Name

glGetLight — return light source parameter values

C Specification

void glGetLightfv(GLenum light,
 GLenum pname,
 GLfloat * params);
 
void glGetLightxv(GLenum light,
 GLenum pname,
 GLfixed * 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_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_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_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_POSITION

params returns four fixed-point or floating-point values representing the position of the light source. Both fixed-point and floating-point values are mapped directly. 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 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).

Notes

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.

Errors

GL_INVALID_ENUM is generated if light or pname is not an accepted value.

See Also

glLight

Copyright

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/.