491
SECTION 6.4 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
y 2
x + ⎛ ---------⎞
2
-
⎝ 0.75⎠
if w < 0 then 1 – -----------------------------
-
4
1– y 2
( 1 – x ) + ⎛ -------------- ⎞
2
⎝ 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 }