Primitive Clipping State

Primitives that lie partially inside (or completely outside) the view frustum can be clipped so that only the visible portion of the primitive will be rendered. Clipping reduces the amount of work that is done to only those primitives or portions of a primitive that will be visible.

To use the pipeline for clipping, set the D3DRS_CLIPPING render state to TRUE (the default value) to enable clipping, or to FALSE to disable Direct3D clipping.