利用.x文件模型渲染三維模型，首先需要將.x文件中的各種數據分別加載到內存中，主要包括頂點數據、材質數據和紋理數據等。

網格模型接口ID3DXMESH

Direct3D擴展實用庫定義了多邊形網格模型接口ID3DXMesh來表示一個復雜的三維物體模型，它是一個COM接口，繼承自ID3DXBaseMesh。

Direct3D擴展實用庫函數D3DXCreateMesh()可用于創建一個Direct3D網格模型對象，該函數聲明如下:

Creates a mesh object using a declarator.

HRESULT D3DXCreateMesh(
  DWORD NumFaces,
  DWORD NumVertices,
  DWORD Options,
  CONST LPD3DVERTEXELEMENT9 * pDeclaration,
  LPDIRECT3DDEVICE9 pD3DDevice,
  LPD3DXMESH * ppMesh
);

Parameters

NumFaces

[in] Number of faces for the mesh. The valid range for this number is greater than 0, and one less than the maximum DWORD (typically 65534), because the last index is reserved.

NumVertices

[in] Number of vertices for the mesh. This parameter must be greater than 0.

Options

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

pDeclaration

[in] Array of D3DVERTEXELEMENT9 elements, describing the vertex format for the returned mesh. This parameter must map directly to a flexible vertex format (FVF).

pD3DDevice

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

ppMesh

[out] Address of a pointer to an ID3DXMesh interface, representing the created mesh 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: D3DERR_INVALIDCALL, E_OUTOFMEMORY.

D3DXMESH

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.

一般情況下，參數Option置為D3DMESH_SYSTEMMEM或D3DMESH_MANAGED，表示對Direct3D頂點緩沖區和索引緩沖區使用D3DPOOL_SYSTEMMEM或D3DPOOL_MANAGED內存。

調用D3DXCreateMesh()函數創建了網格模型對象后，還需要為其載入模型數據，而載入模型數據是比較復雜的。所以在大多數情況下，不直接調用該函數，它被封裝在Direct3D擴展實用庫函數中，由Direct3D在內部完成網格模型對象的創建和模型數據的載入操作。

通過.x文件生成網格模型

復雜的三維模型實際上是由許許多多的多邊形構成的，所以首先需要得到這些構成模型的多邊形。使用Direct3D功能擴展庫函數D3DXLoadMeshFromX()，可以從.X文件中提取多邊形信息（包括頂點坐標、顏色、法向量和紋理信息等），生成網格模型。該函數的聲明如下：

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.

LPD3DXBUFFER因數據操作的方便性而誕生，它的好處是可以存儲頂點位置坐標、材質、紋理等多種類型的Direct3D數據，而不必對每種數據聲明一種函數接口類型。可使用接口函數ID3DXBuffer::GetBufferPointer()獲取緩沖區中的數據，使用ID3DXBuffer::GetBufferSize()獲取緩沖區數據大小。

載入材質和紋理

如果函數D3DXLoadMeshFromX()調用成功，那么參數ppMaterials就會獲取.x文件中三維模型導出的材質和紋理信息，而pNumMaterials則會獲得材質的數目，將材質和紋理信息從中提取出來的代碼如下：

bool init_geometry()
{
	ID3DXBuffer* material_buffer;

	/*
	 D3DXLoadMeshFromXA(
        LPCSTR pFilename, 
        DWORD Options, 
        LPDIRECT3DDEVICE9 pD3DDevice, 
        LPD3DXBUFFER *ppAdjacency,
        LPD3DXBUFFER *ppMaterials, 
        LPD3DXBUFFER *ppEffectInstances, 
        DWORD *pNumMaterials,
        LPD3DXMESH *ppMesh);
	*/

	if(FAILED(D3DXLoadMeshFromX("airplane.x", D3DXMESH_MANAGED, g_device, NULL, &material_buffer, NULL,
								&g_num_materials, &g_mesh)))
	{
		MessageBox(NULL, "Could not find airplane.x", "ERROR", MB_OK);
		return false;
	}

	D3DXMATERIAL* xmaterials = (D3DXMATERIAL*) material_buffer->GetBufferPointer();

	g_mesh_materials = new D3DMATERIAL9[g_num_materials];
	g_mesh_textures	 = new IDirect3DTexture9*[g_num_materials];

	for(DWORD i = 0; i < g_num_materials; i++)
	{
		g_mesh_materials[i] = xmaterials[i].MatD3D;

		// set ambient reflected coefficient, because .x file do not set it.
		g_mesh_materials[i].Ambient = g_mesh_materials[i].Diffuse;

		g_mesh_textures[i] = NULL;

		if(xmaterials[i].pTextureFilename != NULL && strlen(xmaterials[i].pTextureFilename) > 0)	
			D3DXCreateTextureFromFile(g_device, xmaterials[i].pTextureFilename, &g_mesh_textures[i]);	
	}

	material_buffer->Release();

	return true;
}

一個三維網格模型通常是由幾個子模型組成的，在制作模型時通常為每個子模型分別設置材質和紋理，所以這些子模型就可能使用不同的材質和紋理，因此在Direct3D程序就需要為所有的子模型分別保存材質和紋理。此外，因為每個子模型可能具有不同的材質和紋理，所以在渲染三維模型時也需要逐個子模型分別進行渲染。

渲染網格模型

網格模型接口ID3DXMesh實際上是三維物體的頂點緩沖區的集合，它將創建頂點緩沖區、定義靈活頂點格式和繪制頂點緩沖區等功能封裝在一個COM對象里，極大地方便了三維物體的繪制。對于以ID3DXMesh表示的三維物體，可以遍歷它所有的頂點緩沖區，按照相應的頂點格式將它們分別渲染，也可以直接調用它的接口函數ID3DXMesh::DrawSubset()繪制圖形，該函數的聲明如下：

Draws a subset of a mesh.

HRESULT DrawSubset(
  DWORD AttribId
);

Parameters

AttribId

[in] DWORD that specifies which subset of the mesh to draw. This value is used to differentiate faces in a mesh as belonging to one or more attribute groups.

Return Values

If the method succeeds, the return value is D3D_OK. If the method fails, the return value can be D3DERR_INVALIDCALL.

Remarks

The subset that is specified by AttribId will be rendered by the IDirect3DDevice9::DrawIndexedPrimitive method, using the D3DPT_TRIANGLELIST primitive type, so an index buffer must be properly initialized.

An attribute table is used to identify areas of the mesh that need to be drawn with different textures, render states, materials, and so on. In addition, the application can use the attribute table to hide portions of a mesh by not drawing a given attribute identifier (AttribId) when drawing the frame.

渲染網格模型的代碼如下：

void render()
{
	g_device->Clear(0, NULL, D3DCLEAR_TARGET | D3DCLEAR_ZBUFFER, D3DCOLOR_X#050505, 1.0f, 0);

	g_device->BeginScene();

	setup_world_matrix();

	for(DWORD i = 0; i < g_num_materials; i++)
	{
		g_device->SetMaterial(&g_mesh_materials[i]);
		g_device->SetTexture(0, g_mesh_textures[i]);

		g_mesh->DrawSubset(i);
	}
	

	g_device->EndScene();

	g_device->Present(NULL, NULL, NULL, NULL);
}

示例程序運行效果圖：

源程序: