Only the primitives which are within the visual volume need to actually be rastered (drawn). This visual volume is defined as the inside of a frustum, a shape in the form of a pyramid with a cut off top. Primitives which are completely outside the visual volume are discarded; This is called frustum culling. Further culling methods such as backface culling, which reduce the number of primitives to be considered, can theoretically be executed in any step of the graphics pipeline. Primitives which are only partially inside the cube must be clipped against the cube. The advantage of the previous projection step is that the clipping always takes place against the same cube. Only the - possibly clipped - primitives, which are within the visual volume, are forwarded to the final step.