2 KiB
_glFrontFace: define front- and back-facing polygons
Syntax
SUB _glFrontFace (BYVAL mode AS _UNSIGNED LONG) void _glFrontFace(GLenum mode);
; mode
Specifies the orientation of front-facing polygons. _GL_CW and _GL_CCW are accepted. The initial 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. 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 front-facing. By default, counterclockwise polygons are taken to be front-facing.
Error(s)
_GL_INVALID_ENUM is generated if mode is not an accepted value.
Use With
_glGet with argument _GL_FRONT_FACE
See Also
Copyright 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see [http://oss.sgi.com/projects/FreeB/ http://oss.sgi.com/projects/FreeB/].