AMD Typewriter x86 사용자 설명서

22007E/0—November 1999

Clipping is one of the major activities occurring in a 3D
graphics pipeline. In many instances, this activity is split into
two parts which do not necessarily have to occur consecutively:

■

Computation of the clip code for each vertex, where each
bit of the clip code indicates whether the vertex is outside
the frustum with regard to a specific clip plane.

■

Examination of the clip code for a vertex and clipping if the
clip code is non-zero.

The following example shows how to use 3DNow! instructions to
efficiently implement a clip code computation for a frustum
that is defined by: 

■

-w <= x <= w

■

-w <= y <= w

■

-w <= z <= w

.DATA

RIGHT   EQU 01h
LEFT    EQU 02h
ABOVE   EQU 04h
BELOW   EQU 08h
BEHIND  EQU 10h
BEFORE  EQU 20h

               ALIGN 8

ABOVE_RIGHT    DD   RIGHT
               DD   ABOVE
BELOW_LEFT     DD   LEFT
               DD   BELOW
BEHIND_BEFORE  DD   BEFORE
               DD   BEHIND

.CODE

;; Generalized computation of 3D clip code (out code)
;;
;; Register usage: IN        MM5   y | x
;;                           MM6   w | z
;;                           
;;                 OUT       MM2   clip code (out code)