The glOrtho function multiplies the current matrix by an orthographic matrix.

void glOrtho(
  GLdouble left,
  GLdouble right,
  GLdouble bottom,
  GLdouble top,
  GLdouble zNear,
  GLdouble zFar


left, right
The coordinates for the left-and right-vertical clipping planes.
bottom, top
The coordinates for the bottom- and top-horizontal clipping planes.
zNear, zFar
The distances to the nearer and farther depth clipping planes. These distances are negative if the plane is to be behind the viewer.


The glOrtho function describes a perspective matrix that produces a parallel projection. The (left, bottom, near) and (right, top, near) parameters 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). The far parameter specifies the location of the far clipping plane. Both near and far can be either positive or negative. The corresponding matrix is


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. Use glMatrixMode to set the current matrix.

The following functions retrieve information related to glOrtho:

glGet with argument GL_MATRIX_MODE

glGet with argument GL_MODELVIEW_MATRIX

glGet with argument GL_PROJECTION_MATRIX

glGet with argument GL_TEXTURE_MATRIX

Error Codes

The following is the error code and its condition.

Error code Condition
GL_INVALID_OPERATION glOrtho was called between a call to glBegin and the corresponding call to glEnd.


  Windows NT/2000: Requires Windows NT 3.5 or later.
  Windows 95/98: Requires Windows 95 or later. Available as a redistributable for Windows 95.
  Header: Declared in Gl.h.
  Library: Use Opengl32.lib.

See Also

glBegin, glEnd, glFrustum, glMatrixMode, glMultMatrix, glPushMatrix, glViewport