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  man pages->IRIX man pages -> OpenGL/gllightmodel (3)              


glLightModel(3G)	       OpenGL Reference		      glLightModel(3G)

NAME    [Toc]    [Back]

     glLightModelf, glLightModeli, glLightModelfv, glLightModeliv - set	the
     lighting model parameters

C SPECIFICATION    [Toc]    [Back]

     void glLightModelf( GLenum	pname,
			 GLfloat param )
     void glLightModeli( GLenum	pname,
			 GLint param )

PARAMETERS    [Toc]    [Back]

     pname   Specifies a single-valued lighting	model parameter.
	     GL_LIGHT_MODEL_TWO_SIDE are accepted.

     param   Specifies the value that param will be set	to.

C SPECIFICATION    [Toc]    [Back]

     void glLightModelfv( GLenum pname,
			  const	GLfloat	*params	)
     void glLightModeliv( GLenum pname,
			  const	GLint *params )

PARAMETERS    [Toc]    [Back]

	  Specifies a lighting model parameter.	 GL_LIGHT_MODEL_AMBIENT,
	  GL_LIGHT_MODEL_TWO_SIDE are accepted.

	  Specifies a pointer to the value or values that params will be set

DESCRIPTION    [Toc]    [Back]

     glLightModel sets the lighting model parameter.  pname names a parameter
     and params	gives the new value.  There are	three lighting model

     GL_LIGHT_MODEL_AMBIENT    [Toc]    [Back]
	       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).

									Page 1

glLightModel(3G)	       OpenGL Reference		      glLightModel(3G)

     GL_LIGHT_MODEL_COLOR_CONTROL    [Toc]    [Back]
	       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    [Toc]    [Back]
	       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

     GL_LIGHT_MODEL_TWO_SIDE    [Toc]    [Back]
	       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

									Page 2

glLightModel(3G)	       OpenGL Reference		      glLightModel(3G)

     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    [Toc]    [Back]

     GL_LIGHT_MODEL_COLOR_CONTROL is available only if the GL version is 1.2
     or	greater.

ERRORS    [Toc]    [Back]

     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    [Toc]    [Back]

     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

     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 the texture matrix is set	up to
     be	projective.  (A	projective texture matrix is defined to	be one in
     which any of the 13th, 14th or 15th elements is non-zero.)	 In addition,
     if	either two-sided lighting or fragment lighting is in effect,
     projective	texture	effects	will always be processed on a per-vertex

SEE ALSO    [Toc]    [Back]

     glLight, glMaterial

									PPPPaaaaggggeeee 3333
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