- specify material parameters for the lighting model
C SPECIFICATION
PARAMETERS
_param1 Specifies which face or faces are being updated.
Must be one of GL_FRONT, GL_BACK, or
GL_FRONT_AND_BACK.
_param2 Specifies the single-valued material parameter of
the face or faces that is being updated. Must be
GL_SHININESS.
_param3 Specifies the value that parameter GL_SHININESS
will be set to.
C SPECIFICATION
PARAMETERS
_param1
Specifies which face or faces are being updated.
Must be one of GL_FRONT, GL_BACK, or
GL_FRONT_AND_BACK.
_param2
Specifies the material parameter of the face or
faces that is being updated. Must be one of
GL_AMBIENT, GL_DIFFUSE, GL_SPECULAR, GL_EMISSION,
GL_SHININESS, GL_AMBIENT_AND_DIFFUSE, or
GL_COLOR_INDEXES.
_param3
Specifies a pointer to the value or values that
_param2 will be set to.
DESCRIPTION
glMaterial assigns values to material parameters. There
are two matched sets of material parameters. One, the
front-facing set, is used to shade points, lines, bitmaps,
and all polygons (when two-sided lighting is disabled), or
just front-facing polygons (when two-sided lighting is
enabled). The other set, back-facing, is used to shade
back-facing polygons only when two-sided lighting is
enabled. Refer to the glLightModel reference page for
details concerning one- and two-sided lighting calcula-
tions.
glMaterial takes three arguments. The first, _param1,
specifies whether the GL_FRONT materials, the GL_BACK
materials, or both GL_FRONT_AND_BACK materials will be
modified. The second, _param2, specifies which of several
parameters in one or both sets will be modified. The
third, _param3, specifies what value or values will be
most negative representable value maps
to -1.0. Floating-point values are
mapped directly. Neither integer nor
floating-point values are clamped.
The initial ambient reflectance for
both front- and back-facing materials
is (0.2, 0.2, 0.2, 1.0).
GL_DIFFUSE _param3 contains four integer or
floating-point values that specify the
diffuse RGBA reflectance of the mate-
rial. Integer values are mapped lin-
early such that the most positive rep-
resentable value maps to 1.0, and the
most negative representable value maps
to -1.0. Floating-point values are
mapped directly. Neither integer nor
floating-point values are clamped.
The initial diffuse reflectance for
both front- and back-facing materials
is (0.8, 0.8, 0.8, 1.0).
GL_SPECULAR _param3 contains four integer or
floating-point values that specify the
specular RGBA reflectance of the mate-
rial. Integer values are mapped lin-
early such that the most positive rep-
resentable value maps to 1.0, and the
most negative representable value maps
to -1.0. Floating-point values are
mapped directly. Neither integer nor
floating-point values are clamped.
The initial specular reflectance for
both front- and back-facing materials
is (0, 0, 0, 1).
GL_EMISSION _param3 contains four integer or
floating-point values that specify the
RGBA emitted light intensity of the
material. Integer values are mapped
linearly such that the most positive
representable value maps to 1.0, and
the most negative representable value
maps to -1.0. Floating-point values
are mapped directly. Neither integer
nor floating-point values are clamped.
The initial emission intensity for
both front- and back-facing materials
is (0, 0, 0, 1).
GL_SHININESS _param3 is a single integer or float-
ing-point value that specifies the
floating-point values specifying the
color indices for ambient, diffuse,
and specular lighting. These three
values, and GL_SHININESS, are the only
material values used by the color
index mode lighting equation. Refer
to the glLightModel reference page for
a discussion of color index lighting.
NOTES
The material parameters can be updated at any time. In
particular, glMaterial can be called between a call to
glBegin and the corresponding call to glEnd. If only a
single material parameter is to be changed per vertex,
however, glColorMaterial is preferred over glMaterial (see
glColorMaterial).
While the ambient, diffuse, specular and emission material
parameters all have alpha components, only the diffuse
alpha component is used in the lighting computation.
ERRORS
GL_INVALID_ENUM is generated if either _param1 or _param2
is not an accepted value.
GL_INVALID_VALUE is generated if a specular exponent out-
side the range [0,128] is specified.
ASSOCIATED GETS
glGetMaterial
SEE ALSO
glColorMaterial, glLight, glLightModel
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