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Texture Coordinate Formats (Direct3D 9)

Texture coordinates in Direct3D can include one, two, three, or four floating point elements to address textures with varying levels of dimension. A 1D texture - a texture surface with dimensions of 1-by-n texels - is addressed by one texture coordinate. The most common case, 2D textures, are addressed with two texture coordinates commonly called u and v. Direct3D supports two types of 3D textures, cubic-environment maps and volume textures. Cubic environment maps aren't truly 3D, but they are addressed with a 3-element vector. For details, see Cubic Environment Mapping (Direct3D 9).

As described in Fixed Function FVF Codes (Direct3D 9), applications encode texture coordinates in the vertex format. The vertex format can include multiple sets of texture coordinates. Use the D3DFVF_TEX0 through D3DFVF_TEX8 D3DFVF to describe a vertex format that includes no texture coordinates, or as many as eight sets.

Each texture coordinate set can have between one and four elements. The D3DFVF_TEXTUREFORMAT1 through D3DFVF_TEXTUREFORMAT4 flags describe the number of elements in a texture coordinate in a set, but these flags aren't used by themselves. Rather, the D3DFVF_TEXCOORDSIZEN set of macros use these flags to create bit patterns that describe the number of elements used by a particular set of texture coordinates in the vertex format. These macros accept a single parameter that identifies the index of the coordinate set whose number of elements is being defined. The following example illustrates how these macros are used.



// This vertex format contains two sets of texture coordinates.
// The first set (index 0) has 2 elements, and the second set 
// has 1 element. The description for this vertex format would be: 
//     dwFVF = D3DFVF_XYZ  | D3DFVF_NORMAL | D3DFVF_DIFFUSE | D3DFVF_TEX2 |
//             D3DFVF_TEXCOORDSIZE2(0) | D3DFVF_TEXCOORDSIZE1(1); 
//
typedef struct CVF
{
	D3DVECTOR position;
	D3DVECTOR normal;
	D3DCOLOR  diffuse;
	float     u, v;   // 1st set, 2D
	float     t;      // 2nd set, 1D
} CustomVertexFormat;


Note  With the exception of cubic-environment maps and volume textures, rasterizers cannot address textures by using any more than two elements. Applications can supply up to three elements for a texture coordinate, but only if the texture is a cube map, a volume texture, or the D3DTTFF_PROJECTED texture transform flag is used. The D3DTTFF_PROJECTED flag causes the rasterizer to divide the first two elements by the third (or n) element. For more information, see Texture Coordinate Transformations (Direct3D 9).

 

 

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