Graphics Reference
In-Depth Information
CHAPTER 7
Visible Surface Algorithms
Prerequisites:
Parts of Chapter 4 in [AgoM05], mainly Sections 4.5 and 4.7, for Section
7.10
7.1
Introduction
After modeling the geometry, the next basic step in a realistic rendering of a scene
from a given viewpoint involves determining those surface patches that will be visible
from this viewpoint. This is the
visible surface determination
problem. In the past this
was called the
hidden surface removal
problem, but the terminology is beginning to
change in order to emphasize the positive rather than the negative aspect of the
problem. Many visible surface determination algorithms have been developed over
the years. This chapter describes several well-known such algorithms. Although the
emphasis is on algorithms for linear polyhedra, we also discuss the additional com-
plexities encountered in curved object cases. The ray tracing approach to visible
surface determination, where one simply sends out rays from the camera (or eye) and
checks which surface is hit first, is treated in detail in Chapter 10.
An excellent overview of some of the very early algorithms can be found in
[SuSS74]. In general, visible surface determination algorithms can be classified as
belonging to one of three types:
object precision
,
image precision
, or
list priority
. (We
shall follow [FVFH90] and use the more descriptive term “
precision
” rather than the
older term “space,” as in “object precision algorithm” rather than “object space
algorithm”.)
Object precision algorithms are of the form
for each
object
0
in the world
do
begin
Find the part
A
of
0
that is visible;
Display
A
appropriately;
end
;
