You can use triangle strips and triangle fans to specify an entire surface without having to provide all three vertices for each of the triangles. For example, only seven vertices are required to define the following triangle strip.
The system uses vertices v0, v1, and v2 to draw the first triangle, v1, v3, and v2 to draw the second triangle, v3, v4, and v2 to draw the third, and so on. Notice that the vertices of the second triangle are out of order; this is required to make sure that all of the triangles are drawn in a clockwise orientation.
A triangle fan is similar to a triangle strip, except that all of the triangles share one vertex.
The system uses vertices v0, v1, and v2 to draw the first triangle, v0, v2, and v3 to draw the second triangle, and so on.
You can use the wFlags member of the D3DTRIANGLE structure to specify the flags that build triangle strips and fans.