glShadeModel(3G) OpenGL Reference glShadeModel(3G)NAME
glShadeModel - select flat or smooth shading
C SPECIFICATION
void glShadeModel( GLenum mode )
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.
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Primitive Type of Polygon i Vertex
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Single polygon (i = 1) 1
Triangle strip i + 2
Triangle fan i + 2
Independent triangle 3i
Quad strip 2i + 2
Independent quad 4i
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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.
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glShadeModel(3G) OpenGL Reference glShadeModel(3G)
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, glColor, glLight, glLightModel
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