gluPerspective - set up a perspective projection matrix
void gluPerspective( GLdouble fovy, GLdouble aspect, GLdouble zNear, GLdouble zFar )
fovy Specifies the field of view angle, in degrees, in the y direction. aspect Specifies the aspect ratio that determines the field of view in the x direction. The aspect ratio is the ratio of x (width) to y (height). zNear Specifies the distance from the viewer to the near clipping plane (always positive). zFar Specifies the distance from the viewer to the far clipping plane (always positive).
gluPerspective specifies a viewing frustum into the world coordinate
system. In general, the aspect ratio in gluPerspective 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 x as it is in y. If the viewport
is twice as wide as it is tall, it displays the image without distortion.
The matrix generated by gluPerspective is multipled by the current matrix,
just as if glMultMatrix were called with the generated matrix. To load the
perspective matrix onto the current matrix stack instead, precede the call
to gluPerspective with a call to glLoadIdentity.
Given f defined as follows:
fovy
f = cotangent(----)
2
The generated matrix is
| f |
| ------ 0 0 0 |
| aspect |
| |
| 0 f 0 0 |
| |
| zFar+zNear 2*zFar*zNear |
| 0 0 ---------- ------------ |
| zNear-zFar zNear-zFar |
| |
| 0 0 -1 0 |
Depth buffer precision is affected by the values specified for zNear and
zFar. The greater the ratio of zFar to zNear is, the less effective the
depth buffer will be at distinguishing between surfaces that are near each
other. If
zFar
r = -----
zNear
roughly log r bits of depth buffer precision are lost. Because r
2
approaches infinity as zNear approaches zero, zNear must never be set to
zero.
glFrustum, glLoadIdentity, glMultMatrix, gluOrtho2D
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Last Edited: Mon, May 22, 1995