CHAPTER 4
320
Graphics
TABLE 4.33 Additional entries specific to a type 5 shading dictionary
KEY
TYPE
VALUE
BitsPerCoordinate
integer
integer
integer
(Required)
The number of bits used to represent each vertex coordinate.
Valid values are 1, 2, 4, 8, 12, 16, 24, and 32.
(Required)
The number of bits used to represent each color component.
Valid values are 1, 2, 4, 8, 12, and 16.
(Required)
The number of vertices in each row of the lattice; the value
must be greater than or equal to 2. The number of rows need not be
specified.
(Required)
An array of numbers specifying how to map vertex coordinates
and color components into the appropriate ranges of values. The decoding
method is similar to that used in image dictionaries (see “Decode Arrays”
[
x
min
x
max
y
min
y
max
c
1,min
c
1,max
…
c
n,min
c
n,max
]
BitsPerComponent
VerticesPerRow
Decode
array
Note that only one pair of
c
values should be specified if a
Function
entry
is present.
Function
function
(Optional)
A 1-in,
n-out
function or an array of
n
1-in, 1-out functions
(where
n
is the number of color components in the shading dictionary’s
color space). If this entry is present, the color data for each vertex must be
specified by a single parametric variable rather than by
n
separate color
components. The designated function(s) are called with each interpolated
value of the parametric variable to determine the actual color at each
point. Each input value is forced into the range interval specified for the
corresponding color component in the shading dictionary’s
Decode
array.
Each function’s domain must be a superset of that interval. If the value re-
turned by the function for a given color component is out of range, it is
adjusted to the nearest valid value.
This entry cannot be used with an
Indexed
color space.
All vertex coordinates are expressed in the shading’s target coordinate space. If
the shading dictionary includes a
Function
entry, only a single parametric value,
t,
is permitted for each vertex in place of the color components
c
1
…
c
n
.
The
VerticesPerRow
entry in the shading dictionary gives the number of vertices
in each row of the lattice. All of the vertices in a row are specified sequentially,
followed by those for the next row. Given
m
rows of
k
vertices each, the triangles