The wFlags member of the D3DTRIANGLE structure includes flags that allow the system to reuse vertices when building triangle strips and fans. Effective use of these flags allows some hardware to run much faster than it would otherwise.
Applications can use these flags in two ways as acceleration hints to the driver.
| D3DTRIFLAG_STARTFLAT(len) | |
| If the current triangle is culled, the driver can also cull the number of subsequent triangles given by len in the strip or fan. | |
| D3DTRIFLAG_ODD and D3DTRIFLAG_EVEN | |
| The driver needs to reload only one new vertex from the triangle and it can reuse the other two vertices from the last triangle that was rendered. | |
The best possible performance occurs when an application uses both the D3DTRIFLAG_STARTFLAT flag and the D3DTRIFLAG_ODD and D3DTRIFLAG_EVEN flags.
Because some drivers might not check the D3DTRIFLAG_STARTFLAT flag, applications must be careful when using it. An application using a driver that doesn't check this flag might not render polygons that should have been rendered.
Applications must use the D3DTRIFLAG_START flag before using the D3DTRIFLAG_ODD and D3DTRIFLAG_EVEN flags. D3DTRIFLAG_START causes the driver to reload all three vertices. All triangles following the D3DTRIFLAG_START flag can use the D3DTRIFLAG_ODD and D3DTRIFLAG_EVEN flags indefinitely, providing the triangles share edges.
The debugging version of this Programmer's Reference validates the D3DTRIFLAG_ODD and D3DTRIFLAG_EVEN flags.
For more information, see Triangle Strips and Fans.