SECTION 4.6
317
Patterns
f
d
=0
v
a
f
d
=1
v
a
v
a
f
d
=2
v
d
One new
vertex
v
b
v
c
v
d
Three new
vertices
v
e
v
f
v
b
v
c
v
b
v
c
v
d
One new
vertex
FIGURE 4.17
Connecting triangles in a free-form Gouraud-shaded triangle mesh
Complex shapes can be created by using the edge flags to control the edge on
which subsequent triangles are formed. Figure 4.18 shows two simple examples.
Mesh 1 begins with triangle 1 and uses the following edge flags to draw each suc-
ceeding triangle:
1
(
f
a
=
f
b
=
f
c
=
0
)
2
(
f
d
=
1
)
3
(
f
e
=
1
)
4
(
f
f
=
1
)
5
(
f
g
=
1
)
6
(
f
h
=
1
)
7
(
f
i
=
2
)
8
(
f
j
=
2
)
9
(
f
k
=
2
)
10
(
f
l
=
1
)
11
(
f
m
=
1
)
Mesh 2 again begins with triangle 1 and uses the following edge flags:
1
(
f
a
=
f
b
=
f
c
=
0
)
2
(
f
d
=
1
)
3
(
f
e
=
2
)
4
(
f
f
=
2
)
5
(
f
g
=
2
)
6
(
f
h
=
2
)
The stream must provide vertex data for a whole number of triangles with appro-
priate edge flags; otherwise, an error occurs.