
72 Chapter 2 The Graphics System
p
i
2
> 0
p
i
2
≤ 0
p
i
0
> 0
V
i
l
V
i
l
V
c
0
V
c
0
V
i
0
V
i
0
V
i
0
V
i
0
V
i
2
V
i
2
V
c
l
V
c
l
V
c
l
V
c
l
p
i
0
≤ 0
V
c
0
V
c
0
V
i
l
V
i
l
V
i
2
V
i
2
Figure 2.25 Four configurations for triangle splitting. Only the triangles in the shaded region are
important, so the quadrilaterals outside are not split. The subscript c indicates clip
vertices.
The splitting of a triangle by a frustum plane is accomplished by computing the
intersection of the triangle edges with the plane. The three vertices of the triangle are
tested for inclusion in the frustum. If the frustum plane is N
.
X = d and if the vertices
of the triangle are V
i
for 0 ≤i ≤2, then the edge with endpoints V
i
0
and V
i
1
intersects ...