fglLightModel(3G)

NAME
     fglLightModelf, fglLightModeli, fglLightModelfv, fglLightModeliv - set
     the lighting model parameters


FORTRAN SPECIFICATION
     SUBROUTINE fglLightModelf( INTEGER*4 pname,
                                REAL*4 param )
     SUBROUTINE fglLightModeli( INTEGER*4 pname,
                                INTEGER*4 param )


PARAMETERS
     pname   Specifies a single-valued lighting model parameter.
             GL_LIGHT_MODEL_LOCAL_VIEWER and GL_LIGHT_MODEL_TWO_SIDE are
             accepted.

     param   Specifies the value that param will be set to.

FORTRAN SPECIFICATION
     SUBROUTINE fglLightModelfv( INTEGER*4 pname,
                                 CHARACTER*8 params )
     SUBROUTINE fglLightModeliv( INTEGER*4 pname,
                                 CHARACTER*8 params )


PARAMETERS
     pname
          Specifies a lighting model parameter.  GL_LIGHT_MODEL_AMBIENT,
          GL_LIGHT_MODEL_LOCAL_VIEWER, and GL_LIGHT_MODEL_TWO_SIDE are
          accepted.

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

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

     GL_LIGHT_MODEL_AMBIENT
               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_LIGHT_MODEL_LOCAL_VIEWER
               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 vertex in eye
               coordinates.  Otherwise, specular reflections are computed from
               the origin of the eye coordinate system.  The initial value is
               0.

     GL_LIGHT_MODEL_TWO_SIDE
               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 vertex 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 vertex's normal with the normalized
     vector from the vertex 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
     vertex-to-eye and vertex-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 vertex 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 vertex ranges
     from the ambient to the specular values passed to fglMaterial 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 fglLightModel is executed between
     the execution of fglBegin and the corresponding execution of fglEnd.

ASSOCIATED GETS
     fglGet with argument GL_LIGHT_MODEL_AMBIENT
     fglGet with argument GL_LIGHT_MODEL_LOCAL_VIEWER
     fglGet with argument GL_LIGHT_MODEL_TWO_SIDE
     fglIsEnabled with argument GL_LIGHTING


SEE ALSO
     fglLight, fglMaterial