| Microsoft DirectX 8.1 (Visual Basic) |
The system can use the transformed camera-space position or the normal from a vertex as texture coordinates, or it can compute the three element vectors used to address a cubic environment map. Like texture coordinates that you explicitly specify in a vertex, you can use automatically generated texture coordinates as input for texture coordinate transformations.
Automatically generated texture coordinates can significantly reduce the bandwidth required for geometry data by eliminating the need for explicit texture coordinates in the vertex format. In many cases, the texture coordinates that the system generates can be used with transformations to produce special effects. Of course, this is a special-purpose feature, and you will use explicit texture coordinates for many occasions.
In Microsoft® Visual Basic®, the D3DTSS_TEXCOORDINDEX texture-stage state (from the CONST_D3DTEXTURESTAGESTATETYPE enumeration) controls how the system generates texture coordinates.
Normally, this state instructs the system to use a particular set of texture coordinates encoded in the vertex format. When you include the D3DTSS_TCI_CAMERASPACENORMAL, D3DTSS_TCI_CAMERASPACEPOSITION, or D3DTSS_TCI_CAMERASPACEREFLECTIONVECTOR flags in the value that you assign to this state, the system behavior is quite different. If any of these flags are present, the texture stage ignores the texture coordinates within the vertex format in favor of coordinates that the system generates. The meanings for each flag are shown in the following list.
The preceding flags are mutually exclusive. If you include one flag, you can still specify an index value, which the system uses to determine the texture wrapping mode.
The following code example shows how these flags are used in Visual Basic.
'
' For this example, the D3DDevice variable is a valid
' reference to a Direct3DDevice8 object.
'
' Use the vertex position (camera-space) as the input
' texture coordinates for this texture stage, and the
' wrap mode set in the D3DRENDERSTATE_WRAP1 render state.
'
Call D3DDevice.SetTextureStageState( 0, D3DTSS_TEXCOORDINDEX, _
D3DTSS_TCI_CAMERASPACEPOSITION Or 1 )
Note Automatically generated texture coordinates are most useful as input values for a texture coordinate transformation, or to eliminate the need for your application to compute three-element vectors for cubic-environment maps.
Texture Coordinate Transformations, Cubic Environment Mapping