Graphics Reference
In-Depth Information
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Look vector
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Far clip plane
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Near clip plane
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Aspect ratio
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Figure 13.4: The distances to the near and far planes are measured along the look direction.
Far clipping
plane
Near clipping
plane
Discarded
Rendered
Clipped
Discarded
Figure 13.5: Objects outside the view frustum will not be rendered.
It is not only the utility of being able to set the near- and far-plane distances
that motivates their use, as you'll see presently; they also allow a rasterizing ren-
derer to avoid certain floating-point-comparison problems that generate errors in
images.
Clipping planes have often been used in games to help reduce rendering time
by removing distant objects, but sometimes as you move forward in a game, a dis-
tant object will “pop” into view, which can be distracting. The general solution to
this problem was to render objects in the distance as being obscured by fog so that
they appeared gradually as you approached them. In more modern games, we have
better rendering systems, and many objects are represented with multiple different
levels of detail (see Section 25.4) so that when they are distant, they can be ren-
dered with fewer polygons, making the use of fog less common than it once was.
a View Specification
We'll now convert from a view specification to some specific geometry. From a
specification, we'll build (a) an orthonormal coordinate system based at the cam-
era position, and (b) several points on the view cone, as shown in Figure 13.6.
We'll use these in building the transformations we need. Having a coordinate
frame based at the camera is very convenient, since we'll later be transform-
ing the camera to the origin and aligning its coordinate frame with the standard
xyz
-coordinate system at the origin.
