Name

glOrtho — multiply the current matrix with an orthographic matrix

C Specification

void glOrthof(GLfloat left,
 GLfloat right,
 GLfloat bottom,
 GLfloat top,
 GLfloat near,
 GLfloat far);
 
void glOrthox(GLfixed left,
 GLfixed right,
 GLfixed bottom,
 GLfixed top,
 GLfixed near,
 GLfixed 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 values are negative if the plane is to be behind the viewer.

Description

glOrtho describes a transformation that produces a parallel projection. The current matrix (see glMatrixMode) is multiplied by this matrix and the result replaces the current matrix, as if glMultMatrix were called with the following matrix as its argument:

( 2 right-left 0 0 tx 0 2 top-bottom 0 ty 0 0 -2 far-near tz 0 0 0 1 )

where

tx = - right+left right-left ty = - top+bottom top-bottom tz = - far+near far-near

Typically, the matrix mode is GL_PROJECTION, and (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.

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

Errors

GL_INVALID_VALUE is generated if left = right, or bottom = top, or near = far.

See Also

glFrustum, glMatrixMode, glMultMatrix, glPushMatrix, glViewport

Copyright

Copyright © 2003-2004 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.