20032004
Silicon Graphics, Inc.
glLight
3G
glLight
glLightf
glLightx
glLightfv
glLightxv
set light source parameters
C Specification
void glLightf
GLenum light
GLenum pname
GLfloat param
void glLightx
GLenum light
GLenum pname
GLfixed 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 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 glLightxv
GLenum light
GLenum pname
const GLfixed * 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_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
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 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 fixedpoint or floatingpoint values that
specify the ambient RGBA intensity of the light. Both
fixedpoint and floatingpoint values are mapped
directly. Neither fixedpoint nor floatingpoint values
are clamped. The initial ambient light intensity is (0,
0, 0, 1).
GL_DIFFUSE
params
contains four fixedpoint or floatingpoint values that
specify the diffuse RGBA intensity of the light. Both
fixedpoint and floatingpoint values are mapped
directly. Neither fixedpoint 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, 0).
GL_SPECULAR
params
contains four fixedpoint or floatingpoint values that
specify the specular RGBA intensity of the light. Both
fixedpoint and floatingpoint values are mapped
directly. Neither fixedpoint 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, 0).
GL_POSITION
params contains four fixedpoint or floatingpoint values that specify
the position of the light in homogeneous object coordinates.
Both fixedpoint and floatingpoint values are mapped directly.
Neither fixedpoint 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 fixedpoint or floatingpoint values that
specify the direction of the light in homogeneous object
coordinates. Both fixedpoint and floatingpoint values
are mapped directly. Neither fixedpoint 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 fixedpoint or floatingpoint value that
specifies the intensity distribution of the light.
Fixedpoint 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 fixedpoint or floatingpoint value that
specifies the maximum spread angle of a light source.
Fixedpoint 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 fixedpoint or floatingpoint value that
specifies one of the three light attenuation factors.
Fixedpoint 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.
See Also
glEnable,
glLightModel,
glMaterial
Copyright
Copyright 20032004
Silicon Graphics, Inc. This document is licensed under the SGI
Free Software B License. For details, see
http://oss.sgi.com/projects/FreeB/.