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 implementation, but at least eight lights are supported.  They are identi-
	       fied 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 implementation, but at least eight lights are supported.  They are identi-
	      fied 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 calculation.  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 values 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  repre-
			   sentable value maps to -1.0.  Floating-point values are mapped directly.  Neither integer nor floating-point values are
			   clamped.  The initial ambient light intensity is (0, 0, 0, 1).

       GL_DIFFUSE	   params contains four integer or floating-point values 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 repre-
			   sentable value maps to -1.0.  Floating-point values are mapped directly.  Neither integer 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  contains  four integer or floating-point values 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  repre-
			   sentable value maps to -1.0.  Floating-point values are mapped directly.  Neither integer 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 contains four integer or floating-point values that specify the position 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 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 specular lighting calculations take the light's direction, 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  ini-
			   tially.  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  vertex 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 uniform 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 intensity is controlled by the  spot  expo-
			   nent 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), resulting 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)