GLenum pname,
GLfloat param )
void GLAPIENTRY glLighti( GLenum light,
GLenum pname,
GLint param )
PARAMETERS
light Specifies a light. The number of lights depends on the implemen‐
tation, but at least eight lights are supported. They are iden‐
tified 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 GLAPIENTRY glLightfv( GLenum light,
GLenum pnam )
void GLAPIENTRY glLightiv( GLenum light,
GLenum pnam )
PARAMETERS
light Specifies a light. The number of lights depends on the implemen‐
tation, but at least eight lights are supported. They are iden‐
tified by symbolic names of the form GL_LIGHTi where 0 ≤ i <
GL_MAX_LIGHTS.
pnam 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 pnam 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. pnam specifies one of ten light source parameters,
again by symbolic name.
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 cal‐
culation. Light source i is enabled and disabled using glEnable and
glDisable with argument GL_LIGHTi.
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
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
contains four integer or floating-point values that
specify the position of the light in homogeneous ob‐
ject 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 com‐
ponent 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 en‐
abled. 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
contains three integer or floating-point values
that specify the direction of the light in homoge‐
neous object coordinates. Both integer and float‐
ing-point values are mapped directly. Neither inte‐
ger 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 coor‐
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 dis‐
tribution.
GL_SPOT_CUTOFF
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 an‐
gle between the direction of the light and the di‐
rection from the light to the vertex being lighted
is greater than the spot cutoff angle, the light is
completely masked. Otherwise, its intensity is con‐
trolled 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
is a single integer or floating-point value that
specifies one of the three light attenuation fac‐
tors. 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 fac‐
tors 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 pnam is not an accepted
value.
GL_INVALID_VALUE is generated if a spot exponent value is specified out‐
side 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 ex‐
ecution of glBegin and the corresponding execution of glEnd.
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