MirOS Manual: glLightModel(3), glLightModelf(3), glLightModelfv(3), glLightModeli(3), glLightModeliv(3)


GLLIGHTMODEL(3G)    UNIX Programmer's Manual     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

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               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 com-
               putation 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 equa-
               tion. 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 nor-
               mals. 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

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     dot product of the vertex's normal with the normalized vec-
     tor 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 exe-
     cuted 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)

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