glOrtho: multiply the current matrix with an orthographic matrix.
C Specification 
Parameters 
Description 
Errors 
Associated Gets 
See Also
void glOrtho(
GLdouble left,
GLdouble right,
GLdouble bottom,
GLdouble top,
GLdouble zNear,
GLdouble zFar)
 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.
 zNear, zFar
 Specify the distances to the nearer and farther depth clipping planes.
These values are negative if the plane is to be behind the viewer.
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:
A 
0 
0 
t_{x} 
0 
B 
0 
t_{y} 
0 
0 
C 
t_{z} 
0 
0 
0 
1 

where
 A =
 2 / (right
left)
 B =
 2 / (top
bottom)
 C =
 2 / (far
near)
 t_{x} =
 (right +
left) / (right
left)
 t_{y} =
 (top +
bottom) / (top
bottom)
 t_{z} =
 (zFar +
zNear) / (zFar
zNear)
Typically, the matrix mode is GL_PROJECTION, and
(left, bottom, zNear) and
(right, top, zNear) 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). zFar specifies the location of the far clipping plane.
Both zNear and zFar can be either positive or
negative.
Use glPushMatrix and glPopMatrix to save and restore the
current matrix stack.
 GL_INVALID_OPERATION is generated if glOrtho is executed between the execution
of glBegin and the corresponding
execution of glEnd.
glGet with argument
GL_MATRIX_MODE
glGet with argument
GL_MODELVIEW_MATRIX
glGet with argument
GL_PROJECTION_MATRIX
glGet with argument
GL_TEXTURE_MATRIX
glFrustum,
glMatrixMode,
glMultMatrix,
glPushMatrix,
glViewport