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<STRONG>NAME</STRONG>
<STRONG>gluPerspective</STRONG> - set up a perspective projection matrix
<STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>
void <STRONG>gluPerspective</STRONG>( GLdouble <EM>fovy</EM>,
GLdouble <EM>aspect</EM>,
GLdouble <EM>zNear</EM>,
GLdouble <EM>zFar</EM> )
<STRONG>PARAMETERS</STRONG>
<EM>fovy</EM> Specifies the field of view angle, in degrees, in
the <EM>y</EM> direction.
<EM>aspect</EM> Specifies the aspect ratio that determines the field
of view in the <EM>x</EM> direction. The aspect ratio is the
ratio of <EM>x</EM> (width) to <EM>y</EM> (height).
<EM>zNear</EM> Specifies the distance from the viewer to the near
clipping plane (always positive).
<EM>zFar</EM> Specifies the distance from the viewer to the far
clipping plane (always positive).
<STRONG>DESCRIPTION</STRONG>
<STRONG>gluPerspective</STRONG> specifies a viewing frustum into the world
coordinate system. In general, the aspect ratio in
<STRONG>gluPerspective</STRONG> should match the aspect ratio of the
associated viewport. For example, aspect=2.0 means the
viewer's angle of view is twice as wide in <EM>x</EM> as it is in <EM>y</EM>.
If the viewport is twice as wide as it is tall, it displays
the image without distortion.
The matrix generated by <STRONG>gluPerspective</STRONG> is multipled by the
current matrix, just as if <STRONG>glMultMatrix</STRONG> were called with the
generated matrix. To load the perspective matrix onto the
current matrix stack instead, precede the call to
<STRONG>gluPerspective</STRONG> with a call to <STRONG>glLoadIdentity</STRONG>.
Given <EM>f</EM> defined as follows:
f = cotangent(<STRONG>____</STRONG>)
2
The generated matrix is
( )
| ___<STRONG>_</STRONG>__ |
| aspect 0 0 0 |
| |
| 0 f 0 0 |
| <STRONG>__________</STRONG> <STRONG>____________</STRONG> |
| 0 0 zNear-zFar zNear-zFar |
( )
0 0 -1 0
<STRONG>NOTES</STRONG>
Depth buffer precision is affected by the values specified
for <EM>zNear</EM> and <EM>zFar</EM>. The greater the ratio of <EM>zFar</EM> to <EM>zNear</EM>
is, the less effective the depth buffer will be at
distinguishing between surfaces that are near each other.
If
r = _<STRONG>____</STRONG>
zNear
roughly log r bits of depth buffer precision are lost.
Because r a<STRONG>p</STRONG>proaches infinity as <EM>zNear</EM> approaches 0, <EM>zNear</EM>
must never be set to 0.
<STRONG>SEE</STRONG> <STRONG>ALSO</STRONG>
<STRONG>glFrustum</STRONG>, <STRONG>glLoadIdentity</STRONG>, <STRONG>glMultMatrix</STRONG>, <STRONG>gluOrtho2D</STRONG>
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