
GLLIGHT(3G) OpenGL Manual GLLIGHT(3G)
NAME
glLight  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 i ranges from 0 to the value of GL_MAX_LIGHTS  1.
pname
Specifies a singlevalued 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 i ranges from 0 to the value of GL_MAX_LIGHTS  1.
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 i ranges from 0 to the value of
GL_MAX_LIGHTS  1. 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 argument GL_LIGHTi.
The ten light parameters are as follows:
GL_AMBIENT
params contains four integer or floatingpoint 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. Floatingpoint values are mapped directly. Neither integer nor floatingpoint
values are clamped. The initial ambient light intensity is (0, 0, 0, 1).
GL_DIFFUSE
params contains four integer or floatingpoint 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. Floatingpoint values are mapped directly. Neither integer nor floatingpoint
values are clamped. The initial value for GL_LIGHT0 is (1, 1, 1, 1); for other lights,
the initial value is (0, 0, 0, 1).
GL_SPECULAR
params contains four integer or floatingpoint 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. Floatingpoint values are mapped directly. Neither integer nor floatingpoint
values are clamped. The initial value for GL_LIGHT0 is (1, 1, 1, 1); for other lights,
the initial value is (0, 0, 0, 1).
GL_POSITION
params contains four integer or floatingpoint values that specify the position of the
light in homogeneous object coordinates. Both integer and floatingpoint values are
mapped directly. Neither integer nor floatingpoint 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 direction of the  z axis.
GL_SPOT_DIRECTION
params contains three integer or floatingpoint values that specify the direction of
the light in homogeneous object coordinates. Both integer and floatingpoint values
are mapped directly. Neither integer nor floatingpoint values are clamped.
The spot direction is transformed by the upper 3x3 of the modelview matrix when
glLight is called, 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 floatingpoint value that specifies the intensity
distribution of the light. Integer and floatingpoint 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 floatingpoint value that specifies the maximum spread
angle of a light source. Integer and floatingpoint 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 floatingpoint value that specifies one of the three
light attenuation factors. Integer and floatingpoint 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 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()
COPYRIGHT
Copyright (C) 19912006 Silicon Graphics, Inc. This document is licensed under the SGI
Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.
AUTHORS
opengl.org
opengl.org 06/10/2014 GLLIGHT(3G) 
