fglFragmentLightModel(3G)

NAME
     fglFragmentLightModelfSGIX, fglFragmentLightModeliSGIX,
     fglFragmentLightModelfvSGIX, fglFragmentLightModelivSGIX - set the
     lighting model parameters


FORTRAN SPECIFICATION
     SUBROUTINE fglFragmentLightModelfSGIX( INTEGER*4 pname,
                                            REAL*4 param )
     SUBROUTINE fglFragmentLightModeliSGIX( INTEGER*4 pname,
                                            INTEGER*4 param )


PARAMETERS
     pname   Specifies a single-valued lighting model parameter.
             GL_FRAGMENT_LIGHT_MODEL_LOCAL_VIEWER_SGIX,
             GL_FRAGMENT_LIGHT_MODEL_NORMAL_INTERPOLATION_SGIX, and
             GL_FRAGMENT_LIGHT_MODEL_TWO_SIDE_SGIX are accepted.

     param   Specifies the value that param will be set to.

FORTRAN SPECIFICATION
     SUBROUTINE fglFragmentLightModelfvSGIX( INTEGER*4 pname,
                                             CHARACTER*8 params )
     SUBROUTINE fglFragmentLightModelivSGIX( INTEGER*4 pname,
                                             CHARACTER*8 params )


PARAMETERS
     pname
          Specifies a lighting model parameter.
          GL_FRAGMENT_LIGHT_MODEL_AMBIENT_SGIX,
          GL_FRAGMENT_LIGHT_MODEL_LOCAL_VIEWER_SGIX,
          GL_FRAGMENT_LIGHT_MODEL_NORMAL_INTERPOLATION_SGIX, and
          GL_FRAGMENT_LIGHT_MODEL_TWO_SIDE_SGIX are accepted.

     params
          Specifies a pointer to the value or values that params will be set
          to.

DESCRIPTION
     fglFragmentLightModel sets the lighting model parameter.  pname names a
     parameter and params gives the new value.  There are three lighting model
     parameters:

     GL_FRAGMENT_LIGHT_MODEL_AMBIENT_SGIX
               params contains four integer or floating-point values that
               specify the ambient RGBA intensity of the entire scene.
               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 scene intensity is (0.2, 0.2,
               0.2, 1.0).

     GL_FRAGMENT_LIGHT_MODEL_LOCAL_VIEWER_SGIX
               params is a single integer or floating-point value that
               specifies how specular reflection angles are computed.  If
               params is 0 (or 0.0), specular reflection angles take the view
               direction to be parallel to and in the direction of the -z
               axis, regardless of the location of the fragment in eye
               coordinates.  Otherwise, specular reflections are computed from
               the origin of the eye coordinate system.  The initial value is
               0.

     GL_FRAGMENT_LIGHT_MODEL_NORMAL_INTERPOLATION_SGIX
               params must be either GL_FLAT or GL_SMOOTH, and controls how
               normals are selected for use in the fragment lighting
               computations.  If GL_FLAT is selected for the lighting model,
               the normal from the provoking vertex of the primitive is used
               for all fragment lighting computations.  If GL_SMOOTH is
               specified a normal is computed for each fragment using the
               normals from all of the vertices of the primitive.

     GL_FRAGMENT_LIGHT_MODEL_TWO_SIDE_SGIX
               params is a single integer or floating-point value that
               specifies whether one- or two-sided lighting calculations are
               done for polygons.  It has no effect on the lighting
               calculations for points, lines, or bitmaps.  If params is 0 (or
               0.0), one-sided lighting is specified, and only the front
               material parameters are used in the lighting equation.
               Otherwise, two-sided lighting is specified.  In this case,
               vertices of back-facing polygons are lighted using the back
               material parameters, and have their normals reversed before the
               lighting equation is evaluated.  Vertices of front-facing
               polygons are always lighted using the front material
               parameters, with no change to their normals. The initial value
               is 0.

     In RGBA mode, the lighted color of a fragment is the sum of the material
     emission intensity, the product of the material ambient reflectance and
     the lighting model full-scene ambient intensity, and the contribution of
     each enabled light source.  Each light source contributes the sum of
     three terms:  ambient, diffuse, and specular.  The ambient light source
     contribution is the product of the material ambient reflectance and the
     light's ambient intensity.  The diffuse light source contribution is the
     product of the material diffuse reflectance, the light's diffuse
     intensity, and the dot product of the fragment's normal with the
     normalized vector from the fragment to the light source.  The specular
     light source contribution is the product of the material specular
     reflectance, the light's specular intensity, and the dot product of the
     normalized fragment-to-eye and fragment-to-light vectors, raised to the
     power of the shininess of the material.  All three light source
     contributions are attenuated equally based on the distance from the
     fragment to the light source and on light source direction, spread
     exponent, and spread cutoff angle.  All dot products are replaced with 0
     if they evaluate to a negative value.

     The alpha component of the resulting lighted color is set to the alpha
     value of the material diffuse reflectance.

     In color index mode, the value of the lighted index of a fragment ranges
     from the ambient to the specular values passed to fglFragmentMaterial
     using GL_COLOR_INDEXES.  Diffuse and specular coefficients, computed with
     a (.30, .59, .11) weighting of the lights' colors, the shininess of the
     material, and the same reflection and attenuation equations as in the
     RGBA case, determine how much above ambient the resulting index is.

ERRORS
     GL_INVALID_ENUM is generated if pname is not an accepted value.

     GL_INVALID_OPERATION is generated if fglFragmentLightModel is executed
     between the execution of fglBegin and the corresponding execution of
     fglEnd.

ASSOCIATED GETS
     fglGet with argument GL_FRAGMENT_LIGHT_MODEL_AMBIENT_SGIX
     fglGet with argument GL_FRAGMENT_LIGHT_MODEL_LOCAL_VIEWER_SGIX
     fglGet with argument GL_FRAGMENT_LIGHT_MODEL_NORMAL_INTERPOLATION_SGIX
     fglGet with argument GL_FRAGMENT_LIGHT_MODEL_TWO_SIDE_SGIX
     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 texture matrix is set up to be
     projective.  (A projective texture matrix, specified as 16-element array
     M, is defined to be one in which any of the M[3], M[7], or M[11] array
     elements is non-zero.) In addition, if either two-sided lighting or
     fragment lighting or separate specular lighting is in effect, projective
     texture effects will always be processed on a per-vertex basis.


SEE ALSO
     fglFragmentLight, fglFragmentMaterial