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 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_COLOR_CONTROL
               params must be either GL_SEPARATE_SPECULAR_COLOR or
               GL_SINGLE_COLOR.  GL_SINGLE_COLOR specifies 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 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 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


MACHINE DEPENDENCIES
     On Octane2 VPro systems, glLightModel with GL_SEPARATE_SPECULAR_COLOR is
     not compatible with fragment lighting.  If fragment lighting is enabled,
     it will override the separate specular color light model.

     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
     glLight, glMaterial