1vpOctreeMask(3) Library Functions Manual vpOctreeMask(3)
2
6 vpOctreeMask - compute a mask representing one level of a min-max
7 octree
8
10 #include <volpack.h>
11 vpResult
13 vpOctreeMask(vpc, array, array_size, max_level)
14 vpContext *vpc;
15 unsigned char *array;
16 int array_size;
17 int max_level;
18
20 vpc VolPack context from vpCreateContext.
21 array A 3D array for storing the mask.
23 array_size
25 Size of array in bytes.
26 max_level
28 Maximum octree level to descend to.
29
31 vpOctreeMask is used for performance debugging when rendering volumes
32 with a min-max octree. During rendering the min-max octree is used to
33 help determine which voxels are transparent. The time required to make
34 this determination can be minimized by an appropriate choice for the
35 range parameters for vpMinMaxOctreeThreshold and the node size parame‐
36 ters for vpCreateMinMaxOctree. vpOctreeMask provides information that
37 can help to determine whether a set of parameters works effectively or
38 not.
39 The output of the routine is stored in a 3D array of bytes that has the
41 same dimensions as the volume (although each element is only one byte,
42 regardless of the size of a voxel). For each voxel in the volume the
43 corresponding byte in the output array is set by vpOctreeMask to one of
44 three values: 0 if the voxel is definitely transparent, 255 if the
45 voxel may be non-transparent, or 128 if the voxel may be non-transpar‐
46 ent and there is more detailed information available at unvisited lev‐
47 els of the octree. The max_level argument specifies the deepest level
48 of the octree to be visited (the root level is level 0).
49 A suggested way to use this routine is to compute an octree using a
51 particular set of parameters and then call vpOctreeMask with several
52 different values for max_level. For each resulting mask array, look at
53 slices (or create a volume rendering!) and see how accurately the mask
54 captures the general shape of the data in the original volume. The
55 best set of parameters results in a mask that captures the general
56 shape without an excessively small value for the minimum octree node
57 size (which would result in a very large data structure and a lot of
58 traversal overhead).
59
61 The normal return value is VP_OK. The following error return values
62 are possible:
63 VPERROR_BAD_SIZE
65 There is no octree or the output array has the wrong size.
66 VPERROR_BAD_VOXEL
68 The voxel size or the voxel fields have not been specified or
69 have been incorrectly specified.
70 VPERROR_BAD_CLASSIFIER
72 The opacity transfer function tables have invalid sizes or are
73 associated with invalid voxel fields or have been incorrectly
74 specified.
75
77 VolPack(3), vpCreateContext(3), vpCreateMinMaxOctree(3)
78VolPack vpOctreeMask(3)