SECTION 4.6
319
Patterns
Type 5 Shadings (Lattice-Form Gouraud-Shaded Triangle Meshes)
Type 5 shadings (lattice-form Gouraud-shaded triangle meshes) are similar to
type 4, but instead of using free-form geometry, their vertices are arranged in a
pseudorectangular lattice,
which is topologically equivalent to a rectangular grid.
The vertices are organized into rows, which need not be geometrically linear (see
(i,
j)
(i,
j+1)
(i+1,
j)
(i+1,
j+1)
Ideal lattice
Pseudorectangular lattice
FIGURE 4.19
Lattice-form triangle meshes
addition to those common to all shading dictionaries (Table 4.28) and stream dic-
tionaries (Table 3.4 on page 62).
The data stream for a type 5 shading has the same format as for type 4, except that
type 5 does not use edge flags to define the geometry of the triangle mesh. The
data for each vertex thus consists of the following values, in the order shown:
x y c
1
…
c
n
where
x
and
y
are the vertex’s horizontal and vertical coordinates
c
1
…
c
n
are its color components