**eqn not supported**

*mode*- Specifies a symbolic value representing
a shading technique. Accepted values are
**GL_FLAT**and**GL_SMOOTH**. The initial value is**GL_SMOOTH**.

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.

**GL_INVALID_OPERATION**
is generated if **glShadeModel** is executed between the execution of **glBegin**
and the corresponding execution of **glEnd**.