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glFrontFace - define front- and back-facing polygons
void
glFrontFace( GLenum mode )
eqn not supported
- 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 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.
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.
glGet with argument GL_FRONT_FACE
glCullFace(3G)
,
glLightModel(3G)
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