- return light source parameter values
C SPECIFICATION
PARAMETERS
_param1 Specifies a light source. The number of possible
lights depends on the implementation, 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.
_param2 Specifies a light source parameter for _param1.
Accepted symbolic names are 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.
_param3 Returns the requested data.
DESCRIPTION
glGetLight returns in _param3 the value or values of a
light source parameter. _param1 names the light and is a
symbolic name of the form GL_LIGHTi for 0 <= i <
GL_MAX_LIGHTS, where GL_MAX_LIGHTS is an implementation
dependent constant that is greater than or equal to eight.
_param2 specifies one of ten light source parameters,
again by symbolic name.
The following parameters are defined:
GL_AMBIENT _param3 returns four integer or float-
ing-point values representing the
ambient intensity of the light source.
Integer values, when requested, are
linearly mapped from the internal
floating-point representation such
that 1.0 maps to the most positive
representable integer value, and -1.0
maps to the most negative repre-
sentable integer value. If the inter-
nal value is outside the range [-1,
1], the corresponding integer return
value is undefined. The initial value
is (0, 0, 0, 1).
GL_DIFFUSE _param3 returns four integer or float-
ing-point values representing the dif-
fuse intensity of the light source.
Integer values, when requested, are
linearly mapped from the internal
specular intensity of the light
source. Integer values, when
requested, are linearly mapped from
the internal floating-point represen-
tation such that 1.0 maps to the most
positive representable integer value,
and -1.0 maps to the most negative
representable integer value. If the
internal value is outside the range
[-1, 1], the corresponding integer
return value is undefined. The initial
value for GL_LIGHT0 is (1, 1, 1, 1);
for other lights, the initial value is
(0, 0, 0, 0).
GL_POSITION _param3 returns four integer or float-
ing-point values representing the
position of the light source. Integer
values, when requested, are computed
by rounding the internal floating-
point values to the nearest integer
value. The returned values are those
maintained in eye coordinates. They
will not be equal to the values speci-
fied using glLight, unless the mod-
elview matrix was identity at the time
glLight was called. The initial value
is (0, 0, 1, 0).
GL_SPOT_DIRECTION _param3 returns three integer or
floating-point values representing the
direction of the light source. Inte-
ger values, when requested, are com-
puted by rounding the internal float-
ing-point values to the nearest inte-
ger value. The returned values are
those maintained in eye coordinates.
They will not be equal to the values
specified using glLight, unless the
modelview matrix was identity at the
time glLight was called. Although
spot direction is normalized before
being used in the lighting equation,
the returned values are the trans-
formed versions of the specified val-
ues prior to normalization. The ini-
tial value is (0, 0, -1).
GL_SPOT_EXPONENT _param3 returns a single integer or
floating-point value representing the
spot exponent of the light. An inte-
ger value, when requested, is computed
floating-point value representing the
constant (not distance-related) atten-
uation of the light. An integer
value, when requested, is computed by
rounding the internal floating-point
representation to the nearest integer.
The initial value is 1.
GL_LINEAR_ATTENUATION
_param3 returns a single integer or
floating-point value representing the
linear attenuation of the light. An
integer value, when requested, is com-
puted by rounding the internal float-
ing-point representation to the near-
est integer. The initial value is 0.
GL_QUADRATIC_ATTENUATION
_param3 returns a single integer or
floating-point value representing the
quadratic attenuation of the light.
An integer value, when requested, is
computed by rounding the internal
floating-point representation to the
nearest integer. The initial value is
0.
NOTES
It is always the case that GL_LIGHTi = GL_LIGHT0 + i.
If an error is generated, no change is made to the con-
tents of _param3.
ERRORS
GL_INVALID_ENUM is generated if _param1 or _param2 is not
an accepted value.
GL_INVALID_OPERATION is generated if glGetLight is exe-
cuted between the execution of glBegin and the correspond-
ing execution of glEnd.
SEE ALSO
glLight
1