glLightf man page on RedHat
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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_LIGHT i, where i ranges
from 0 to the value of GL_MAX_LIGHTS - 1.
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_LIGHT i, 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_LIGHT i, 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_LIGHT i.
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,
1).
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,
1).
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 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 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 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 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
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 attenuation factors
are (1, 0, 0), resulting in no attenuation.
NOTES
It is always the case that GL_LIGHT i = 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 © 1991-2006 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 03/16/2013 GLLIGHT(3G)
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