Texture Coordinate Formats

Texture coordinates in Microsoft® Direct3D® can include one, two, three, or four floating point elements to address textures with varying levels of dimension. A 1-D texture — a texture surface with dimensions of 1-by-n texels — is addressed by one texture coordinate. The most common case, 2-D textures, are addressed with two texture coordinates commonly called u and v.

As described in About Vertex Formats, 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 flexible vertex format flags 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 are not 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 code example shows 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, 2-D
    float     t;      // 2nd set, 1-D
} CustomVertexFormat;

Note   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 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^th) element. For more information, see Texture Coordinate Transformations.

See Also

Texture Coordinates

 Last updated on Thursday, April 08, 2004

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