gluPerspective - set up a perspective projection matrix
void gluPerspective( | GLfloat | fovy, |
GLfloat | aspect, | |
GLfloat | zNear, | |
GLfloat | 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 glMultMatrixf
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 | | | | | | 0 0 zFar+zNear 2 x zFar x zNear | | ---------- ---------------- | | 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 log2(r) bits of depth buffer precision are lost.
Because r approaches infinity as zNear
approaches 0,
zNear
must never be set to 0.
Copyright c 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.