GLLIGHT
Section: Misc. Reference Manual Pages (3G)
Page Index
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 )
delim $$
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 0 ≤ $ i $ < GL_MAX_LIGHTS.
- 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 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_LIGHT$i$,
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_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, 0).
- 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, 0).
- 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 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 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(3G),
glLightModel(3G),
glMaterial(3G)