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vpScanlineNormals(3) Library Functions Manual vpScanlineNormals(3) NAME vpScanlineNormals - compute surface normal vectors and gradient magni- tudes 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 di- rection. scalar_plus_y 1D array of scalar samples adjacent to scalar_data in the +Y di- rection. scalar_minus_z 1D array of scalar samples adjacent to scalar_data in the -Z di- rection. scalar_plus_z 1D array of scalar samples adjacent to scalar_data in the +Z di- rection. 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 en- coded 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)). vp- ScanlineNormals is useful for loading large volumes into memory scan- line-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 func- tion 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. vpScanli- neNormals 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 call- ing 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 con- stant VP_SKIP_FIELD, in which case the corresponding quantity is not computed or copied. The voxel fields for the scalar value and the gra- dient 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 vpNormalIn- dex(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) VolPack vpScanlineNormals(3)
NAME | SYNOPSIS | ARGUMENTS | DESCRIPTION | ERRORS | SEE ALSO
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