## 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*