GLUPERSPECTIVE() MachTen Programmer’s Manual GLUPERSPECTIVE()

NAME
gluPerspective - set up a perspective projection matrix

C SPECIFICATION
void gluPerspective( GLdouble fovy,
GLdouble aspect,
GLdouble zNear,
GLdouble zFar )

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PARAMETERS
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).

DESCRIPTION
gluPerspective specifies a viewing frustum into the world
coordinate system. In general, the aspect ratio in glu-
Perspective should match the aspect ratio of the associ-
ated 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 glu-
Perspective with a call to glLoadIdentity.

Given f defined as follows:

f ~=~ cotangent"("{"fovy" over 2}")"

The generated matrix is

left ( ~~ down 130 { matrix {
ccol { {f over "aspect"} above 0 above 0 above 0 }
ccol { 0 above f above 0 above 0 }
ccol { 0 above 0 above {{"zFar" + "zNear"} over
{"zNear" - "zFar"}} above -1 }
ccol { 0 above 0 above {{2 * "zFar" * "zNear"} over
{"zNear" - "zFar"}} above 0} }} ~~~ right )

NOTES
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

$r ~=~ "zFar" over "zNear"$

roughly $log sub 2 r$ bits of depth buffer precision are
lost. Because $r$ approaches infinity as zNear approaches
0, zNear must never be set to 0.

SEE ALSO
glFrustum, glLoadIdentity, glMultMatrix, gluOrtho2D

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