GLGETLIGHT() MachTen Programmer’s Manual GLGETLIGHT()

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 )

delim $$

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 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_LIGHT$i$ for
0<=$i$<GL_MAX_LIGHTS, where GL_MAX_LIGHTS is an implemen-
tation dependent constant that is greater than or equal to
eight. pname specifies one of ten light source parame-
ters, again by symbolic name.

The following parameters are defined:

GL_AMBIENT params 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 params returns four integer or float-
ing-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 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
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 float-
ing-point values representing the
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 params 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 params returns three integer or float-
ing-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 params returns a single integer or
floating-point value representing the
spot exponent of the light. An inte-
ger 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 com-
puted by rounding the internal float-
ing-point representation to the near-
est integer. The initial value is 180.

GL_CONSTANT_ATTENUATION
params returns a single integer or
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
params 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
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 con-
tents 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 exe-
cuted between the execution of glBegin and the correspond-
ing execution of glEnd.