GLORTHO() MachTen Programmer’s Manual GLORTHO()

NAME
glOrtho - multiply the current matrix with an orthographic
matrix

C SPECIFICATION
void glOrtho( GLdouble left,
GLdouble right,
GLdouble bottom,
GLdouble top,
GLdouble zNear,
GLdouble zFar )

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.

zNear, zFar Specify the distances to the nearer and far-
ther depth clipping planes. These values are
negative if the plane is to be behind the
viewer.

DESCRIPTION
glOrtho describes a transformation that produces a paral-
lel projection. The current matrix (see glMatrixMode) is
multiplied by this matrix and the result replaces the cur-
rent matrix, as if glMultMatrix were called with the fol-
lowing matrix as its argument:

left ( matrix {
ccol { {2 over {"right" - "left"}} above 0 above 0
above 0 }
ccol { 0 above {2 over {"top" - "bottom"}} above 0
above 0 }
ccol { 0 above 0 above {-2 over {"zFar" - "zNear"}}
above 0 }
ccol { {t sub x}~ above {t sub y}~ above {t sub z}~
above 1~ } } right )

where
t sub x ~=~ -{{"right" + "left"} over {"right" - "left"}}

t sub y ~=~ -{{"top" + "bottom"} over {"top" - "bottom"}}

t sub z ~=~ -{{"zFar" + "zNear"} over {"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.

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

MachTen 2