fglFrontFace(3G) OpenGL Reference fglFrontFace(3G)NAME
fglFrontFace - define front- and back-facing polygons
FORTRAN SPECIFICATION
SUBROUTINE fglFrontFace( INTEGER*4 mode )
PARAMETERS
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 fglEnable and
fglDisable 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.
fglFrontFace 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 fglFrontFace is executed between the
execution of fglBegin and the corresponding execution of fglEnd.
ASSOCIATED GETS
fglGet with argument GL_FRONT_FACE
SEE ALSO
fglCullFace, fglLightModel
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