Graphics Reference
In-Depth Information
Figure 14.10.
The viewing frustum.
gular width of the view frustum is defined by an aspect ratio. Once again, only
objects inside this visible volume can participate in the rendering process.
Y
Recall that the aspect ratio describes the width-to-height ratio of the drawing
area, or,
n tan(α)
Z
α
W
dc
H
dc
.
As illustrated by Figure 14.11, with half of the vertical field-of-view angle being
α
n
aspect ratio
=
Origin (0,0)
, then, at a distance of
n
, the height of the near plane is
Figure 14.11.
Near
plane height.
n
h
=
2
n
tan
(
α
)
.
In the same way, the width of the near plane is
n
w
=
2
n
tan
(
β
)
,
where
is half of the horizontal field-of-view angle. To maintain proper aspect
ratio (so that spheres will appear round), the graphics API ensures that
β
n
n
h
aspect ratio
=
2
n
tan
(
β
)
2
n
tan
(
α
)
=
tan
(
β
)
tan
(
α
)
,
=
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