Graphics Reference
In-Depth Information
have uniform depth complexity in all directions, the problem of high depth com-
plexity can be alleviated by rendering the objects along different view directions from
pass to pass. A simple alternative is to alternate between viewing down the three
principal axes in a cyclic fashion. High depth complexity along one but not all axes is
thus effectively handled. Although problem configurations are still possible, they are
unlikely to occur in practice.
Figure 10.6 illustrates the algorithm on the set of objects
S
. In the
first pass of the filtering algorithm, objects are rendered in order
A
through
H
. After
the first pass, objects
A
,
B
,
C
,
D
,
G
, and
H
have been marked fully visible (Figure
10.6a). In the second pass, objects are rendered in order
H
through
A
. At the end of
the second pass, objects
H
,
G
,
F
, and
B
have been marked fully visible (Figure 10.6b).
After the first round (of two passes), objects
B
,
G
, and
H
have been marked fully
visible in both passes. These three objects can therefore safely be pruned from the
PCS (Figure 10.6c). If a second round of filtering is performed, object
C
can be culled
after the two passes. The remaining set of four objects (
A
,
D
,
E
, and
F
) cannot be
pruned further using the same view axis. However, if a horizontal view axis is used
object
E
can be pruned as well, ultimately leaving objects
A
,
D
, and
F
in the PCS (and
thus as conservatively colliding).
The filtering algorithm can be applied directly to the objects (whether convex or
concave). If the objects are of high complexity, it may be better to filter the objects
={
A
,
B
,
...
,
H
}
First pass (A-H):
Far
E
C
H
A
D
B
G
F
Near
(a)
Second pass (H-A):
Far
E
C
H
A
D
B
G
F
Near
(b)
Pruned objects:
Far
E
C
H
A
D
B
G
F
Near
(c)
Figure 10.6
Objects, shown in gray, are those considered fully visible in (a) the first and
(b) the second pass. (c) Objects
B
,
G
, and
H
are fully visible in both passes and can be pruned
from the PCS.
