glShadeModel man page on RedHat
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GLSHADEMODEL(3G) OpenGL Manual 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.
┌───────────────────────────────────┬───────────────────────────────────┐
│ │ │
│ Primitive │ Vertex │
│Type of Polygon │ │
│ i │ │
│ │ │
├───────────────────────────────────┼───────────────────────────────────┤
│Single polygon │ 1 │
│ ( │ │
│ │ │
│ │ │
│ i │ │
│ == │ │
│ 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(), glColor(), glLight(), glLightModel()
COPYRIGHT
Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed
under the SGI Free Software B License. For details, see
http://oss.sgi.com/projects/FreeB/.
AUTHORS
opengl.org
opengl.org 03/16/2013 GLSHADEMODEL(3G)
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