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vpShadeTable(3)		   Library Functions Manual	       vpShadeTable(3)

NAME
       vpShadeTable - compute the contents of the shading lookup table

SYNOPSIS
       #include	<volpack.h>

       vpResult
       vpShadeTable(vpc)
	   vpContext *vpc;

ARGUMENTS
       vpc    VolPack context from vpCreateContext.

DESCRIPTION
       vpShadeTable  computes  the contents of the shading lookup table	previ-
       ously specified with vpLookupShader.  For each entry in the table,  the
       Phong  shading equation is evaluated using the current lighting proper-
       ties (as	specified with vpSetLight), material properties	(as  specified
       with vpSetMaterial), and	viewing	parameters (as specified with the view
       transformation commands).  See vpSetMaterial(3) for  a  description  of
       the shading calculation.

       This  function should be	called before rendering	a volume if any	of the
       lighting	or material properties have changed or if  the	viewpoint  has
       changed	since  the last	call to	vpShadeTable.  It should not be	called
       if shading is performed using a callback	function  or  if  the  shading
       lookup tables are initialized by	a user-defined routine.

       There is	one state variable that	affects	the operation of vpShadeTable.
       If VP_CLAMP_SHADE_TABLE is enabled (see vpEnable(3)), then  values  are
       clamped to the range 0.0-255.0 before they are stored in	the table.  If
       this option is not enabled then no clamping is performed.  Clamping  is
       enabled	by  default, but can be	turned off to achieve special effects.
       For example, if all of the voxels in a data set have very  low  opacity
       then the	rendered image may be very dark.  To brighten it, multiply all
       of the material parameter coefficients by a constant,  possibly	making
       the values exceed 1.0, and turn off clamping.

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

       VPERROR_SINGULAR
	      One of the current view transformation matrices is singular.

       VPERROR_BAD_SHADER
	      The shading lookup tables	are sized incorrectly, or one  of  the
	      voxel  fields used to index the tables is	invalid, or the	number
	      of material types	is invalid.

       VPERROR_BAD_SHADOW
	      The angle	between	the shadow light vector	and the	viewing	direc-
	      tion is too large	(must be less than 45 degrees).	 Either	change
	      the light	direction or disable shadows  (see  vpSetShadowLookup-
	      Shader).

SEE ALSO
       VolPack(3),    vpCreateContext(3),   vpCurrentMatrix(3),	  vpSetLookup-
       Shader(3), vpSetLight(3), vpSetMaterial(3)

VolPack							       vpShadeTable(3)

NAME | SYNOPSIS | ARGUMENTS | DESCRIPTION | ERRORS | SEE ALSO

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