Microsoft® Direct3D® applications can define model vertices in several different ways. Support for flexible vertex definitions, also known as flexible vertex formats or flexible vertex format codes, makes it possible for your application to use only the vertex components it needs, eliminating those components that aren't used. By using only the needed vertex components, your application can conserve memory and minimize the processing bandwidth required to render models. You describe how your vertices are formatted by using a combination of Flexible Vertex Format Flags.

The Direct3DDevice8 Microsoft® Visual Basic® class includes methods that accept a combination of these flags, and uses them to determine how to render primitives. Basically, these flags tell the system which vertex components—position, vertex blending weights, normal, colors, the number and format of texture coordinates—your application uses and, indirectly, which parts of the rendering pipeline you want Direct3D to apply to them. In addition, the presence or absence of a particular vertex format flag communicates to the system which vertex component fields are present in memory and which you've omitted.

To determine device limitations, you can query a device for the D3DFVFCAPS_DONOTSTRIPELEMENTS and D3DFVFCAPS_TEXCOORDCOUNTMASK flexible vertex format flags. For more information, see the FVFCaps member of the D3DCAPS8 structure.

Texture coordinates can be declared in different formats, allowing textures to be addressed using as few as one coordinate, or as many as four texture coordinates for 2-D projected texture coordinates. Use the D3DFVF_TEXCOORDSIZEn set of helper functions from Math.bas to create bit patterns that identify the texture coordinate formats that your vertex format uses. The Math.bas Visual Basic code module is included with this SDK.

No real application will use every single component—the reciprocal homogeneous W (RHW) and vertex normal fields are mutually exclusive. Nor will most applications try to use all eight sets of texture coordinates, but the flexibility is there. There are several restrictions on which flags you can use with other flags. These are mostly common sense. For example, you cannot use the D3DFVF_XYZ and D3DFVF_XYZRHW flags together, as this would indicate that your application is describing a vertex's position with both untransformed and transformed vertices.

To use indexed vertex blending, the D3DFVF_LASTBETA_UBYTE4 flag should appear at the end of the FVF. The presence of this flag indicates that the fifth blending weight will be treated as a DWORD instead of float. For more information, see Indexed Vertex Blending.

The following code samples shows the difference between an FVF code that uses the D3DFVF_LASTBETA_UBYTE4 flag and one that doesn't. The FVF defined below does not use the D3DFVF_LASTBETA_UBYTE4 flag. The flag D3DFVF_XYZ3 is present when four blending indices are used because you always use (1 - the sum of the first three) for the fourth.

Const D3DFVF_BLENDVERTEX = (D3DFVF_XYZB3 Or D3DFVF_NORMAL Or D3DFVF_TEX1)

Private Type BLENDVERTEX
    v As D3DXVECTOR  ' Referenced as v0 in the vertex shader
    blend1 As Single ' Referenced as v1.x in the vertex shader
    blend2 As Single ' Referenced as v1.y in the vertex shader
    blend3 As Single ' Referenced as v1.z in the vertex shader
                     ' v1.w = 1.0 - (v1.x + v1.y + v1.z)
    n As D3DXVECTOR  ' Referenced as v3 in the vertex shader
    tu as Single     ' tu and tv referenced as v7 in the vertex shader
    tv As Single     '
End Type

The FVF defined below uses the D3DFVF_LAST_UBYTE4 flag.

Const D3DFVF_BLENDVERTEX = (D3DFVF_XYZB4 Or D3DFVF_LASTBETA_UBYTE4 Or _
                            D3DFVF_NORMAL Or D3DFVF_TEX1)
Private Type BLENDVERTEX
    v As D3DXVECTOR    'Referenced as v0 in the vertex shader
    blend1 As Single   ' Referenced as v1.x in the vertex shader
    blend2 As Single   ' Referenced as v1.y in the vertex shader
    blend3 As Single   ' Referenced as v1.z in the vertex shader
                       ' v1.w = 1.0 - (v1.x + v1.y + v1.z)
    indices As Long    ' Referenced as v2.xyzw in the vertex shader 
    n As D3DXVECTOR    ' Referenced as v3 in the vertex shader
    tu As Single       ' tu and tv referenced as v7 in the vertex shader
    tv As Single
End Type