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GLLIGHTMODEL(3gl)					     GLLIGHTMODEL(3gl)

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   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_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 parame‐
       ter 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 posi‐
		 tive 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 spec‐
		 ifies 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 coordi‐
		 nates.	 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 spec‐
		 ifies	whether	 one-  or  two-sided lighting calculations are
		 done for polygons.  It has no effect on the lighting calcula‐
		 tions	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.  Oth‐
		 erwise, two-sided lighting is specified.  In this case,  ver‐
		 tices	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  parame‐
		 ters,	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  normal‐
       ized  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 contri‐
       butions 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.

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

       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_LOCAL_VIEWER
       glGet with argument GL_LIGHT_MODEL_TWO_SIDE
       glIsEnabled with argument GL_LIGHTING

SEE ALSO
       glLight, glMaterial

				   15 Mar 97		     GLLIGHTMODEL(3gl)
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