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GLLIGHTMODEL(3G)                                                                            GLLIGHTMODEL(3G)



NAME
       glLightModelf, glLightModeli, glLightModelfv, glLightModeliv - set the lighting model parameters


C SPECIFICATION
       void glLightModelf( GLenum pname,
                           GLfloat param )
       void glLightModeli( GLenum pname,
                           GLint param )


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

       param   Specifies the value that param will be set to.

C SPECIFICATION
       void glLightModelfv( GLenum pname,
                            const GLfloat *params )
       void glLightModeliv( GLenum pname,
                            const GLint *params )


PARAMETERS
       pname  Specifies a lighting model parameter.   GL_LIGHT_MODEL_AMBIENT,  GL_LIGHT_MODEL_COLOR_CONTROL,
              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
       glLightModel  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  inten-sity intensity
                 sity  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_COLOR_CONTROL
                 params must be either GL_SEPARATE_SPECULAR_COLOR or GL_SINGLE_COLOR.  GL_SINGLE_COLOR spec-ifies specifies
                 ifies  that  a  single  color  is  generated  from  the  lighting computation for a vertex.
                 GL_SEPARATE_SPECULAR_COLOR specifies that the specular color  computation  of  lighting  be
                 stored  separately  from  the remainder of the lighting computation.  The specular color is
                 summed into the generated fragment's color after the application  of  texture  mapping  (if
                 enabled).  The initial value is GL_SINGLE_COLOR.

       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 twosided
                 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  prod-uct product
       uct  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 specu-lar specular
       lar values passed to glMaterial 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.

NOTES
       GL_LIGHT_MODEL_COLOR_CONTROL is available only if the GL version is 1.2 or greater.

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

       GL_INVALID_ENUM  is  generated  if  pname  is  GL_LIGHT_MODEL_COLOR_CONTROL  and params is not one of
       GL_SINGLE_COLOR or GL_SEPARATE_SPECULAR_COLOR.

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

ASSOCIATED GETS
       glGet with argument GL_LIGHT_MODEL_AMBIENT
       glGet with argument GL_LIGHT_MODEL_COLOR_CONTROL
       glGet with argument GL_LIGHT_MODEL_LOCAL_VIEWER
       glGet with argument GL_LIGHT_MODEL_TWO_SIDE
       glIsEnabled with argument GL_LIGHTING

SEE ALSO
       glLight(3G), glMaterial(3G)




                                                                                            GLLIGHTMODEL(3G)