glLight
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)
PARAMETERS
- light
-
Specifies a light. The number of lights is 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.
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 is 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_DIRECTION, GL_SPOT_EXPONENT,
GL_SPOT_CUTOFF, 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.
Lighting calculation is enabled and disabled using
glEnable and
glDisable with argument
GL_LIGHTING. When lighting 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 default ambient light
intensity is (0.0, 0.0, 0.0, 1.0).
- 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 default diffuse intensity is
(0.0, 0.0, 0.0, 1.0) for all lights other than light zero. The default
diffuse intensity of light zero is (1.0, 1.0, 1.0, 1.0).
- 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 default specular intensity is
(0.0, 0.0, 0.0, 1.0) for all lights other than light zero. The default
specular intensity of light zero is (1.0, 1.0, 1.0, 1.0).
- 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 0.0, 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 default position is (0,0,1,0); thus, the default 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 it 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 by default. The default
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 next paragraph). The default
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 default 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 default 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, 180], 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 called between
a call to glBegin and the corresponding
call to glEnd.
ASSOCIATED GETS
glGetLight
glIsEnabled with argument
GL_LIGHTING
SEE ALSO
glColorMaterial,
glLightModel,
glMaterial
back to the OpenGL index page
© 1995 Uwe Behrens. All rights reserved.