glLightf
, glLightx
, glLightfv
, glLightxv
- set light source parameters
void glLightf(GLenum light, GLenum pname, GLfloat param) void glLightx(GLenum light, GLenum pname, GLfixed param)
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_LIGHT
i 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.
void glLightfv(GLenum light, GLenum pname, const GLfloat * params) void glLightxv(GLenum light, GLenum pname, const GLfixed * params)
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_LIGHT
i where 0 ≤ i < GL_MAX_LIGHTS
.
pname
Specifies a light source parameter for light
. GL_AMBIENT
, GL_DIFFUSE
, GL_SPECULAR
, GL_EMISSION
, 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.
glLight
sets the values of individual light source parameters. light
names the light and is a symbolic name of the form GL_LIGHT
i, 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 glEnable
and glDisable
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 glEnable
and glDisable
with argument GL_LIGHT
i.
The ten light parameters are as follows:
GL_AMBIENT
params
contains four fixed-point or floating-point values that specify the ambient RGBA intensity of the light. Both fixed-point and floating-point values are mapped directly. Neither fixed-point nor floating-point values are clamped. The initial ambient light intensity is (0, 0, 0, 1).
GL_DIFFUSE
params
contains four fixed-point or floating-point values that specify the diffuse RGBA intensity of the light. Both fixed-point and floating-point values are mapped directly. Neither fixed-point 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 fixed-point or floating-point values that specify the specular RGBA intensity of the light. Both fixed-point and floating-point values are mapped directly. Neither fixed-point 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_EMISSION
params
contains four fixed-point or floating-point values that specify the RGBA emitted light intensity of the material. Both fixed-point and floating-point values are mapped directly. Neither fixed-point nor floating-point values are clamped. The initial emission intensity for both front and back facing materials is (0, 0, 0, 1).
GL_SPOT_DIRECTION
params
contains three fixed-point or floating-point values that specify the direction of the light in homogeneous object coordinates. Both fixed-point and floating-point values are mapped directly. Neither fixed-point nor floating-point values are clamped.
The spot direction is transformed by the inverse of the modelview matrix when glLight
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 fixed-point or floating-point value that specifies the intensity distribution of the light. Fixed-point 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 fixed-point or floating-point value that specifies the maximum spread angle of a light source. Fixed-point 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 fixed-point or floating-point value that specifies one of the three light attenuation factors. Fixed-point 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.
It is always the case that GL_LIGHT
i = GL_LIGHT0
+ i.
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.
Copyright © 2003-2004 Silicon Graphics, Inc.
This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.