SECTION 4.6
311
Patterns
Note:
This type of shading cannot be used with an
Indexed
color space.
TABLE 4.31 Additional entries specific to a type 3 shading dictionary
KEY
TYPE
VALUE
Coords
array
(Required)
An array of six numbers
[
x
0
y
0
r
0
x
1
y
1
r
1
]
specifying the centers and
radii of the starting and ending circles, expressed in the shading’s target coor-
dinate space. The radii
r
0
and
r
1
must both be greater than or equal to 0. If one
radius is 0, the corresponding circle is treated as a point; if both are 0, nothing is
painted.
(Optional)
An array of two numbers
[
t
0
t
1
]
specifying the limiting values of a
parametric variable
t.
The variable is considered to vary linearly between these
two values as the color gradient varies between the starting and ending circles.
The variable
t
becomes the input argument to the color function(s). Default
value:
[ 0.0 1.0 ]
.
(Required)
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). The
function(s) are called with values of the parametric variable
t
in the domain de-
fined by the shading dictionary’s
Domain
entry. Each function’s domain must be
a superset of that of the shading dictionary. If the value returned by the function
for a given color component is out of range, it is adjusted to the nearest valid val-
ue.
(Optional)
An array of two boolean values specifying whether to extend the
shading beyond the starting and ending circles, respectively. Default value:
[ false false ]
.
Domain
array
Function
function
Extend
array
The color blend is based on a family of
blend circles
interpolated between the
starting and ending circles that are defined by the shading dictionary’s
Coords
entry. The blend circles are defined in terms of a subsidiary parametric variable
t
–
t
0
--------------
-
s
=
t
1
–
t
0