vpOctreeMask(3) Library Functions Manual vpOctreeMask(3) NAME vpOctreeMask - compute a mask representing one level of a min-max octree SYNOPSIS #include <volpack.h> vpResult vpOctreeMask(vpc, array, array_size, max_level) vpContext *vpc; unsigned char *array; int array_size; int max_level; ARGUMENTS vpc VolPack context from vpCreateContext. array A 3D array for storing the mask. array_size Size of array in bytes. max_level Maximum octree level to descend to. DESCRIPTION vpOctreeMask is used for performance debugging when rendering volumes with a min-max octree. During rendering the min-max octree is used to help de- termine which voxels are transparent. The time required to make this de- termination can be minimized by an appropriate choice for the range parame- ters for vpMinMaxOctreeThreshold and the node size parameters for vpCre- ateMinMaxOctree. vpOctreeMask provides information that can help to deter- mine whether a set of parameters works effectively or not. The output of the routine is stored in a 3D array of bytes that has the same dimensions as the volume (although each element is only one byte, re- gardless of the size of a voxel). For each voxel in the volume the corre- sponding byte in the output array is set by vpOctreeMask to one of three values: 0 if the voxel is definitely transparent, 255 if the voxel may be non-transparent, or 128 if the voxel may be non-transparent and there is more detailed information available at unvisited levels of the octree. The max_level argument specifies the deepest level of the octree to be visited (the root level is level 0). A suggested way to use this routine is to compute an octree using a partic- ular set of parameters and then call vpOctreeMask with several different values for max_level. For each resulting mask array, look at slices (or create a volume rendering!) and see how accurately the mask captures the general shape of the data in the original volume. The best set of parame- ters results in a mask that captures the general shape without an exces- sively small value for the minimum octree node size (which would result in a very large data structure and a lot of traversal overhead). ERRORS The normal return value is VP_OK. The following error return values are possible: VPERROR_BAD_SIZE There is no octree or the output array has the wrong size. VPERROR_BAD_VOXEL The voxel size or the voxel fields have not been specified or have been incorrectly specified. VPERROR_BAD_CLASSIFIER The opacity transfer function tables have invalid sizes or are asso- ciated with invalid voxel fields or have been incorrectly specified. SEE ALSO VolPack(3), vpCreateContext(3), vpCreateMinMaxOctree(3) VolPack vpOctreeMask(3)
NAME | SYNOPSIS | ARGUMENTS | DESCRIPTION | ERRORS | SEE ALSO
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