gluPerspective.3gl

Name

  gluPerspective - set up a perspective	projection matrix

C Specification

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

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 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         |

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
                                       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.

See Also

  glFrustum, glLoadIdentity, glMultMatrix, gluOrtho2D

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Last Edited: Fri Dec 6 11:18:03 EST 1996 by AFV
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