NAME
fglLightf, fglLighti, fglLightfv, fglLightiv - set light
source parameters
FORTRAN SPECIFICATION
SUBROUTINE fglLightf( INTEGER*4 light,
INTEGER*4 pname,
REAL*4 param )
SUBROUTINE fglLighti( INTEGER*4 light,
INTEGER*4 pname,
INTEGER*4 param )
PARAMETERS
light Specifies a light. The number of 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 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.
FORTRAN SPECIFICATION
SUBROUTINE fglLightfv( INTEGER*4 light,
INTEGER*4 pname,
CHARACTER*8 params )
SUBROUTINE fglLightiv( INTEGER*4 light,
INTEGER*4 pname,
CHARACTER*8 params )
PARAMETERS
light
Specifies a light. The number of 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.
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.
params
Specifies a pointer to the value or values that
parameter pname of light source light will be set to.
DESCRIPTION
fglLight 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. pname
specifies one of ten light source parameters, again by
symbolic name. params is either a single value or a pointer
to an array that contains the new values.
To enable and disable lighting calculation, call fglEnable
and fglDisable with argument GL_LIGHTING. Lighting is
initially disabled. When it is enabled, light sources that
are enabled contribute to the lighting calculation. Light
source i is enabled and disabled using fglEnable and
fglDisable with argument GL_LIGHTi.
The ten light parameters are as follows:
GL_AMBIENT params contains four integer or
floating-point values that specify the
ambient 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 ambient light intensity is (0,
0, 0, 1).
GL_DIFFUSE params 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 params 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 params contains four integer or
floating-point values that specify the
position of the light in homogeneous
object 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 fglLight is called
(just as if it were a point), and it is
stored in eye coordinates. If the w
component 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 enabled.
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 params contains three integer or
floating-point values that specify the
direction of the light in homogeneous
object coordinates. Both integer and
floating-point values are mapped
directly. Neither integer nor
floating-point values are clamped.
The spot direction is transformed by the
inverse of the modelview matrix when
fglLight is called (just as if it were a
normal), and it is stored in eye
coordinates. It is significant only
when GL_SPOT_CUTOFF is not 180, which it
is initially. The initial direction is
(0, 0, -1).
GL_SPOT_EXPONENT params is a single integer or floating-
point value that specifies the intensity
distribution of the light. Integer and
floating-point values are mapped
directly. Only values in the range
[0,128] are accepted.
Effective light intensity is attenuated
by the cosine of the angle between the
direction of the light and the direction
from the light to the vertex being
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 distribution.
GL_SPOT_CUTOFF params 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 angle between the
direction of the light and the direction
from the light to the vertex being
lighted is greater than the spot cutoff
angle, the light is completely masked.
Otherwise, its intensity is controlled
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
params is a single integer or floating-
point value that specifies one of the
three light attenuation factors.
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
factors 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 pname is not
an accepted value.
GL_INVALID_VALUE is generated if a spot exponent value is
specified outside 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 fglLight is executed
between the execution of fglBegin and the corresponding
execution of fglEnd.
ASSOCIATED GETS
fglGetLight
fglIsEnabled with argument GL_LIGHTING
SEE ALSO
fglColorMaterial, fglLightModel, fglMaterial