glLight
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 imple-
mentation, 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 imple-
mentation, 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 symbolic name of the form GL_LIGHTi, where 0
≤ i < GL_MAX_LIGHTS. pname specifies one of ten light source parame-
ters, 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 argument 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 representable
value maps to -1.0. Floating-point values are
mapped directly. Neither integer nor floating-
point values are clamped. The initial ambient
light intensity 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 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
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 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
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. Nei-
ther 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 ini-
tial position is (0, 0, 1, 0); thus, the initial
light source is directional, parallel to, and in
the direction 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. Nei-
ther 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 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 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 ver-
tex 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 uni-
form 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 inten-
sity 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), 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 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 negative
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)
