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# docs.GL

OpenGL 3
OpenGL 2

# glOrtho

## Name

glOrtho — multiply the current matrix with an orthographic matrix

## C Specification

`void glOrtho(` | GLdouble | left,
| GLdouble | right,
| GLdouble | bottom,
| GLdouble | top,
| GLdouble | nearVal,
| GLdouble | farVal`)`;

## 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.

`nearVal`, `farVal`

  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 t x 0 2 top - bottom 0 t y 0 0 -2 farVal - nearVal t z 0 0 0 1

where

t x = - right + left right - left

t y = - top + bottom top - bottom

t z = - farVal + nearVal farVal - nearVal

Typically, the matrix mode is `GL_PROJECTION`, and left bottom - nearVal and right top - nearVal 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). - farVal specifies the location of the far clipping plane. Both `nearVal` and `farVal` 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`.

`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_COLOR_MATRIX`

glGet with argument `GL_MODELVIEW_MATRIX`

glGet with argument `GL_PROJECTION_MATRIX`

glGet with argument `GL_TEXTURE_MATRIX`

## Tutorials

## See Also

glFrustum, glMatrixMode, glMultMatrix, glPushMatrix, glViewport

## Copyright

Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see https://web.archive.org/web/20171022161616/http://oss.sgi.com/projects/FreeB/.

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