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OpenGL 1.1 for AIX: Reference Manual

glShadeModel Subroutine


Selects flat or smooth shading.


OpenGL C bindings library: libGL.a

C Syntax

void glShadeModel(GLenum Mode)


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


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. Counting vertices and primitives from 1 (one) starting when the glBegin subroutine is issued, each flat-shaded line segment i is given the computed color of vertex + 1, its second vertex. Counting similarly from 1, each flat-shaded polygon is given the computed color of the vertex in the following list. 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 the Mode parameter set to GL_FLAT and GL_SMOOTH, respectively.


GL_INVALID_ENUM Mode is any value other than GL_FLAT or GL_SMOOTH.
GL_INVALID_OPERATION The glShadeModel subroutine is called between a call to glBegin and the corresponding call to glEnd.

Associated Gets

Associated gets for the glShadeModel subroutine are as follows. (See the glGet subroutine for more information.)

glGet with argument GL_SHADE_MODEL.


/usr/include/GL/gl.h Contains C language constants, variable type definitions, and ANSI function prototypes for OpenGL.

Related Information

The glBegin or glEnd subroutine, glColor subroutine, glLight subroutine, glLightModel subroutine.

OpenGL Overview.

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