GLSHADEMODEL() MachTen Programmer’s Manual GLSHADEMODEL()

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 raster-
ized, typically assigning different colors to each result-
ing 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 seg-
ment $i$ 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 box; 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 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 exe-
cuted between the execution of glBegin and the correspond-
ing execution of glEnd.

ASSOCIATED GETS
glGet with argument GL_SHADE_MODEL

SEE ALSO
glBegin, glColor, glLight, glLightModel

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