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glLightf, glLighti, glLightfv, glLightiv - set light source parameters
void glLightf( GLenum light,
GLenum pname,
GLfloat param )
void glLighti( GLenum light,
GLenum pname,
GLint param )
eqn not supported
- 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.
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$i$ 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.
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.
It is always the case that GL_LIGHT$i$ = GL_LIGHT0
+ $i$.
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.
glGetLight
glIsEnabled with argument GL_LIGHTING
glColorMaterial(3G)
, glLightModel(3G)
,
glMaterial(3G)
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