對(duì)一些特殊的應(yīng)用需要對(duì)紋理坐標(biāo)進(jìn)行處理，主要包括紋理坐標(biāo)自動(dòng)生成和紋理坐標(biāo)變換。下圖顯示了紋理坐標(biāo)的來(lái)源、處理過(guò)程以及到達(dá)光柵處理器的過(guò)程。

紋理坐標(biāo)自動(dòng)生成

在Direct3D程序中，不僅可以在模型載入階段或渲染階段指定物體的紋理坐標(biāo)，還可以通過(guò)Direct3D渲染引擎自動(dòng)生成紋理坐標(biāo)，用于諸如環(huán)境映射等特殊的視覺效果。與手動(dòng)設(shè)置紋理坐標(biāo)相比，紋理坐標(biāo)自動(dòng)生成在Direct3D坐標(biāo) 變換和光照流水線中完成，執(zhí)行速度更快。

Direct3D系統(tǒng)可以使用經(jīng)過(guò)變換的攝像機(jī)空間頂點(diǎn)位置坐標(biāo)、法線信息來(lái)生成紋理坐標(biāo)。如果使用紋理坐標(biāo)自動(dòng)生成，那么在頂點(diǎn)中就可以不用包含紋理坐標(biāo)數(shù)據(jù)，從而可以降低圖形渲染時(shí)的數(shù)據(jù)傳輸量。紋理坐標(biāo)自動(dòng)生成主要用于產(chǎn)生一些特殊效果，在大多數(shù)情況下還是手工為每個(gè)頂點(diǎn)指定紋理坐標(biāo)。

通過(guò)調(diào)用SetTextureStageState()并將第二個(gè)參數(shù)設(shè)置為D3DTSS_TEXCOORDINDEX來(lái)控制Direct3D系統(tǒng)如何自動(dòng)生成紋理坐標(biāo)。

D3DTSS_TEXCOORDINDEX

Index of the texture coordinate set to use with this texture stage. You can specify up to eight sets of texture coordinates per vertex. If a vertex does not include a set of texture coordinates at the specified index, the system defaults to the u and v coordinates (0,0).

When rendering using vertex shaders, each stage's texture coordinate index must be set to its default value. The default index for each stage is equal to the stage index. Set this state to the zero-based index of the coordinate set for each vertex that this texture stage uses.

Additionally, applications can include, as logical OR with the index being set, one of the constants to request that Direct3D automatically generate the input texture coordinates for a texture transformation. For a list of all the constants, see D3DTSS_TCI.

With the exception of D3DTSS_TCI_PASSTHRU, which resolves to zero, if any of the following values is included with the index being set, the system uses the index strictly to determine texture wrapping mode. These flags are most useful when performing environment mapping.

其中第三個(gè)參數(shù)可以設(shè)為下列列表中的成員：

D3DTSS_TCI

Driver texture coordinate capability flags.

These constants are used by D3DTSS_TEXCOORDINDEX.

D3DTSS_TEXCOORDINDEX用于指定特定紋理層使用頂點(diǎn)中的第幾組紋理坐標(biāo)，但如果指定了上表中的成員值，Direct3D將忽略頂點(diǎn)中的紋理坐標(biāo)，轉(zhuǎn)而使用自動(dòng)生成的紋理坐標(biāo)。

D3DTSS_TEXTURETRANSFORMFLAGS用來(lái)控制生成的紋理坐標(biāo)的輸出，在大多數(shù)情況下紋理坐標(biāo)是二維的，即將D3DTSS_TEXTURETRANSFORMFLAGS設(shè)置為D3DTTFF_COUNT2。但當(dāng)繪制線段或三維紋理時(shí)，紋理坐標(biāo)可能是一維或三維的。

D3DTSS_TEXTURETRANSFORMFLAGS

Member of the D3DTEXTURETRANSFORMFLAGS enumerated type that controls the transformation of texture coordinates for this texture stage. The default value is D3DTTFF_DISABLE.

輸出的紋理坐標(biāo)維數(shù)由枚舉類型D3DTSS_TEXTURETRANSFORMFLAGS指定，其定義如下：

Defines texture coordinate transformation values.

typedef enum D3DTEXTURETRANSFORMFLAGS
{
    D3DTTFF_DISABLE = 0,
    D3DTTFF_COUNT1 = 1,
    D3DTTFF_COUNT2 = 2,
    D3DTTFF_COUNT3 = 3,
    D3DTTFF_COUNT4 = 4,
    D3DTTFF_PROJECTED = 256,
    D3DTTFF_FORCE_DWORD = 0x7fffffff,
} D3DTEXTURETRANSFORMFLAGS, *LPD3DTEXTURETRANSFORMFLAGS;

Constants

D3DTTFF_DISABLE

Texture coordinates are passed directly to the rasterizer.

D3DTTFF_COUNT1

The rasterizer should expect 1D texture coordinates. This value is used by fixed function vertex processing; it should be set to 0 when using a programmable vertex shader.

D3DTTFF_COUNT2

The rasterizer should expect 2D texture coordinates. This value is used by fixed function vertex processing; it should be set to 0 when using a programmable vertex shader.

D3DTTFF_COUNT3

The rasterizer should expect 3D texture coordinates. This value is used by fixed function vertex processing; it should be set to 0 when using a programmable vertex shader.

D3DTTFF_COUNT4

The rasterizer should expect 4D texture coordinates. This value is used by fixed function vertex processing; it should be set to 0 when using a programmable vertex shader.

D3DTTFF_PROJECTED

This flag is honored by the fixed function pixel pipeline, as well as the programmable pixel pipeline in versions ps_1_1 to ps_1_3. When texture projection is enabled for a texture stage, all four floating point values must be written to the corresponding texture register. Each texture coordinate is divided by the last element before being passed to the rasterizer. For example, if this flag is specified with the D3DTTFF_COUNT3 flag, the first and second texture coordinates are divided by the third coordinate before being passed to the rasterizer.

D3DTTFF_FORCE_DWORD

Forces this enumeration to compile to 32 bits in size. Without this value, some compilers would allow this enumeration to compile to a size other than 32 bits. This value is not used.

Remarks

Texture coordinates can be transformed using a 4 x 4 matrix before the results are passed to the rasterizer. The texture coordinate transforms are set by calling IDirect3DDevice9::SetTextureStageState, and by passing in the D3DTSS_TEXTURETRANSFORMFLAGS texture stage state and one of the values from D3DTEXTURETRANSFORMFLAGS. For more information about texture transforms, see Texture Coordinate Transformations (Direct3D 9).

首先，我們定義頂點(diǎn)結(jié)構(gòu)和格式：

struct sCustomVertex
{
	float x, y, z;
};

#define D3DFVF_CUSTOM_VERTEX	D3DFVF_XYZ

接著生成頂點(diǎn)數(shù)據(jù)，頂點(diǎn)數(shù)據(jù)中沒有包含紋理坐標(biāo)：

// create vertex buffer and fill data

sCustomVertex vertices[] = 	
{
    { -1.0f, -1.0f,  0.0f},
    { -1.0f,  1.0f,  0.0f},
    {  1.0f, -1.0f,  0.0f},
    {  1.0f,  1.0f,  0.0f}
};

pd3dDevice->CreateVertexBuffer(sizeof(vertices), 0, D3DFVF_CUSTOM_VERTEX, D3DPOOL_MANAGED, &g_vertex_buffer, NULL);

void* ptr;
g_vertex_buffer->Lock(0, sizeof(vertices), (void**)&ptr, 0);
memcpy(ptr, vertices, sizeof(vertices));
g_vertex_buffer->Unlock();

然后讓Direct3D自動(dòng)生成紋理坐標(biāo)：

// create texture coordinate using vertex position in camera space
pd3dDevice->SetTextureStageState(0, D3DTSS_TEXCOORDINDEX, D3DTSS_TCI_CAMERASPACEPOSITION);
pd3dDevice->SetTextureStageState(0, D3DTSS_TEXTURETRANSFORMFLAGS, D3DTTFF_COUNT2);

運(yùn)行效果：

若設(shè)置D3DTSS_TEXCOORDINDEX為以下D3DTSS_TCI_CAMERASPACEREFLECTIONVECTOR，則效果為：

若設(shè)置D3DTSS_TEXCOORDINDEX為以下D3DTSS_TCI_SPHEREMAP，則效果為：

主程序：

下載示例工程