- set light source parameters
C SPECIFICATION
PARAMETERS
_param1 Specifies a light. The number of lights depends
on the implementation, but at least eight lights
are supported. They are identified by symbolic
names of the form GL_LIGHTi where 0 <= i <
GL_MAX_LIGHTS.
_param2 Specifies a single-valued light source parameter
for _param1. GL_SPOT_EXPONENT, GL_SPOT_CUTOFF,
GL_CONSTANT_ATTENUATION, GL_LINEAR_ATTENUATION,
and GL_QUADRATIC_ATTENUATION are accepted.
_param3 Specifies the value that parameter _param2 of
light source _param1 will be set to.
C SPECIFICATION
PARAMETERS
_param1
Specifies a light. The number of lights depends on
the implementation, but at least eight lights are
supported. They are identified by symbolic names
of the form GL_LIGHTi where 0 <= i < GL_MAX_LIGHTS.
_param2
Specifies a light source parameter for _param1.
GL_AMBIENT, GL_DIFFUSE, GL_SPECULAR, GL_POSITION,
GL_SPOT_CUTOFF, GL_SPOT_DIRECTION,
GL_SPOT_EXPONENT, GL_CONSTANT_ATTENUATION,
GL_LINEAR_ATTENUATION, and GL_QUADRATIC_ATTENUATION
are accepted.
_param3
Specifies a pointer to the value or values that
parameter _param2 of light source _param1 will be
set to.
DESCRIPTION
glLight sets the values of individual light source parame-
ters. _param1 names the light and is a symbolic name of
the form GL_LIGHTi, where 0 <= i < GL_MAX_LIGHTS. _param2
specifies one of ten light source parameters, again by
symbolic name. _param3 is either a single value or a
pointer to an array that contains the new values.
To enable and disable lighting calculation, call glEnable
and glDisable with argument GL_LIGHTING. Lighting is ini-
tially disabled. When it is enabled, light sources that
are enabled contribute to the lighting calculation. Light
floating-point values are clamped.
The initial ambient light intensity is
(0, 0, 0, 1).
GL_DIFFUSE _param3 contains four integer or
floating-point values that specify the
diffuse RGBA intensity of the light.
Integer values are mapped linearly
such that the most positive repre-
sentable 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 value for GL_LIGHT0 is (1,
1, 1, 1); for other lights, the ini-
tial value is (0, 0, 0, 0).
GL_SPECULAR _param3 contains four integer or
floating-point values that specify the
specular RGBA intensity of the light.
Integer values are mapped linearly
such that the most positive repre-
sentable 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 value for GL_LIGHT0 is (1,
1, 1, 1); for other lights, the ini-
tial value is (0, 0, 0, 0).
GL_POSITION _param3 contains four integer or
floating-point values that specify the
position of the light in homogeneous
object coordinates. Both integer and
floating-point values are mapped
directly. Neither integer nor float-
ing-point values are clamped.
The position is transformed by the
modelview matrix when glLight is
called (just as if it were a point),
and it is stored in eye coordinates.
If the w component of the position is
0, the light is treated as a direc-
tional source. Diffuse and specular
lighting calculations take the light's
direction, but not its actual posi-
tion, into account, and attenuation is
disabled. Otherwise, diffuse and
specular lighting calculations are
ing-point values are clamped.
The spot direction is transformed by
the inverse of the modelview matrix
when glLight is called (just as if it
were a normal), and it is stored in
eye coordinates. It is significant
only when GL_SPOT_CUTOFF is not 180,
which it is initially. The initial
direction is (0, 0, -1).
GL_SPOT_EXPONENT _param3 is a single integer or float-
ing-point value that specifies the
intensity distribution of the light.
Integer and floating-point values are
mapped directly. Only values in the
range [0,128] are accepted.
Effective light intensity is attenu-
ated by the cosine of the angle
between the direction of the light and
the direction from the light to the
vertex being lighted, raised to the
power of the spot exponent. Thus,
higher spot exponents result in a more
focused light source, regardless of
the spot cutoff angle (see
GL_SPOT_CUTOFF, next paragraph). The
initial spot exponent is 0, resulting
in uniform light distribution.
GL_SPOT_CUTOFF _param3 is a single integer or float-
ing-point value that specifies the
maximum spread angle of a light
source. Integer and floating-point
values are mapped directly. Only val-
ues in the range [0,90] and the spe-
cial value 180 are accepted. If the
angle between the direction of the
light and the direction from the light
to the vertex being lighted is greater
than the spot cutoff angle, the light
is completely masked. Otherwise, its
intensity is controlled by the spot
exponent and the attenuation factors.
The initial spot cutoff is 180,
resulting in uniform light distribu-
tion.
GL_CONSTANT_ATTENUATION
GL_LINEAR_ATTENUATION
quadratic factor times the square of
the same distance. The initial atten-
uation factors are (1, 0, 0), result-
ing in no attenuation.
NOTES
It is always the case that GL_LIGHTi = GL_LIGHT0 + i.
ERRORS
GL_INVALID_ENUM is generated if either _param1 or _param2
is not an accepted value.
GL_INVALID_VALUE is generated if a spot exponent value is
specified outside the range [0,128], or if spot cutoff is
specified outside the range [0,90] (except for the special
value 180), or if a negative attenuation factor is speci-
fied.
GL_INVALID_OPERATION is generated if glLight is executed
between the execution of glBegin and the corresponding
execution of glEnd.
ASSOCIATED GETS
glGetLight
glIsEnabled with argument GL_LIGHTING
SEE ALSO
glColorMaterial, glLightModel, glMaterial
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