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*OpenGL 1.1 for AIX: Reference Manual*

## glOrtho Subroutine

### Purpose

Multiplies the current matrix by an orthographic matrix.

### Library

OpenGL C bindings library: **libGL.a**

### C Syntax

**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

The **glOrtho** subroutine 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 as follows:

where the following
statements apply:

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, M is replaced with MO.

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

### Errors

**GL_INVALID_OPERATION** |
The **glOrtho** subroutine is called between a call to **glBegin** and the corresponding call to **glEnd**. |

### Associated Gets

Associated gets for the **glOrtho** subroutine are as follows. (See the **glGet** subroutine for more information.)

**glGet** with argument **GL_MATRIX_MODE**

**glGet** with argument **GL_MODELVIEW_MATRIX**

**glGet** with argument **GL_PROJECTION_MATRIX**

**glGet** with argument **GL_TEXTURE_MATRIX**.

### Files

**/usr/include/GL/gl.h** |
Contains C language constants, variable type definitions, and ANSI function prototypes for OpenGL. |

### Related Information

The **glBegin** or **glEnd** subroutine, **glFrustum** subroutine, **glMatrixMode** subroutine, **glMultMatrix** subroutine, **glPushMatrix** subroutine, **glViewport** subroutine.

OpenGL Overview.

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