glGetLightfv, glGetLightxv
- return light source parameter values
void glGetLightfv(GLenum light, GLenum pname, GLfloat * params)
void glGetLightxv(GLenum light, GLenum pname, GLfixed * params)
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_EMISSION
, GL_SPOT_DIRECTION
, GL_SPOT_EXPONENT
, GL_SPOT_CUTOFF
, GL_CONSTANT_ATTENUATION
, GL_LINEAR_ATTENUATION
, and GL_QUADRATIC_ATTENUATION
.
params
Returns the requested data.
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 ten light parameters are defined:
GL_AMBIENT
params
returns 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
returns 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
returns 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
returns four fixed-point or floating-point values representing the emitted light intensity of the material. Both fixed-point and floating-point values are mapped directly. The initial value is (0, 0, 0, 1).
GL_SPOT_DIRECTION
params
returns 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 initial direction is (0, 0, -1).
GL_SPOT_EXPONENT
params
returns 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. The initial spot exponent is 0.
GL_SPOT_CUTOFF
params
returns 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.
GL_CONSTANT_ATTENUATION
, GL_LINEAR_ATTENUATION
, GL_QUADRATIC_ATTENUATION
params
returns 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).
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
.
GL_INVALID_ENUM
is generated if light
or pname
is not an accepted value.
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/.