glFrontFace
[New
- Windows 95, OEM Service Release 2]
The glFrontFace
function defines front- and back-facing polygons.
void glFrontFace(
|
GLenum mode |
|
|
); |
|
Parameters
mode
The
orientation of front-facing polygons. GL_CW and GL_CCW are accepted. The
default value is GL_CCW.
Remarks
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. You enable and disable elimination of
back-facing polygons with glEnable and glDisable194O61P using 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. The glFrontFace function 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.
The following
function retrieves information about glFrontface:
glGet with
argument GL_FRONT_FACE
Error Codes
The following
are the error codes generated and their conditions.
|
Error
Code |
Condition |
|
GL_INVALID_ENUM
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mode was not an accepted value. |
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GL_INVALID_OPERATION
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glFrontFace was called between a call to glBegin and the
corresponding call to glEnd. |
See Also