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)