NAME

       vpNormalIndex, vpNormal - encode/decode a surface normal vector

SYNOPSIS

       #include <volpack.h>

       int
       vpNormalIndex(nx, ny, nz)
           double nx, ny, nz;

       vpResult
       vpNormal(n, nx_ptr, ny_ptr, nz_ptr)
           int n;
           double *nx_ptr, *ny_ptr, *nz_ptr;

ARGUMENTS

       nx     X component of surface normal vector.

       ny     Y component of surface normal vector.

       nz     Z component of surface normal vector.

       n      Encoded surface normal vector.

       nx_ptr Pointer to storage for returning X component of surface normal vector.

       ny_ptr Pointer to storage for returning Y component of surface normal vector.

       nz_ptr Pointer to storage for returning Z component of surface normal vector.

DESCRIPTION

       These  two  routines  are used to convert surface normal vectors between encoded and unencoded forms.  An
       unencoded vector is described by its three components (stored as double-precision floating point numbers)
       in an orthogonal coordinate system.  An encoded vector is described by a single integer that is  suitable
       for  use  as  an index in a shading lookup table.  VolPack's built-in shading routines require the use of
       surface normal vectors encoded using vpNormalIndex (or one of the higher-level normal vector  computation
       routines,  vpVolumeNormals or vpScanlineNormals).  User-defined shading routines or lookup tables are not
       required to use encoded normal vectors.

       vpNormalIndex computes an encoded vector from the components of an unencoded vector.  The vector must  be
       normalized  (nx*nx + ny*ny + nz*nz = 1).  The maximum possible value of an encoded normal is given by the
       constant VP_NORM_MAX.

       vpNormal computes the components of a vector from the encoded integer form.  The encoded normal has  less
       resolution  than  the unencoded form, so the vector computed by vpNormal may not be equal to the original
       vector passed to vpNormalIndex.

ERRORS

       vpNormalIndex always returns a valid encoded normal vector.

       vpNormal normally returns the value VP_OK.  The following return value is possible:

       VPERROR_BAD_VALUE
              The encoded normal vector is invalid.

SEE ALSO

       VolPack(3), vpVolumeNormals(3), vpScanlineNormals(3)

VolPack                                                                                         vpNormalIndex(3)