NAME¶
glLight - 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 depends on the
implementation, but at least eight lights are supported. They are identified
by symbolic names of the form GL_LIGHTi, where i ranges from 0 to the
value of GL_MAX_LIGHTS - 1.
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_LIGHTi, where i ranges from 0 to the
value of GL_MAX_LIGHTS - 1.
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 i ranges from 0 to the value of GL_MAX_LIGHTS
- 1. 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, 1).
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, 1).
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 upper 3x3 of the
modelview matrix when glLight is called, 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(), glLightModel(),
glMaterial()