glFrontFace(3G)		       OpenGL Reference		       glFrontFace(3G)

NAME    [Toc]    [Back]

     glFrontFace - define front- and back-facing polygons

C SPECIFICATION    [Toc]    [Back]

     void glFrontFace( GLenum mode )

PARAMETERS    [Toc]    [Back]

     mode  Specifies the orientation of	front-facing polygons.	GL_CW and
	   GL_CCW are accepted.	 The initial value is GL_CCW.

DESCRIPTION    [Toc]    [Back]

     In	a scene	composed entirely of opaque closed surfaces, back-facing
     polygons are never	visible.  Eliminating these invisible polygons has the
     obvious benefit of	speeding up the	rendering of the image.	 To enable and
     disable elimination of back-facing	polygons, call glEnable	and glDisable
     with argument GL_CULL_FACE.

     The projection of a polygon to window coordinates is said to have
     clockwise winding if an imaginary object following	the path from its
     first vertex, its second vertex, and so on, to its	last vertex, and
     finally back to its first vertex, moves in	a clockwise direction about
     the interior of the polygon.  The polygon's winding is said to be
     counterclockwise if the imaginary object following	the same path moves in
     a counterclockwise	direction about	the interior of	the polygon.
     glFrontFace specifies whether polygons with clockwise winding in window
     coordinates, or counterclockwise winding in window	coordinates, are taken
     to	be front-facing.  Passing GL_CCW to mode selects counterclockwise
     polygons as front-facing; GL_CW selects clockwise polygons	as frontfacing.
  By default, counterclockwise polygons are	taken to be frontfacing.

ERRORS    [Toc]    [Back]

     GL_INVALID_ENUM is	generated if mode is not an accepted value.

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

ASSOCIATED GETS    [Toc]    [Back]

     glGet with	argument GL_FRONT_FACE

SEE ALSO    [Toc]    [Back]

     glCullFace, glLightModel


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