1vpScanlineNormals(3) Library Functions Manual vpScanlineNormals(3)
2
6 vpScanlineNormals - compute surface normal vectors and gradient magni‐
7 tudes for a scanline
8
10 #include <volpack.h>
11 vpResult
13 vpScanlineNormals(vpc, length, scalar_data, scalar_minus_y,
14 scalar_plus_y, scalar_minus_z, scalar_plus_z, voxel_data,
15 scalar_field, grad_field, norm_field)
16 vpContext *vpc;
17 int length;
18 unsigned char *scalar_data;
19 unsigned char *scalar_minus_y, *scalar_plus_y;
20 unsigned char *scalar_minus_z, *scalar_plus_z;
21 void *voxel_data;
22 int scalar_field;
23 int grad_field;
24 int norm_field;
25
27 vpc VolPack context from vpCreateContext.
28 length Size of scalar_data array in bytes.
30 scalar_data
32 1D array of scalar samples.
33 scalar_minus_y
35 1D array of scalar samples adjacent to scalar_data in the -Y
36 direction.
37 scalar_plus_y
39 1D array of scalar samples adjacent to scalar_data in the +Y
40 direction.
41 scalar_minus_z
43 1D array of scalar samples adjacent to scalar_data in the -Z
44 direction.
45 scalar_plus_z
47 1D array of scalar samples adjacent to scalar_data in the +Z
48 direction.
49 voxel_data
51 1D array of voxels for storing results.
52 scalar_field
54 Voxel field number indicating the field in which to store the
55 scalar samples.
56 grad_field
58 Voxel field number indicating the field in which to store the
59 gradient magnitudes of the scalar samples.
60 norm_field
62 Voxel field number indicating the field in which to store
63 encoded surface normal vectors.
64
66 vpScanlineNormals is used to precompute values for voxel fields used in
67 classification and shading algorithms. The input is a collection of 5
68 adjacent 1D arrays of scalar values; a separate routine is provided for
69 processing a full 3D array of voxel data (see vpVolumeNormals(3)).
70 vpScanlineNormals is useful for loading large volumes into memory scan‐
71 line-by-scanline and precomputing voxel fields incrementally, instead
72 of loading a complete copy of the 3D scalar array in addition to the
73 voxel array. In all other respects this routine is identical in func‐
74 tion to vpVolumeNormals.
75 The 1D scalar arrays must be arrays of 8-bit values (other sizes are
77 not currently supported). The length parameter indicates both the size
78 and the number of elements in each of the scalar arrays. vpScanli‐
79 neNormals performs the computation described in vpVolumeNormals(3), but
80 only for the single scanline specified by scalar_data. The other four
81 scanline arguments must be the immediately adjacent scanlines and are
82 used to compute the gradient.
83 The results are stored in the voxel_data array which must have space
85 for the same number of voxels as the length of one scalar scanline.
86 The size of a voxel must be specified with vpSetVoxelSize before call‐
87 ing vpScanlineNormals, but it is not necessary to call vpSetRawVoxels.
88 The arguments scalar_field, grad_field and norm_field specify which
89 voxel fields the computed quantities should be stored into. The field
90 numbers must correspond to appropriately-sized voxel fields previously
91 specified with vpSetVoxelField. Any of these arguments can be the con‐
92 stant VP_SKIP_FIELD, in which case the corresponding quantity is not
93 computed or copied. The voxel fields for the scalar value and the gra‐
94 dient magnitude must be one-byte fields, and the field for the surface
95 normal vector must be a two-byte field. The constants VP_SCALAR_MAX,
96 VP_GRAD_MAX and VP_NORM_MAX give the maximum value that might be stored
97 in each field, respectively. The value stored in the surface normal
98 vector field is actually an encoded surface normal; see vpNormalIn‐
99 dex(3).
100
102 The normal return value is VP_OK. The following error return values
103 are possible:
104 VPERROR_BAD_VALUE
106 One or more of the voxel fields specified is invalid, or the
107 corresponding voxel field has the wrong size.
108 VPERROR_BAD_VOXEL
110 The voxel size or the voxel fields have not been specified or
111 have been incorrectly specified.
112
114 VolPack(3), vpCreateContext(3), vpNormalIndex(3), vpVolumeNormals(3),
115 vpSetClassifierTable(3), vpSetLookupShader(3)
116VolPack vpScanlineNormals(3)