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vpSetMaterial(3)	   Library Functions Manual	      vpSetMaterial(3)

NAME
       vpSetMaterial - set material properties

SYNOPSIS
       #include	<volpack.h>

       vpResult
       vpSetMaterial(vpc, material, property, surface_side, r, g, b)
	   vpContext *vpc;
	   int material;
	   int property;
	   int surface_side;
	   double r, g,	b;

ARGUMENTS
       vpc    VolPack context from vpCreateContext.

       material
	      A	 constant  specifying  a particular material number (VP_MATER-
	      IAL0, VP_MATERIAL1, ..., VP_MATERIAL5).

       property
	      A	constant specifying one	material property (VP_AMBIENT, VP_DIF-
	      FUSE, VP_SPECULAR	or VP_SHINYNESS).

       surface_side
	      A	constant specifying which side of  the	material  surface  the
	      properties apply to (VP_EXTERIOR,	VP_INTERIOR or VP_BOTH_SIDES).

       r, g, b
	      RGB  components  of the color associated with the	property.  For
	      VP_SHINYNESS, g and b are	not used.

DESCRIPTION
       vpSetMaterial is	used to	set the	properties of a	material  type.	  Each
       voxel may be composed of	a mixture of several different material	types,
       as  described  in vpSetLookupShader(3).	Each material type has its own
       color and light reflection properties.  The properties are used as  pa-
       rameters	 to  the Phong shading equation	for computing the color	of the
       material	given a	set of light sources and a viewing direction (see  vp-
       ShadeTable(3)).

       To  initialize  the  material  parameters,  call	vpSetMaterial for each
       property	of each	material type to be used.  The total number of materi-
       als is specified	as an argument to vpSetLookupShader.  The first	mater-
       ial is specified	by the constant	VP_MATERIAL0, the second is  VP_MATER-
       IAL1, and so on.

       The VP_AMBIENT property specifies the RGB ambient light coefficients of
       the  material.	This term represents the intensity of background light
       reflected by the	material.  Each	of the RGB  components	specifies  the
       coefficient  for	the corresponding light	basis function.	 The values of
       the coefficients	should be in the range 0.0-1.0.	 Default: 0.1

       The VP_DIFFUSE property specifies the RGB diffuse light coefficients of
       the material.  This term	represents the fraction	of incident light  in-
       tensity	that  is  reflected diffusely (with a dull, matte appearance).
       The values of the coefficients should be	in  the	 range	0.0-1.0.   De-
       fault: 0.4

       The  VP_SPECULAR	property specifies the RGB specular light coefficients
       of the material.	 This term represents the fraction of  incident	 light
       intensity  that	is reflected specularly	(with a	shiny, mirror-like ap-
       pearance).  The values of the  coefficients  should  be	in  the	 range
       0.0-1.0.	 Default: 0.5

       The VP_SHINYNESS	property specifies a single exponent that modifies the
       spread  of specular highlights.	The higher the number, the smaller and
       more intense the	specular highlights.  The exponent is  specified  with
       the  r  argument	 and can have any value; the generally-useful range is
       1.0 to 100.0.  The g and	b arguments are	 ignored  for  this  property.
       Default:	10.0

       The  surface_side argument specifies which side of the material surface
       the properties apply to.	 By default, the "interior" side of a voxel is
       the side	in the direction of the	surface	normal.	 During	rendering,  if
       the  normal points closer to the	direction of the viewer	than the oppo-
       site of the normal then the viewer is looking at	the exterior  side  of
       the  voxel rather than the interior.  Different material	parameters can
       be applied to the two surface sides by calling vpSetMaterial separately
       for each	side.  The option VP_BOTH_SIDES	allows the same	property to be
       set for both sides with only one	function call.	It is possible to  re-
       verse the definition of interior	and exterior sides by calling vpEnable
       with the	VP_REVERSE_SURFACE_SIDES option.

       Voxels  are  shaded  using  the	following  equation:  I	= A + L	* (D *
       n_dot_l + S * pow(n_dot_h, E))

       I	   intensity for one color channel
       A	   ambient intensity coefficient
       D	   diffuse reflection coefficient
       S	   specular reflection coefficient
       E	   shinyness
       L	   light intensity
       n_dot_l	   dot product of normal and light vectors
       n_dot_h	   dot product of normal and highlight vectors	This  equation
       is  evaluated  separately  for  each  color channel.  If	multiple light
       sources are enabled an additional term identical	 to  the  second  term
       above  is  added	 for  each  light source (with different values	for L,
       n_dot_l and n_dot_h corresponding to the	particular light source).

STATE VARIABLES
       Information about the current material properties can be	retrieved with
       the following state variable codes (see vpGeti(3)):  VP_MATERIAL_COUNT,
       VP_REVERSE_SURFACE_SIDES

ERRORS
       The  normal  return  value is VP_OK.  The following error return	values
       are possible:

       VPERROR_BAD_VALUE
	      Either the material number or the	RGB components are invalid.

       VPERROR_BAD_OPTION
	      Either the surface_side or property arguments are	invalid.

SEE ALSO
       VolPack(3), vpCreateContext(3), vpSetLookupShader(3),  vpShadeTable(3),
       vpGetMaterial(3)

VolPack							      vpSetMaterial(3)

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