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 depends on the
implementation, but at least eight lights are supported. They
are identified by symbolic names of the form GLLIGHTi where 0 <
i < the value returned by glGetIntegerv with parameter
GLMAXLIGHTS.
pname Specifies a single-valued light source parameter for light.
GLSPOTEXPONENT, GLSPOTCUTOFF, GLCONSTANTATTENUATION,
GLLINEARATTENUATION, and GLQUADRATICATTENUATION 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 GLLIGHTi where 0 < i < the
value returned by glGetIntegerv with parameter GLMAXLIGHTS.
pname
Specifies a light source parameter for light. GLAMBIENT,
GLDIFFUSE, GLSPECULAR, GLPOSITION, GLSPOTCUTOFF,
GLSPOTDIRECTION, GLSPOTEXPONENT, GLCONSTANTATTENUATION,
GLLINEARATTENUATION, and GLQUADRATICATTENUATION 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 GLLIGHTi, where 0 < i
< the value returned by glGetIntegerv with parameter GLMAXLIGHTS.
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 GLLIGHTING. 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 GLLIGHTi.
The ten light parameters are as follows:
GLAMBIENT 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).
GLDIFFUSE 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 GLLIGHT0 is (1, 1, 1, 1); for
other lights, the initial value is (0, 0, 0, 0).
GLSPECULAR 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 GLLIGHT0 is (1, 1,
1, 1); for other lights, the initial value is (0, 0,
0, 0).
GLPOSITION 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.
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glLight(3G) OpenGL Reference glLight(3G)
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 direction of the
-z axis.
GLSPOTDIRECTION 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
coordinates. It is significant only when
GLSPOTCUTOFF is not 180, which it is initially.
The initial direction is (0, 0, -1).
GLSPOTEXPONENT 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 GLSPOTCUTOFF, next paragraph). The initial
spot exponent is 0, resulting in uniform light
distribution.
GLSPOTCUTOFF 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.
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glLight(3G) OpenGL Reference glLight(3G)
Otherwise, its intensity is controlled by the spot
exponent and the attenuation factors. The initial
spot cutoff is 180, resulting in uniform light
distribution.
GLCONSTANTATTENUATION
GLLINEARATTENUATION
GLQUADRATICATTENUATION
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 GLLIGHTi = GLLIGHT0 + i.
ERRORS
GLINVALIDENUM is generated if either light or pname is not an accepted
value.
GLINVALIDVALUE 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.
GLINVALIDOPERATION is generated if glLight is executed between the
execution of glBegin and the corresponding execution of glEnd.
ASSOCIATED GETS
glGetLight
glIsEnabled with argument GLLIGHTING
SEE ALSO
glColorMaterial, glLightModel, glMaterial
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