glLightModel man page on DigitalUNIX

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glLightModel(3G)					      glLightModel(3G)

       glLightModel, glLightModelf, glLightModeli, glLightModelfv, glLightMod‐
       eliv - set the lighting model parameters

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

       Specifies     a	   single-valued     lighting	  model	    parameter.
       GL_LIGHT_MODEL_TWO_SIDE are accepted.  Specifies the value  that	 param
       will be set to.

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

       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 to.

       glLightModel() sets the lighting model parameter.  pname names a param‐
       eter  and  params  gives	 the new value. There are three lighting model
       parameters: 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	float‐
       ing-point  values  are clamped.	The initial ambient scene intensity is
       (0.2, 0.2, 0.2, 1.0).  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_SEPA‐
       RATE_SPECULAR_COLOR  specifies  that  the specular color computation of
       lighting be stored separately from the remainder of the lighting compu‐
       tation.	 The  specular	color  is summed into the generated fragment's
       color after the application of texture mapping (if enabled).  The  ini‐
       tial value is GL_SINGLE_COLOR.  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.  params is a single integer or float‐
       ing-point value that specifies whether one- or two-sided lighting  cal‐
       culations  are done for polygons. It has no effect on the lighting cal‐
       culations 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	speci‐
       fied.  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 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 eval‐
       uate 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.

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

       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().

       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

       glLight(3), glMaterial(3)


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