Outcode-type testing (cohen-sutherland clipping) could be used to
determine completely clipped or unclipped polygons ahead of time,
avoiding the need to clip and copy entirely for such polygons.
Outcode-type tests work best in viewspace, with the frustum
normalized so that the field of view is 90 degrees, so simple
compares, rather than dot products, can be used to categorize
points with respect to the frustum.

 0110 | 0100 | 1100
------+------+------
 0010 | 0000 | 1000
------+------+------
 0011 | 0001 | 1001

See
Computer Graphics  by Foley & van Dam
Procedural Elements of Computer Graphics by Rogers
