gllight - Man Page
glLight(3G) OpenGL Reference 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 is 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_DIRECTION,
GL_SPOT_EXPONENT, GL_SPOT_CUTOFF, 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.
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glLight(3G) OpenGL Reference glLight(3G)
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 parameters,
again by symbolic name. params is either a single value or a pointer to
an array that contains the new values.
Lighting calculation is enabled and disabled using glEnable and glDisable
with argument GL_LIGHTING. When lighting 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
default ambient light intensity is (0.0, 0.0, 0.0,
1.0).
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
default diffuse intensity is (0.0, 0.0, 0.0, 1.0) for
all lights other than light zero. The default
diffuse intensity of light zero is (1.0, 1.0, 1.0,
1.0).
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 default specular intensity is (0.0,
0.0, 0.0, 1.0) for all lights other than light zero.
The default specular intensity of light zero is (1.0,
1.0, 1.0, 1.0).
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
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glLight(3G) OpenGL Reference glLight(3G)
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 0.0, 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 default position is
(0,0,1,0); thus, the default 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
it 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 by default.
The default 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 next paragraph). The default 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
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glLight(3G) OpenGL Reference glLight(3G)
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
default 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
default 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 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, glLightModel, glMaterial
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