SECTION 6.4
491
Halftones
NAME
APPEARANCE
DEFINITION
LineY
y
{ exch pop }
Round
if
|
x
| + |
y
| ≤
1
then
1
−
(x
2
+
y
2
)
else
(
|
x
| −
1)
2
+
(
|
y
| −
1)
2
−
1
{ abs exch abs
2 copy add 1 le
{ dup mul exch dup mul add 1 exch sub }
{ 1 sub dup mul exch 1 sub dup mul add 1 sub }
ifelse }
Ellipse
let w
=
(3
× |
x
|
)
+
(4
× |
y
|
)
−
3
2
y
2
x
+
⎛
---------
⎞
-
⎝
0.75
⎠
-
if w
<
0
then
1
– -----------------------------
4
2
1
–
y
2
(
1
–
x
)
+
⎛
--------------
⎞
⎝
0.75
-
⎠
else if w
>
1
then
----------------------------------------------------- –
1
4
else
0.5
−
w
{ abs exch abs 2 copy 3 mul exch 4 mul add 3 sub dup 0 lt
{ pop dup mul exch 0.75 div dup mul add
4 div 1 exch sub }
{ dup 1 gt
{ pop 1 exch sub dup mul
exch 1 exch sub 0.75 div dup mul add
4 div 1 sub }
{ 0.5 exch sub exch pop exch pop }
ifelse }
ifelse }