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ortho(3G)							     ortho(3G)


NAME    [Toc]    [Back]

     ortho, ortho2 - define an orthographic projection transformation

C SPECIFICATION    [Toc]    [Back]

     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    [Toc]    [Back]

     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    [Toc]    [Back]

     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 eyecoordinates
 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 windowcoordinates
 by the	commands:





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ortho(3G)							     ortho(3G)



	  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    [Toc]    [Back]

      
      
     mmode, perspective, viewport, window


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