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 intensity of the entire scene.  Integer  val-
		 ues  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  coordi-
		 nate 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 nor-
		 mals  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

SEE ALSO

       glLight(3G), glMaterial(3G)

																  GLLIGHTMODEL(3G)