NAME¶
glGetLight - 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_LIGHT i where i ranges
from 0 to the value of GL_MAX_LIGHTS - 1.
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_LIGHT i where i ranges from 0 to the value of
GL_MAX_LIGHTS - 1. 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_LIGHT i = 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().