NAME
glFrontFace
- define front- and back-facing polygons
C SPECIFICATION
void
glFrontFace(
GLenum
mode )
delim $$
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
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.
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(3G),
glLightModel(3G)
Index
- NAME
-
- C SPECIFICATION
-
- PARAMETERS
-
- DESCRIPTION
-
- ERRORS
-
- ASSOCIATED GETS
-
- SEE ALSO
-
