glLight, glLightf, glLighti, glLightfv, glLightiv  set
light source parameters
void glLightf(
GLenum light,
GLenum pname,
GLfloat param ); void glLighti(
GLenum light,
GLenum pname,
GLint param );
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. 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. 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 );
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. 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. 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_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: params contains
four integer or floatingpoint 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. Floatingpoint values are mapped
directly. Neither integer nor floatingpoint values are
clamped. The initial ambient light intensity is (0, 0, 0,
1). params contains four integer or floatingpoint 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. Floatingpoint values
are mapped directly. Neither integer 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). params contains four integer or floatingpoint
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. Floatingpoint
values are mapped directly. Neither integer 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). params contains four integer or
floatingpoint values that specify the position of the
light in homogeneous object coordinates. Both integer and
floatingpoint values are mapped directly. Neither integer
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. params contains three integer or
floatingpoint values that specify the direction of
the light in homogeneous object coordinates. Both
integer and floatingpoint values are mapped
directly. Neither integer nor floatingpoint 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). params is a
single integer or floatingpoint value that specifies
the intensity distribution of the light. Integer
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. params is a single integer
or floatingpoint value that specifies the maximum
spread angle of a light source. Integer 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
params is a single integer or floatingpoint value that
specifies one of the three light attenuation factors.
Integer 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.
It is always the case that GL_LIGHTi = 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(3), glLightModel(3), glMaterial(3)
glLight(3G)
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