NAME

       vpScanlineNormals - compute surface normal vectors and gradient magnitudes for a scanline

SYNOPSIS

       #include <volpack.h>

       vpResult
       vpScanlineNormals(vpc, length, scalar_data, scalar_minus_y, scalar_plus_y, scalar_minus_z, scalar_plus_z,
               voxel_data, scalar_field, grad_field, norm_field)
           vpContext *vpc;
           int length;
           unsigned char *scalar_data;
           unsigned char *scalar_minus_y, *scalar_plus_y;
           unsigned char *scalar_minus_z, *scalar_plus_z;
           void *voxel_data;
           int scalar_field;
           int grad_field;
           int norm_field;

ARGUMENTS

       vpc    VolPack context from vpCreateContext.

       length Size of scalar_data array in bytes.

       scalar_data
              1D array of scalar samples.

       scalar_minus_y
              1D array of scalar samples adjacent to scalar_data in the -Y direction.

       scalar_plus_y
              1D array of scalar samples adjacent to scalar_data in the +Y direction.

       scalar_minus_z
              1D array of scalar samples adjacent to scalar_data in the -Z direction.

       scalar_plus_z
              1D array of scalar samples adjacent to scalar_data in the +Z direction.

       voxel_data
              1D array of voxels for storing results.

       scalar_field
              Voxel field number indicating the field in which to store the scalar samples.

       grad_field
              Voxel field number indicating the field in which to store the gradient magnitudes  of  the  scalar
              samples.

       norm_field
              Voxel field number indicating the field in which to store encoded surface normal vectors.

DESCRIPTION

       vpScanlineNormals  is  used  to  precompute  values  for  voxel fields used in classification and shading
       algorithms.  The input is a collection of 5 adjacent 1D arrays of scalar values; a  separate  routine  is
       provided  for  processing  a  full 3D array of voxel data (see vpVolumeNormals(3)).  vpScanlineNormals is
       useful for  loading  large  volumes  into  memory  scanline-by-scanline  and  precomputing  voxel  fields
       incrementally,  instead of loading a complete copy of the 3D scalar array in addition to the voxel array.
       In all other respects this routine is identical in function to vpVolumeNormals.

       The 1D scalar arrays must be arrays of 8-bit values (other  sizes  are  not  currently  supported).   The
       length  parameter  indicates  both  the  size  and  the  number of elements in each of the scalar arrays.
       vpScanlineNormals performs the computation described in  vpVolumeNormals(3),  but  only  for  the  single
       scanline  specified  by  scalar_data.  The other four scanline arguments must be the immediately adjacent
       scanlines and are used to compute the gradient.

       The results are stored in the voxel_data array which must have space for the same number of voxels as the
       length  of one scalar scanline.  The size of a voxel must be specified with vpSetVoxelSize before calling
       vpScanlineNormals, but  it  is  not  necessary  to  call  vpSetRawVoxels.   The  arguments  scalar_field,
       grad_field  and norm_field specify which voxel fields the computed quantities should be stored into.  The
       field  numbers  must  correspond  to  appropriately-sized  voxel   fields   previously   specified   with
       vpSetVoxelField.   Any  of  these  arguments  can  be  the  constant  VP_SKIP_FIELD,  in  which  case the
       corresponding quantity is not computed or copied.  The voxel fields for the scalar value and the gradient
       magnitude  must be one-byte fields, and the field for the surface normal vector must be a two-byte field.
       The constants VP_SCALAR_MAX, VP_GRAD_MAX and VP_NORM_MAX give the maximum value that might be  stored  in
       each  field,  respectively.   The  value stored in the surface normal vector field is actually an encoded
       surface normal; see vpNormalIndex(3).

ERRORS

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

       VPERROR_BAD_VALUE
              One or more of the voxel fields specified is invalid, or the corresponding  voxel  field  has  the
              wrong size.

       VPERROR_BAD_VOXEL
              The voxel size or the voxel fields have not been specified or have been incorrectly specified.

SEE ALSO

       VolPack(3),    vpCreateContext(3),    vpNormalIndex(3),    vpVolumeNormals(3),   vpSetClassifierTable(3),
       vpSetLookupShader(3)