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GLLIGHT(3G)							   GLLIGHT(3G)

NAME
       glLightf, glLighti, glLightfv, glLightiv - set light source parameters

C SPECIFICATION
       void glLightf( GLenum light,
		      GLenum pname,
		      GLfloat param )
       void glLighti( GLenum light,
		      GLenum pname,
		      GLint param )

PARAMETERS
       light   Specifies  a light.  The number of lights depends on the imple‐
	       mentation, 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 single-valued light	source	parameter  for	light.
	       GL_SPOT_EXPONENT,    GL_SPOT_CUTOFF,   GL_CONSTANT_ATTENUATION,
	       GL_LINEAR_ATTENUATION,	and    GL_QUADRATIC_ATTENUATION	   are
	       accepted.

       param   Specifies  the value that parameter pname of light source light
	       will be set to.

C SPECIFICATION
       void glLightfv( GLenum light,
		       GLenum pname,
		       const GLfloat *params )
       void glLightiv( GLenum light,
		       GLenum pname,
		       const GLint *params )

PARAMETERS
       light  Specifies a light.  The number of lights depends on  the	imple‐
	      mentation,  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.  GL_AMBIENT,
	      GL_DIFFUSE,    GL_SPECULAR,     GL_POSITION,     GL_SPOT_CUTOFF,
	      GL_SPOT_DIRECTION,   GL_SPOT_EXPONENT,  GL_CONSTANT_ATTENUATION,
	      GL_LINEAR_ATTENUATION,	and    GL_QUADRATIC_ATTENUATION	   are
	      accepted.

       params Specifies	 a pointer to the value or values that parameter pname
	      of light source light will be set to.

DESCRIPTION
       glLight sets the values of individual light source  parameters.	 light
       names the light and is a symbolic name of the form GL_LIGHTi, where 0 ≤
       i < GL_MAX_LIGHTS.  pname specifies one of ten light source parameters,
       again  by  symbolic name.  params is either a single value or a pointer
       to an array that contains the new values.

       To enable and disable lighting calculation, call glEnable and glDisable
       with  argument GL_LIGHTING. Lighting is initially disabled.  When it is
       enabled, light sources that are enabled contribute to the lighting cal‐
       culation.   Light  source  i is enabled and disabled using glEnable and
       glDisable with argument GL_LIGHTi.

       The ten light parameters are as follows:

       GL_AMBIENT	   params contains four integer or floating-point val‐
			   ues	that specify the ambient RGBA intensity of the
			   light.  Integer values  are	mapped	linearly  such
			   that	 the most positive representable value maps to
			   1.0, and the most negative representable value maps
			   to	-1.0.	 Floating-point	  values   are	mapped
			   directly.  Neither integer nor floating-point  val‐
			   ues	are clamped.  The initial ambient light inten‐
			   sity is (0, 0, 0, 1).

       GL_DIFFUSE	   params contains four integer or floating-point val‐
			   ues	that specify the diffuse RGBA intensity of the
			   light.  Integer values  are	mapped	linearly  such
			   that	 the most positive representable value maps to
			   1.0, and the most negative representable value maps
			   to	-1.0.	 Floating-point	  values   are	mapped
			   directly.  Neither integer nor floating-point  val‐
			   ues	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 contains four integer or floating-point val‐
			   ues that specify the specular RGBA intensity of the
			   light.   Integer  values  are  mapped linearly such
			   that the most positive representable value maps  to
			   1.0, and the most negative representable value maps
			   to  -1.0.	Floating-point	 values	  are	mapped
			   directly.   Neither integer nor floating-point val‐
			   ues 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 contains four integer or floating-point val‐
			   ues that specify the position of the light in homo‐
			   geneous  object  coordinates.   Both	 integer   and
			   floating-point values are mapped directly.  Neither
			   integer nor floating-point values are clamped.

			   The position is transformed by the modelview matrix
			   when	 glLight  is  called  (just  as	 if  it were a
			   point), and it is stored in	eye  coordinates.   If
			   the	w component of the position is 0, the light is
			   treated as a directional source.  Diffuse and spec‐
			   ular	 lighting calculations take the light's direc‐
			   tion, but not its actual  position,	into  account,
			   and	attenuation  is	 disabled.  Otherwise, diffuse
			   and specular lighting calculations are based on the
			   actual  location  of	 the light in eye coordinates,
			   and attenuation is enabled.	The  initial  position
			   is  (0, 0, 1, 0); thus, the initial light source is
			   directional, parallel to, and in the	 direction  of
			   the −z axis.

       GL_SPOT_DIRECTION   params  contains  three  integer  or floating-point
			   values that specify the direction of the  light  in
			   homogeneous	object	coordinates.  Both integer and
			   floating-point values are mapped directly.  Neither
			   integer nor floating-point values are clamped.

			   The spot direction is transformed by the inverse of
			   the modelview matrix when glLight is	 called	 (just
			   as  if  it  were a normal), and it is stored in eye
			   coordinates.	   It	is   significant   only	  when
			   GL_SPOT_CUTOFF  is  not 180, which it is initially.
			   The initial direction is (0, 0, -1).

       GL_SPOT_EXPONENT	   params is a single integer or floating-point	 value
			   that	 specifies  the	 intensity distribution of the
			   light.   Integer  and  floating-point  values   are
			   mapped  directly.  Only values in the range [0,128]
			   are accepted.

			   Effective light  intensity  is  attenuated  by  the
			   cosine  of  the  angle between the direction of the
			   light and the direction from the light to the  ver‐
			   tex	being lighted, raised to the power of the spot
			   exponent.  Thus, higher spot exponents result in  a
			   more	 focused  light source, regardless of the spot
			   cutoff angle (see GL_SPOT_CUTOFF, next  paragraph).
			   The	initial	 spot exponent is 0, resulting in uni‐
			   form light distribution.

       GL_SPOT_CUTOFF	   params is a single integer or floating-point	 value
			   that	 specifies the maximum spread angle of a light
			   source.   Integer  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	inten‐
			   sity	 is  controlled	 by  the spot exponent and the
			   attenuation factors.	 The initial  spot  cutoff  is
			   180, resulting in uniform light distribution.

       GL_CONSTANT_ATTENUATION

       GL_LINEAR_ATTENUATION

       GL_QUADRATIC_ATTENUATION
			   params  is a single integer or floating-point value
			   that specifies one of the three  light  attenuation
			   factors.   Integer  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), result‐
			   ing in no attenuation.

NOTES
       It is always the case that GL_LIGHTi = GL_LIGHT0 + i.

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

       GL_INVALID_VALUE	 is  generated	if  a spot exponent value is specified
       outside the range [0,128], or if spot cutoff is specified  outside  the
       range  [0,90]  (except  for  the	 special  value 180), or if a negative
       attenuation factor is specified.

       GL_INVALID_OPERATION is generated if glLight is	executed  between  the
       execution of glBegin and the corresponding execution of glEnd.

ASSOCIATED GETS
       glGetLight
       glIsEnabled with argument GL_LIGHTING

SEE ALSO
       glColorMaterial(3G), glLightModel(3G), glMaterial(3G)

								   GLLIGHT(3G)
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