| Microsoft DirectX 8.1 (C++) |
Your Microsoft® Direct3D® application can assign texture coordinates to any vertex of any primitive. For details, see Texture Coordinates. Typically, the u- and v-texture coordinates that you assign to a vertex are in the range of 0.0 to 1.0 inclusive. However, by assigning texture coordinates outside that range, you can create certain special texturing effects.
You control what Direct3D does with texture coordinates that are outside the [0.0, 1.0] range by setting the texture addressing mode. For instance, you can have your application set the texture addressing mode so that a texture is tiled across a primitive. The following topics contain additional details.
Direct3D enables applications to perform texture wrapping. It is important to note that setting the texture addressing mode to D3DTADDRESS_WRAP is not the same as performing texture wrapping. Setting the texture addressing mode to D3DTADDRESS_WRAP results in multiple copies of the source texture being applied to the current primitive, and enabling texture wrapping changes how the system rasterizes textured polygons. For details, see Texture Wrapping.
Enabling texture wrapping effectively makes texture coordinates outside the [0.0, 1.0] range invalid, and the behavior for rasterizing such delinquent texture coordinates is undefined in this case. When texture wrapping is enabled, texture addressing modes are not used. Take care that your application does not specify texture coordinates lower than 0.0 or higher than 1.0 when texture wrapping is enabled.
You can set texture addressing modes for individual texture stages by calling the IDirect3DDevice8::SetTextureStageState method. Specify the desired texture stage identifier in the first parameter. Set the second parameter to D3DTSS_ADDRESSU, D3DTSS_ADDRESSV, or D3DTSS_ADDRESSW values to update the u-, v-, or w-addressing modes individually. The third parameter you pass to SetTextureStageState determines which mode is being set. This can be any member of the D3DTEXTUREADDRESS enumerated type. To retrieve the current texture address mode for a texture stage, call IDirect3DDevice8::GetTextureStageState, using the D3DTSS_ADDRESSU, D3DTSS_ADDRESSV, or D3DTSS_ADDRESSW members of the D3DTEXTURESTAGESTATETYPE enumeration to identify the address mode about which you want information.
Although the system generally allows texture coordinates outside the range of 0.0 and 1.0, inclusive, hardware limitations often affect how far outside that range texture coordinates can be. A rendering device communicates this limit in the MaxTextureRepeat member of the D3DCAPS8 structure when you retrieve device capabilities. The value in this member describes the full range of texture coordinates allowed by the device. For instance, if this value is 128, then the input texture coordinates must be kept in the range -128.0 to +128.0. Passing vertices with texture coordinates outside this range is invalid. The same restriction applies to the texture coordinates generated as a result of automatic texture coordinate generation and texture coordinate transformations.
The interpretation of MaxTextureRepeat is also affected by the D3DPTEXTURECAPS_TEXREPEATNOTSCALEDBYSIZE capability bit. When this bit is set, the value in the MaxTextureRepeat member of D3DCAPS8 is used precisely as described. However, when D3DPTEXTURECAPS_TEXREPEATNOTSCALEDBYSIZE is not set, texture repeating limitations depend on the size of the texture indexed by the texture coordinates. In this case, MaxTextureRepeat must be scaled by the current texture size at the largest level of detail to compute the valid texture coordinate range. For example, given a texture dimension of 32 and MaxTextureRepeat value of 512, the actual valid texture coordinate range is 512/32 = 16, so the texture coordinates for this device must be within the range of -16.0 to +16.0.
Additional information on the texture addressing modes is contained in the following topics.