## 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 $i$ 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 executed between the execution of glBegin and the corresponding execution of glEnd.

## Associated Gets

glGet with argument GL_SHADE_MODEL