fglFragmentLight(3G)

NAME
     fglFragmentLightfSGIX, fglFragmentLightiSGIX, fglFragmentLightfvSGIX,
     fglFragmentLightivSGIX - set fragment light source parameters


FORTRAN SPECIFICATION
     SUBROUTINE fglFragmentLightfSGIX( INTEGER*4 light,
                                       INTEGER*4 pname,
                                       REAL*4 param )
     SUBROUTINE fglFragmentLightiSGIX( INTEGER*4 light,
                                       INTEGER*4 pname,
                                       INTEGER*4 param )


PARAMETERS
     light   Specifies a fragment light.  The number of fragment lights
             depends on the implementation.  They are identified by names of
             the form GL_FRAGMENT_LIGHTi_SGIX where 0 < i <
             GL_MAX_FRAGMENT_LIGHTS_SGIX.

     pname   Specifies a single-valued fragment 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 fragment light source
             light will be set to.

FORTRAN SPECIFICATION
     SUBROUTINE fglFragmentLightfvSGIX( INTEGER*4 light,
                                        INTEGER*4 pname,
                                        CHARACTER*8 params )
     SUBROUTINE fglFragmentLightivSGIX( INTEGER*4 light,
                                        INTEGER*4 pname,
                                        CHARACTER*8 params )


PARAMETERS
     light
          Specifies a fragment light.  The number of fragment lights depends
          on the implementation.  They are identified by names of the form
          GL_FRAGMENT_LIGHTi_SGIX where 0 < i < GL_MAX_FRAGMENT_LIGHTS_SGIX.

     pname
          Specifies a fragment 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
          fragment light source light will be set to.
DESCRIPTION
     fglFragmentLight sets the values of individual fragment light source
     parameters.  light names the fragment light and is a symbolic name of the
     form GL_FRAGMENT_LIGHTi_SGIX, where 0 < i < GL_MAX_FRAGMENT_LIGHTS_SGIX.
     pname specifies one of ten fragment 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 fragment lighting calculation, call fglEnable and
     fglDisable with argument GL_FRAGMENT_LIGHTING_SGIX. Fragment lighting is
     initially disabled.  When it is enabled, light sources that are enabled
     contribute to the fragment lighting calculation.  Fragment light source i
     is enabled and disabled using fglEnable and fglDisable with argument
     GL_FRAGMENT_LIGHTi_SGIX.

     The ten fragment light parameters are as follows:

     GL_AMBIENT          params contains four integer or floating-point values
                         that specify the ambient RGBA intensity of the
                         fragment 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 values
                         are clamped.  The initial ambient fragment 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
                         fragment 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 values
                         are clamped.  The initial value for
                         GL_FRAGMENT_LIGHT0_SGIX is (1, 1, 1, 1); for other
                         fragment 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
                         fragment 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 values
                         are clamped.  The initial value for
                         GL_FRAGMENT_LIGHT0_SGIX is (1, 1, 1, 1); for other
                         fragment 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 fragment 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 fglFragmentLight 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 fragment light
                         is treated as a directional source.  Diffuse and
                         specular fragment lighting calculations take the
                         light's direction, but not its actual position, into
                         account, and attenuation is disabled.  Otherwise,
                         diffuse and specular fragment lighting calculations
                         are based on the actual location of the fragment
                         light in eye coordinates, and attenuation is enabled.
                         The initial position is (0, 0, 1, 0); thus, the
                         initial fragment 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 fragment
                         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 fglFragmentLight 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
                         fragment light.  Integer and floating-point values
                         are mapped directly.  Only values in the range
                         [0,128] are accepted.

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

     GL_SPOT_CUTOFF      params is a single integer or floating-point value
                         that specifies the maximum spread angle of a fragment
                         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 fragment light and the
                         direction from the light to the vertex being lighted
                         is greater than the spot cutoff angle, the fragment
                         light is completely masked.  Otherwise, its intensity
                         is controlled by the spot exponent and the
                         attenuation factors.  The initial spot cutoff is 180,
                         resulting in uniform fragment 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 fragment light
                         attenuation factors.  Integer and floating-point
                         values are mapped directly.  Only nonnegative values
                         are accepted.  If the fragment 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
                         fragment 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_FRAGMENT_LIGHTi_SGIX =
     GL_FRAGMENT_LIGHT0_SGIX + 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 fglFragmentLight is executed between
     the execution of fglBegin and the corresponding execution of fglEnd.

ASSOCIATED GETS
     fglGetFragmentLight
     fglIsEnabled with argument GL_FRAGMENT_LIGHTING_SGIX

MACHINE DEPENDENCIES
     The SGIX_fragment_lighting extension is supported only on Octane2 VPro
     systems.

     On Octane2 VPro systems, use of the texture q coordinate to achieve
     projective texture effects will be processed on a per-vertex basis
     instead of a per-pixel basis, unless the the texture matrix is set up to
     be projective.  (A projective texture matrix is defined to be one in
     which any of the 13th, 14th or 15th elements is non-zero.)  In addition,
     if either two-sided lighting or fragment lighting is in effect,
     projective texture effects will always be processed on a per-vertex
     basis.


SEE ALSO
     fglFragmentColorMaterial, fglFragmentLightModel, fglFragmentMaterial