CHAPTER 7
536
Transparency
f
s
=
f
j
×
f
m
×
f
k
i
i
i
i
α
s
=
α
j
× (
f
m
×
q
m
) × (
f
k
×
q
k
)
i
i
i
i
i
i
f
g
=
Union
(
f
g
,
f
s
)
i
i
–
1
i
α
g
=
Union
(
α
g
,
α
s
)
α
i
=
Union
(
α
0
,
α
g
)
i
i
i
–
1
i
α
s
⎛
α
s
i
⎞
C
i
=
⎜
1
– ------
⎟
×
C
i
–
1
+ ------
i
× ( (
1
–
α
i
–
1
) ×
C
s
+
α
i
–
1
×
B
i
(
C
i
–
1
,
C
s
)
)
-
-
α
i
⎠
α
i
i
i
⎝
•
Result:
⎛
α
0
⎞
C
=
C
n
+
(
C
n
–
C
0
) ×
⎜
------- –
α
0
⎟
-
⎝
α
g
n
⎠
f
=
f
g
α
=
α
g
n
where the variables have the meanings shown in Table 7.8 (in addition to those in
For an element
E
i
that is an elementary object, the color, shape, and alpha
values
C
s
,
f
j
, and
α
j
are intrinsic attributes of the object. For an element that is
i
i
i
a group, the group compositing function is applied recursively to the subgroup
and the resulting
C, f,
and
α
values are used for its
C
s
,
f
j
, and
α
j
in the calcula-
i
i
i
tions for the parent group.
TABLE 7.8 Variables used in the group compositing formulas
VARIABLE
MEANING
n
E
i
Element
i
of the group: a compound variable representing the ele-
ment’s color, shape, opacity, and blend mode
Source shape for element
E
i
Object shape for element
E
i
Mask shape for element
E
i
f
s
f
j
i
i
f
m
i