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GLLIGHT(3G) GLLIGHT(3G)
NAME
glLightf, glLighti, glLightfv, glLightiv - set light source parameters
C SPECIFICATION
void glLightf( GLenum light,
GLenum pname,
GLfloat param )
void glLighti( GLenum light,
GLenum pname,
GLint param )
PARAMETERS
light 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.
pname Specifies a single-valued light source parameter for light. GL_SPOT_EXPONENT,
GL_SPOT_CUTOFF, GL_CONSTANT_ATTENUATION, GL_LINEAR_ATTENUATION, and GL_QUADRATIC_ATTENUATION
are accepted.
param Specifies the value that parameter pname of light source light will be set to.
C SPECIFICATION
void glLightfv( GLenum light,
GLenum pname,
const GLfloat *params )
void glLightiv( GLenum light,
GLenum pname,
const GLint *params )
PARAMETERS
light 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.
pname Specifies a light source parameter for light. 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.
params Specifies a pointer to the value or values that parameter pname of light source light will be
set to.
DESCRIPTION
glLight sets the values of individual light source parameters. light names the light and is a sym-
bolic name of the form GL_LIGHTi, where 0 <= i < GL_MAX_LIGHTS. pname specifies one of ten light
source parameters, again by symbolic name. params 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 initially disabled. When it is enabled, light sources that are enabled contribute to the
lighting calculation. Light source i is enabled and disabled using glEnable and glDisable with argu-
ment GL_LIGHTi.
The ten light parameters are as follows:
GL_AMBIENT params contains four integer or floating-point values that specify the ambient
RGBA intensity of the light. Integer values are mapped linearly such that the
most positive representable value maps to 1.0, and the most negative repre-sentable representable
sentable value maps to -1.0. Floating-point values are mapped directly. Neither
integer nor floating-point values are clamped. The initial ambient light inten-sity intensity
sity is (0, 0, 0, 1).
GL_DIFFUSE params 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 representable value maps to 1.0, and the most negative repre-sentable representable
sentable 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 initial value is (0, 0, 0, 0).
GL_SPECULAR params 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 representable value maps to 1.0, and the most negative repre-sentable representable
sentable 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 initial value is (0, 0, 0, 0).
GL_POSITION params 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 floating-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 directional source. Diffuse and
specular lighting calculations take the light's direction, but not its actual
position, into account, and attenuation is disabled. Otherwise, diffuse and
specular lighting calculations are based on the actual location of the light in
eye coordinates, and attenuation is enabled. The initial position is (0, 0, 1,
0); thus, the initial light source is directional, parallel to, and in the direc-tion direction
tion of the -z axis.
GL_SPOT_DIRECTION params contains three integer or floating-point values that specify the direction
of the light in homogeneous object coordinates. Both integer and floating-point
values are mapped directly. Neither integer nor floating-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 coordi-nates. coordinates.
nates. It is significant only when GL_SPOT_CUTOFF is not 180, which it is ini-tially. initially.
tially. The initial direction is (0, 0, -1).
GL_SPOT_EXPONENT params is a single integer or floating-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 attenuated 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 params is a single integer or floating-point value that specifies the maximum
spread angle of a light source. Integer and floating-point values are mapped
directly. Only values in the range [0,90] and the special 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 distribution.
GL_CONSTANT_ATTENUATION
GL_LINEAR_ATTENUATION
GL_QUADRATIC_ATTENUATION
params is a single integer or floating-point value that specifies one of the
three light attenuation factors. Integer and floating-point values are mapped
directly. Only nonnegative values are accepted. If the light is positional,
rather than directional, its intensity is attenuated by the reciprocal of the sum
of the constant factor, the linear factor times the distance between the light
and the vertex being lighted, and the quadratic factor times the square of the
same distance. The initial attenuation factors are (1, 0, 0), resulting in no
attenuation.
NOTES
It is always the case that GL_LIGHTi = GL_LIGHT0 + i.
ERRORS
GL_INVALID_ENUM is generated if either light or pname 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 nega-tive negative
tive attenuation factor is specified.
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(3G), glLightModel(3G), glMaterial(3G)
GLLIGHT(3G)
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