GLLIGHT(3G) UNIX Programmer's Manual 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 sup-
ported. 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
MirBSD #10-current Printed 2021-12-07 1
GLLIGHT(3G) UNIX Programmer's Manual GLLIGHT(3G)
Specifies a pointer to the value or values that parame-
ter pname of light source light will be set to.
DESCRIPTION
glLight sets the values of individual light source parame-
ters. 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 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 ini-
tially 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
MirBSD #10-current Printed 2021-12-07 2
GLLIGHT(3G) UNIX Programmer's Manual GLLIGHT(3G)
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. 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 com-
ponent of the position is 0, the light
is treated as a directional source. Dif-
fuse and specular lighting calculations
take the light's direction, but not its
actual position, into account, and
attenuation is disabled. Otherwise, dif-
fuse and specular lighting calculations
are based on the actual location of the
light in eye coordinates, and attenua-
tion is enabled. The initial 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. 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. 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-
MirBSD #10-current Printed 2021-12-07 3
GLLIGHT(3G) UNIX Programmer's Manual GLLIGHT(3G)
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
MirBSD #10-current Printed 2021-12-07 4
GLLIGHT(3G) UNIX Programmer's Manual GLLIGHT(3G)
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 negative attenuation factor is speci-
fied.
GL_INVALID_OPERATION is generated if glLight is executed
between the execution of glBegin and the corresponding exe-
cution of glEnd.
ASSOCIATED GETS
glGetLight
glIsEnabled with argument GL_LIGHTING
SEE ALSO
glColorMaterial(3G), glLightModel(3G), glMaterial(3G)
MirBSD #10-current Printed 2021-12-07 5