glOrtho.3gl




Name

  glOrtho - multiply the current matrix	by an orthographic matrix


C Specification

  void glOrtho(	GLdouble left,
		GLdouble right,
		GLdouble bottom,
		GLdouble top,
		GLdouble near,
		GLdouble far )


Parameters


  left,	right Specify the coordinates for the left and right vertical
	      clipping planes.

  bottom, top Specify the coordinates for the bottom and top horizontal
	      clipping planes.

  near,	far   Specify the distances to the nearer and farther depth clipping
	      planes.  These distances are negative if the plane is to be
	      behind the viewer.


Description

  glOrtho describes a perspective matrix that produces a parallel projection.
  (left, bottom,  -near) and (right, top,  -near) specify the points on	the
  near clipping	plane that are mapped to the lower left	and upper right
  corners of the window, respectively, assuming	that the eye is	located	at
  (0, 0, 0).  -far specifies the location of the far clipping plane.  Both
  near and far can be either positive or negative.  The	corresponding matrix
  is

		    |     2	     		          |
		    |----------      0          0      t  |
		    |right-left				x |
		    |					  |
		    |		      2    		  |
		    |    0       ----------	0      t  |
		    |	  	 top-bottom	        y |
		    |                                     |
		    |					  |
		    |	 0	     0	        -2        |
		    |                        --------  t  |
		    |			     far-near	z |
		    |                                     |
		    |	 0	     0		0      1  |

  where
			              right+left
			       t  = - ----------
				x     right-left

				      top+bottom
			       t  = - ----------
				y     top-bottom

				       far+near
				t  = - --------
				 z     far-near

  The current matrix is	multiplied by this matrix with the result replacing
  the current matrix.  That is,	if M is	the current matrix and O is the	ortho
  matrix, then M is replaced with M  O.

  Use glPushMatrix and glPopMatrix to save and restore the current matrix
  stack.

Errors

  GL_INVALID_OPERATION is generated if glOrtho is executed between the
  execution of	glBegin	and the	corresponding execution	of glEnd.

Associated Gets

  glGet	with argument GL_MATRIX_MODE
  glGet	with argument GL_MODELVIEW_MATRIX
  glGet	with argument GL_PROJECTION_MATRIX
  glGet	with argument GL_TEXTURE_MATRIX

See Also

  glFrustum, glMatrixMode, glMultMatrix, glPushMatrix, glViewport



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Last Edited: Mon, May 22, 1995

AFV