1991-2006 Silicon Graphics, Inc.

glGetLight

3G

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/.