glShadeModel
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.
| Primitive Type of Polygon
| Vertex
|
| Single polygon (i = 1) | 1
|
| Triangle strip | i + 2
|
| Triangle fan | i + 2
|
| Independent triangle | 3i
|
| Quad strip | 2i + 2
|
| Independent quad | 4i
|
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,
glColor,
glLight,
glLightModel