NAME
	  glViewport - set the viewport


     C SPECIFICATION
	  void glViewport( GLint x,
			   GLint y,
			   GLsizei width,
			   GLsizei height )


     PARAMETERS
	  x, y Specify the lower left corner of	the viewport
	       rectangle, in pixels. The initial value is (0,0).

	  width, height
	       Specify the width and height of the viewport.  When a
	       GL context is first attached to a window, width and
	       height are set to the dimensions	of that	window.

     DESCRIPTION
	  glViewport specifies the affine transformation of x and y
	  from normalized device coordinates to	window coordinates.
	  Let (x  , y  ) be normalized device coordinates.  Then the
	  windowncoordinates (x	, y ) are computed as follows:
			       w   w
			    x  = (x  +1)(_____)	+ x
			     w	   nd	(  2  )
			    y  = (y  +1)(______) + y
			     w	   nd	(  2   )
	  Viewport width and height are	silently clamped to a range
	  that depends on the implementation.  To query	this range,
	  call glGet with argument GL_MAX_VIEWPORT_DIMS.

     ERRORS
	  GL_INVALID_VALUE is generated	if either width	or height is
	  negative.

	  GL_INVALID_OPERATION is generated if glViewport is executed
	  between the execution	of glBegin and the corresponding
	  execution of glEnd.

     ASSOCIATED	GETS
	  glGet	with argument GL_VIEWPORT
	  glGet	with argument GL_MAX_VIEWPORT_DIMS

     SEE ALSO
	  glDepthRange