glShadeModel(3)

NAME

       glShadeModel - select flat or smooth shading

C SPECIFICATION

       void glShadeModel( GLenum mode )

       delim $$

PARAMETERS

       mode  Specifies  a  symbolic  value  representing  a shading technique.
             Accepted values are GL_FLAT and GL_SMOOTH.  The initial value  is
             GL_SMOOTH.

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 glBegin 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.

                     --------------------------------------------
                     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 glShadeModel with mode set  to
       GL_FLAT and GL_SMOOTH, respectively.

ERRORS

       GL_INVALID_ENUM is generated if mode is any value other than GL_FLAT or
       GL_SMOOTH.

       GL_INVALID_OPERATION is generated if glShadeModel is  executed  between
       the execution of glBegin and the corresponding execution of glEnd.

ASSOCIATED GETS

       glGet with argument GL_SHADE_MODEL

SEE ALSO

       glBegin(3G), glColor(3G), glLight(3G), glLightModel(3G)

                                                              GLSHADEMODEL(3G)