glFrontFace.3gl

Name

  glFrontFace -	define front- and back-facing polygons

C Specification

  void glFrontFace( GLenum mode	)

Parameters

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

Description

  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.  Elimination of
  back-facing polygons is enabled and disabled with glEnable and glDisable
  using	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	front-facing.  By default, counterclockwise
  polygons are taken to	be front-facing.

Errors

  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

  glGet	with argument GL_FRONT_FACE

See Also

  glCullFace, glLightModel

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Last Edited: Fri Dec 6 11:18:03 EST 1996 by AFV
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