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 previously specified with vpLookupShader.
       For each entry in the table,  the  Phong  shading  equation  is  evaluated  using  the  current  lighting
       properties  (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 direction is too large (must be less
              than   45   degrees).    Either   change   the   light   direction   or   disable   shadows   (see
              vpSetShadowLookupShader).

SEE ALSO

       VolPack(3), vpCreateContext(3), vpCurrentMatrix(3), vpSetLookupShader(3), vpSetLight(3), vpSetMaterial(3)

VolPack                                                                                          vpShadeTable(3)