ortho(3G)

NAME
     ortho, ortho2 - define an orthographic projection transformation

C SPECIFICATION
     void ortho(Coord left, Coord right, Coord bottom, Coord top,
                Coord near, Coord far)

     void ortho2(Coord left, Coord right, Coord bottom, Coord top)

     The above routines are functionally the same.  They differ only in that
     ortho is used for 3-D applications and ortho2 is used for 2-D
     applications.

PARAMETERS
     left     expects the coordinate for the left vertical clipping plane.

     right    expects the coordinate for the right vertical clipping plane.

     bottom   expects the coordinate for the bottom horizontal clipping plane.

     top      expects the coordinate for the top horizontal clipping plane.

     near     expects the distance to the nearer depth clipping plane.

     far      expects the distance to the farther depth clipping plane.

DESCRIPTION
     ortho specifies a box-shaped enclosure in the eye coordinate system that
     is mapped to the viewport. left, right, bottom, top, near, and far
     specify the location of the x, y, and z clipping planes. near and far are
     distances along the line of sight from the eye space origin; the z
     clipping planes are at -near and -far.

     ortho2 is the 2-D version of ortho.  It specifies a rectangle that is
     mapped to the viewport.  When you use ortho2 with 3-D world coordinates,
     the z coordinates are not transformed and will be clipped if they lie
     outside the range -1 < z  < 1.

     When the system is in single matrix mode, both ortho and ortho2 load a
     matrix onto the matrix stack, thus replacing the current top matrix.
     When the system is in viewing, projection, or texture matrix mode, the
     system replaces the current Projection matrix without changing the
     ModelView matrix stack or the Texture matrix.

     GL window coordinates have integer values at the centers of pixels.  Thus
     to correctly specify a one-to-one orthographic mapping from eye-
     coordinates to window-coordinates, the edges of the viewable volume
     should be set to 1/2-pixel values.  For example, the 1280 x 1024 full
     screen is correctly mapped one-to-one from eye-coordinates to window-
     coordinates by the commands:
          ortho2(-0.5,1279.5,-0.5,1023.5);
          viewport(0,1279,0,1023);


     Note that ortho, unlike perspective and window, allows the viewpoint to
     be moved from the origin of the coordinate system.  Thus ortho combines a
     trivial viewing transformation (translation from the origin) with its
     projection operation.  Be sure not to duplicate the orthographic
     translation in your viewing transformation.

SEE ALSO
     mmode, perspective, viewport, window