NAME

glShadeModel - select flat or smooth shading

C SPECIFICATION

void ggllSShhaaddeeMMooddeell( GLenum _m_o_d_e )

        

delim $$

PARAMETERS

_m_o_d_e
Specifies a symbolic value representing a shading technique. Accepted values are GGLL__FFLLAATT and GGLL__SSMMOOOOTTHH. The initial value is GGLL__SSMMOOOOTTHH.

DESCRIPTION

GL primitives can have either flat or smooth shading. Smooth shading, the default, causes the computed colors of vertices to be interpolated as the primitive is rasterized, typically assigning different colors to each resulting pixel fragment. Flat shading selects the computed color of just one vertex and assigns it to all the pixel fragments generated by rasterizing a single primitive. In either case, the computed color of a vertex is the result of lighting if lighting is enabled, or it is the current color at the time the vertex was specified if lighting is disabled.

Flat and smooth shading are indistinguishable for points. Starting when ggllBBeeggiinn is issued and counting vertices and primitives from 1, the GL gives each flat-shaded line segment $i$ the computed color of vertex $i ~+~ 1$, its second vertex. Counting similarly from 1, the GL gives each flat-shaded polygon the computed color of the vertex listed in the following table. This is the last vertex to specify the polygon in all cases except single polygons, where the first vertex specifies the flat-shaded color.

center;
lb cb
l c .
_
Primitive Type of Polygon $i$   Vertex
_
Single polygon ($ i ~==~ 1 $)   1
Triangle strip  $i ~+~ 2$
Triangle fan    $i ~+~ 2$
Independent triangle    $ 3 i$
Quad strip      $2 i ~+~ 2$
Independent quad        $ 4 i $
_


Flat and smooth shading are specified by ggllSShhaaddeeMMooddeell with _m_o_d_e set to GGLL__FFLLAATT and GGLL__SSMMOOOOTTHH, respectively.

ERRORS

GGLL__IINNVVAALLIIDD__EENNUUMM is generated if _m_o_d_e is any value other than GGLL__FFLLAATT or GGLL__SSMMOOOOTTHH.

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

ASSOCIATED GETS

ggllGGeett with argument GGLL__SSHHAADDEE__MMOODDEELL

SEE ALSO

ggllBBeeggiinn((33GG)), ggllCCoolloorr((33GG)), ggllLLiigghhtt((33GG)), ggllLLiigghhttMMooddeell((33GG))