glOrtho example c c++ java objc

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

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, seehttp://oss.sgi.com/projects/FreeB/.

Example

void reshape (int w, int h)
{
   // Set viewport area.
   glViewport (0, 0, (GLsizei) w, (GLsizei) h);
   glMatrixMode (GL_PROJECTION);
   glLoadIdentity ();

   if (w <= h)
      glOrtho(-50.0, 50.0, -50.0*(GLfloat)h/(GLfloat)w, 50.0*(GLfloat)h/(GLfloat)w, -1.0, 1.0);
   else
      glOrtho (-50.0*(GLfloat)w/(GLfloat)h,50.0*(GLfloat)w/(GLfloat)h, -50.0, 50.0, -1.0, 1.0);

   glMatrixMode(GL_MODELVIEW);
}