glLight — set light source parameters
void glLightf( | GLenum | light, |
GLenum | pname, | |
GLfloat | param) ; |
void glLighti( | GLenum | light, |
GLenum | pname, | |
GLint | param) ; |
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
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.
void glLightfv( | GLenum | light, |
GLenum | pname, | |
const GLfloat * | params) ; |
void glLightiv( | GLenum | light, |
GLenum | pname, | |
const GLint * | params) ; |
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
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.
glLight
sets the values of individual light source parameters.
light
names the light and is a symbolic name of the form GL_LIGHT
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
GL_LIGHT
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
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
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
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
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
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
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
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.
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
GL_INVALID_OPERATION
is generated if glLight
is executed between
the execution of
glBegin and the corresponding execution of glEnd.
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/.