The DevCaps member of D3DCAPS8 can be queried to determine the level of support for operations involving higher-order primitives. The following table lists the device capabilities related to higher-order primitives in Microsoft® DirectX® 8.1.

DirectX 8.1 supports two types of higher order primitives, or patches. These are referred to as N-Patches and Rect/Tri patches. N-Patches can be rendered using any triangle rendering call by enabling D3DRS_PATCHSEGMENTS to a value greater than 1.0. Rect/Tri patches must be rendered using the following explicit entry points.

You can use the following methods to draw patches in Microsoft® Direct3D® for DirectX.

• IDirect3DDevice8::DrawRectPatch. To better understand how the patch data is referenced in the vertex buffer, see D3DRECTPATCH_INFO.
• IDirect3DDevice8::DrawTriPatch. To better understand how the patch data is referenced in the vertex buffer, see D3DTRIPATCH_INFO.

DrawRectPatch draws a rectangular high-order patch specified by the pRectPatchInfo parameter using the currently set streams. The Handle parameter is used to associate the patch with a handle, so that the next time the patch is drawn, there is no need to respecify pRectPatchInfo. This makes it possible to precompute and cache forward difference coefficients or other information, which in turn enables subsequent calls to DrawRectPatch using the same handle to execute efficiently.

It is intended that for static patches, an application would set the vertex shader and appropriate streams, supply patch information in the pRectPatchInfo parameter, and specify a handle so that Direct3D can capture and cache information. The application can then call DrawRectPatch subsequently with pRectPatchInfo set to NULL to efficiently draw the patch. When drawing a cached patch, the currently set streams are ignored. However, it is possible to override the cached pNumSegs by specifying new values for pNumSegs. Also, it is required to set the same vertex shader when rendering a cached patch as was set when it was captured.

For dynamic patches, the patch data changes for every rendering of the patch, so it is not efficient to cache information. The application can convey this to Direct3D by setting Handle to 0. In this case, Direct3D draws the patch using the currently set streams and the pNumSegs values and does not cache any information. It is not valid to simultaneously set Handle to 0 and pPatch to NULL.

By respecifying pRectPatchInfo for the same handle, the application can overwrite the previously cached information.

If pNumSegs is set to NULL, then the tessellator uses D3DRS_PATCHSEGMENTS to control the amount of tessellation. In this case, obviously, the same tessellation is used for all sides. There are no special methods for N-patches. Tessellation is simply controlled by D3DRS_PATCHSEGMENTS. It is necessary to supply normals.

DrawTriPatch is similar to DrawRectPatch except that it draws a triangular high-order patch.

For normals, you can either directly supply them to Direct3D or have Direct3D calculate them for you. To have Direct3D generate normals for you, add D3DVSD_TESSNORMAL and D3DVSD_STREAM_TESS to your vertex declaration. D3DVSD_STREAM_TESS is a delimiter that begins the virtual stream section. One or more tokens (D3DVSD_TESSNORMAL or D3DVSD_TESSUV) can follow this delimiter. The code sample below shows the vertex declaration that you would use to have Direct3D generate normals.

DWORD decl[] =
{
   /* Vertex Data */
    D3DVSD_STREAM(0),
    D3DVSD_REG( D3DVSDE_POSITION,  D3DVSDT_FLOAT3),

    /* Data generation section implemented as a virtual stream */
    D3DVSD_STREAM_TESS(),

    /* Generate normal _using_ the position input and copy it to the normal register (output) */
    D3DVSD_TESSNORMAL( D3DVSDE_POSITION, D3DVSDE_NORMAL ),

    D3DVSD_END()
};

To have texture coordinates automatically generated, add the D3DVSD_TESSUV to your declaration after the D3DVSD_STREAM_TESS delimiter.

DWORD decl[] =
{
    /* Vertex Data */
    D3DVSD_STREAM(0),
    D3DVSD_REG( D3DVSDE_POSITION, D3DVSDT_FLOAT3),
    
    /* Data generation section implemented as a virtual stream */
    D3DVSD_STREAM_TESS(),
    
    /* Generate texture coordinates */    
    D3DVSD_TESSUV( D3DVSDE_TEXCOORD0 ),
    
    D3DVSD_END()
};