NAME
glGetLightfv, glGetLightiv - return light source parameter
values
C SPECIFICATION
void glGetLightfv( GLenum light,
GLenum pname,
GLfloat *params )
void glGetLightiv( GLenum light,
GLenum pname,
GLint *params )
PARAMETERS
light Specifies a light source. The number of possible
lights 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.
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.
params Returns the requested data.
DESCRIPTION
glGetLight returns in params the value or values of a light
source parameter. light 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. pname specifies one of
ten light source parameters, again by symbolic name.
The following parameters are defined:
GL_AMBIENT params returns four integer or
floating-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 representable
integer value. If the internal value is
outside the range [-1, 1], the
corresponding integer return value is
undefined. The initial value is (0, 0,
0, 1).
GL_DIFFUSE params returns four integer or
floating-point values representing the
diffuse 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 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_SPECULAR params returns four integer or
floating-point values representing the
specular 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 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 params returns four integer or
floating-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 specified using
glLight, unless the modelview matrix was
identity at the time glLight was called.
The initial value is (0, 0, 1, 0).
GL_SPOT_DIRECTION params returns three integer or
floating-point values representing the
direction 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 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
transformed versions of the specified
values prior to normalization. The
initial value is (0, 0, -1).
GL_SPOT_EXPONENT params returns a single integer or
floating-point value representing the
spot exponent 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.
GL_SPOT_CUTOFF params returns a single integer or
floating-point value representing the
spot cutoff angle 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
180.
GL_CONSTANT_ATTENUATION
params returns a single integer or
floating-point value representing the
constant (not distance-related)
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 1.
GL_LINEAR_ATTENUATION
params returns a single integer or
floating-point value representing the
linear 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.
GL_QUADRATIC_ATTENUATION
params 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 contents
of params.
ERRORS
GL_INVALID_ENUM is generated if light or pname is not an
accepted value.
GL_INVALID_OPERATION is generated if glGetLight is executed
between the execution of glBegin and the corresponding
execution of glEnd.
SEE ALSO
glLight