glGetLight.3gl

Name

  glGetLightfv,	glGetLightiv - 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_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 parameters are as	follows:

  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.

  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.

  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.

  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.

  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.

  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.

  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.

  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.

  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.

  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.

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.

  GL_INVALID_OPERATION is generated if glGetLight is called between a call to
  glBegin and the corresponding	call to	glEnd.

See Also

  glLight

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Last Edited: Fri, May 26, 1995

AFV