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glShadeModel

Chapter 17

400

glShadeModel

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.

Flat and smooth shading are speciﬁed by glShadeModel with mode set to GL_FLAT and

GL_SMOOTH, respectively.

Primitive Type of Polygon i Vertex

Single polygon (i≡ 1) 1

Triangle strip i + 2

Triangle fan i + 2

Independent triangle 3i

Quad strip 2i + 2

Independent quad 4i

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