GLGETLIGHT(3G)

NAME
glGetLight - return light source parameter values

C SPECIFICATION

void glGetLightfv(GLenum light, GLenum pname, GLfloat * params);

void glGetLightiv(GLenum light, GLenum pname, GLint * 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_LIGHT i where i ranges from 0 to the value of GL_MAX_LIGHTS - 1.

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 where i ranges from 0 to the value of GL_MAX_LIGHTS - 1. 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 following parameters are defined:

GL_AMBIENT
    params returns four integer or floating-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 representable integer value. If the internal 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 floating-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 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_SPECULAR
    params returns four integer or floating-point values representing the specular 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 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 floating-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 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 integer or floating-point values representing the direction 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 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 transformed versions of the specified values prior to normalization. The initial 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 integer 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 computed by rounding the internal floating-point representation to the nearest integer. The initial value is 180.

GL_CONSTANT_ATTENUATION
    params returns a single integer or floating-point value representing the constant (not distance-related) 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 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 computed by rounding the internal floating-point representation to the nearest 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 contents 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 executed between the execution of glBegin() and the corresponding execution of glEnd().

SEE ALSO

glLight()

COPYRIGHT

Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.