gluPerspective(3G)	       OpenGL Reference		    gluPerspective(3G)

NAME    [Toc]    [Back]

     gluPerspective - set up a perspective projection matrix

C SPECIFICATION    [Toc]    [Back]

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

PARAMETERS    [Toc]    [Back]

     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    [Toc]    [Back]

     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:

				f = cotangent(____)
					       2













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gluPerspective(3G)	       OpenGL Reference		    gluPerspective(3G)



     The generated matrix is

		    (					     )
		    |  ______				     |
		    |  aspect  0      0		   0	     |
		    |					     |
		    |	 0     f      0		   0	     |
		    |		  __________  ____________   |
		    |	 0     0  zNear-zFar   zNear-zFar    |
		    (					     )
			 0     0      -1	   0

NOTES    [Toc]    [Back]

     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 = _____
					 zNear

     roughly log 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    [Toc]    [Back]

     glFrustum,	glLoadIdentity,	glMultMatrix, gluOrtho2D


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