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 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 default 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 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 default 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
	    default 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 zero 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 called between a	call
  to glBegin and the corresponding call	to 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

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Last Edited: Fri Dec 6 11:18:03 EST 1996 by AFV
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