GLUPERSPECTIVE(3G)														GLUPERSPECTIVE(3G)

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:

								 f  = cotangent(fovy/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 effec-
       tive the depth buffer will be at distinguishing between surfaces that are near each other.  If

								     r = zFar/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.

SEE ALSO

       glFrustum, glLoadIdentity, glMultMatrix, gluOrtho2D

																GLUPERSPECTIVE(3G)