX .x file
    if(FAILED(D3DXLoadMeshFromX(
        x_filename,             // Pointer to a string that specifies the filename
        D3DXMESH_MANAGED,       // specifies creation options for the mesh
        _d3d_device,            // Pointer to an IDirect3DDevice9 interface
        &_adjacency_buffer,     // Pointer to a buffer that contains adjacency data
        &_material_buffer,      // Pointer to a buffer containing materials data
        NULL,                   // Pointer to a buffer containing an array of effect instances
        &_num_materials,        // Pointer to the number of D3DXMATERIAL structures 
        &_mesh)))               // Address of a pointer to an ID3DXMesh interface
    {
        MessageBox(NULL, "Load .X file failed.", "ERROR", MB_OK);
        return false;
    }

    // invalid data
    if(_material_buffer == NULL || _num_materials == 0)
        return false;

    // retrieves a pointer to the data in the buffer
    D3DXMATERIAL* material = (D3DXMATERIAL*) _material_buffer->GetBufferPointer();

    if(material != NULL)
    {
        // allocate memory for material array and texture array
        _material_array = new D3DMATERIAL9[_num_materials];
        _texture_array  = new IDirect3DTexture9*[_num_materials];    

        for(DWORD i = 0; i < _num_materials; i++)
        {
            // assign material to array
            _material_array[i] = material[i].MatD3D;

            if(material[i].pTextureFilename != NULL)
            {
                if(FAILED(D3DXCreateTextureFromFile(_d3d_device, material[i].pTextureFilename, &_texture_array[i])))
                    _texture_array[i] = NULL;
            }
        }
    }

    // Generates a mesh with reordered faces and vertices to optimize drawing performance. 
    // This method reorders the existing mesh.
    _mesh->OptimizeInplace(D3DXMESHOPT_COMPACT | D3DXMESHOPT_ATTRSORT | D3DXMESHOPT_VERTEXCACHE,
        (DWORD*) _adjacency_buffer->GetBufferPointer(), NULL, NULL, NULL);

    _material_buffer->Release();
    _adjacency_buffer->Release();

    return true;
}

Mesh數據的處理

執行D3DXLoadMeshFromX函數完成.X文件的加載后，Mesh的各種數據將存放在頂點緩沖區，頂點索引緩沖區，材質緩沖區，鄰接頂點緩沖區，特效屬性緩沖區，網格緩沖區中。其中，材質緩沖區（包含材質信息和紋理貼圖文件名信息），鄰接頂點緩沖區以及特效屬性緩沖區的地址由 D3DXLoadMeshFromX函數成功執行后返回，其他的緩沖區地址可利用ID3DXMesh接口函數來獲得。

.X網格的渲染和優化就是使用上面緩沖區的數據來進行的。頂點緩沖區給出了整個網格的頂點坐標列表（包括頂點坐標和頂點紋理坐標），頂點索引緩沖區給出了每個三角形面的頂點構成信息（三個頂點的索引值），從而間接給出了整個網格的所有三角形面的頂點信息說明，屬性緩沖區為每個三角形面的一個網格子集編號，即給出了網格的每個三角形面的分組號。具有同一個Subset編號的三角形，將使用相同的材質和紋理對象進行渲染。

Mesh網格的渲染，可以用一個for循環來進行，循環的次數為總的材質數。每一次循環都將那些具有相同Subset子集號的三角形面渲染出來，即渲染每個子集Subset。不過每次循環首先要設置渲染管道線的材質和紋理對象，如下所示：

//------------------------------------------------------------------------------------
// Render mesh.
//------------------------------------------------------------------------------------
void BASIC_XFILE::Render()
{
    // Clear a render target and the depth buffer
    _d3d_device->Clear(0, NULL, D3DCLEAR_TARGET | D3DCLEAR_ZBUFFER, D3DCOLOR_XRGB(0, 0, 0), 1.0f, 0);

    _d3d_device->BeginScene();

    // draw all face in the mesh
    for(DWORD i = 0; i < _num_materials; i++)
    {
        // Sets the material properties for the device
        _d3d_device->SetMaterial(&_material_array[i]);

        // Assigns a texture to a stage for a device
        _d3d_device->SetTexture(0, _texture_array[i]);

        // Draws a subset of a mesh
        _mesh->DrawSubset(i);
    }

    _d3d_device->EndScene();

    // Presents the contents of the next buffer in the sequence of back buffers owned by the device
    _d3d_device->Present(NULL, NULL, NULL, NULL);
}

上面的代碼中使用Clear對Z緩沖區進行了清除，因此必須在初始化D3D設備時，開啟Z緩沖區，否則該函數調用失敗并且屏幕將出現重影。

D3DPRESENT_PARAMETERS present_param;

present_param.EnableAutoDepthStencil = TRUE;

如果沒有加入上面的代碼，則出現重影，如下圖所示：



Render函數中使用DrawSubset函數來渲染每一個Mesh子集，該函數只需要指定一個子集號，就可將網格中具有該子集號的三角形面渲染出來，下面是該函數的具體使用信息：
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