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Alphabetical
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glLight(3G)
NAME
glLight, glLightf, glLighti, glLightfv, glLightiv - set light source
parameters
SYNOPSIS
void glLightf(
GLenum light,
GLenum pname,
GLfloat param );
void glLighti(
GLenum light,
GLenum pname,
GLint 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 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.
SYNOPSIS
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_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 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_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.
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(3), glLightModel(3), glMaterial(3)
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Index for
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Alphabetical
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