NAME

glFrontFace - define front- and back-facing polygons

C SPECIFICATION

void ggllFFrroonnttFFaaccee( GLenum _m_o_d_e )

        

delim $$

PARAMETERS

_m_o_d_e
Specifies the orientation of front-facing polygons. GGLL__CCWW and GGLL__CCCCWW are accepted. The initial value is GGLL__CCCCWW.

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 ggllEEnnaabbllee and ggllDDiissaabbllee with argument GGLL__CCUULLLL__FFAACCEE.

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. ggllFFrroonnttFFaaccee specifies whether polygons with clockwise winding in window coordinates, or counterclockwise winding in window coordinates, are taken to be front-facing. Passing GGLL__CCCCWW to _m_o_d_e selects counterclockwise polygons as front-facing; GGLL__CCWW selects clockwise polygons as front-facing. By default, counterclockwise polygons are taken to be front-facing.

ERRORS

GGLL__IINNVVAALLIIDD__EENNUUMM is generated if _m_o_d_e is not an accepted value.

GGLL__IINNVVAALLIIDD__OOPPEERRAATTIIOONN is generated if ggllFFrroonnttFFaaccee is executed between the execution of ggllBBeeggiinn and the corresponding execution of ggllEEnndd.

ASSOCIATED GETS

ggllGGeett with argument GGLL__FFRROONNTT__FFAACCEE

SEE ALSO

ggllCCuullllFFaaccee((33GG)), ggllLLiigghhttMMooddeell((33GG))