glLight(3G)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
Specifies a light. The number of lights depends on the implementation,
but at least eight lights are supported. They are identified by sym‐
bolic names of the form GL_LIGHTi where 0 <= i < GL_MAX_LIGHTS. Speci‐
fies a single-valued light source parameter for light. GL_SPOT_EXPO‐
NENT, 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.
SYNOPSIS
void glLightfv(
GLenum light,
GLenum pname,
const GLfloat *params ); void glLightiv(
GLenum light,
GLenum pname,
const GLint *params );
PARAMETERS
Specifies a light. The number of lights depends on the implementation,
but at least eight lights are supported. They are identified by sym‐
bolic 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.
DESCRIPTIONglLight() 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 parame‐
ters, 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 glDis‐
able() with argument GL_LIGHTING. Lighting is initially disabled. When
it is enabled, light sources that are enabled contribute to the light‐
ing calculation. Light source i is enabled and disabled using glEn‐
able() and glDisable() with argument GL_LIGHTi.
The ten light parameters are as follows: 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). 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). 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). 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 dis‐
abled. 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 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 mod‐
elview 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
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. params is a single
integer or floating-point value that specifies the maximum
spread angle of a light source. Integer and floating-point val‐
ues are mapped directly. Only values in the range [0,90] and the
special value 180 are accepted. If the angle between the direc‐
tion 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 floating-point value that specifies one
of the three light attenuation factors. Integer and floating-point val‐
ues are mapped directly. Only nonnegative values are accepted. If the
light is positional, rather than directional, its intensity is attenu‐
ated 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 dis‐
tance. 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 GETSglGetLight()glIsEnabled() with argument GL_LIGHTING
SEE ALSOglColorMaterial(3), glLightModel(3), glMaterial(3)glLight(3G)