glFrontFace — define front- and back-facing polygons
void fsfuncglFrontFace( | GLenum mode); |
mode
Specifies the orientation of front-facing polygons.
GL_CW and
GL_CCW are accepted. The initial value is
GL_CCW.
In a scene composed entirely of opaque closed surfaces,
back-facing polygons are never visible. Eliminating (culling) these
invisible polygons has the obvious benefit of speeding up the
rendering of the image. To enable and disable culling, call
glEnable and
glDisable
with argument GL_CULL_FACE.
Culling is initially disabled.
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.
Copyright © 2003-2004 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.