vpOctreeMask(3)

📦 version 1.0c7, in fedora 43, fedora 44

💖 vpOctreeMask(3) 💖

okay bestie, welcome to the vpOctreeMask page from the VolPack library — it lives in the Library Functions Manual (section 3, iykyk) and it's lowkey one of those nerdy-but-essential little tools that makes your volume rendering not crawl. let's get into it 🫶

✨ NAME ✨

vpOctreeMask — compute a mask representing one level of a min-max octree. yes that's the whole vibe. 🎀

🌸 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 — your VolPack context, the one you got from vpCreateContext. it's giving main character energy, everything needs it. 👑
  • array — a 3D array where the mask gets stored. this is the output, bestie, it's where the magic lands.
  • array_size — size of array, in bytes. tell her how big she is, she deserves to know.
  • max_level — the maximum octree level to descend to. how deep are we going? you decide. 🙈

💅 DESCRIPTION 💅

so vpOctreeMask is your performance debugging bestie — you use it when you're rendering volumes with a min-max octree. during rendering, the min-max octree helps figure out which voxels are transparent. the time it takes to make that determination can be minimized by picking an appropriate choice for the range parameters of vpMinMaxOctreeThreshold and the node size parameters of vpCreateMinMaxOctree. and vpOctreeMask hands you the info that helps you figure out whether a set of parameters is actually working effectively or is just... not. 💀

the output of this routine gets stored in a 3D array of bytes that has the same dimensions as the volume (even though each element is only one byte, no matter how big a voxel is — she's compact like that ✨). for every voxel in the volume, vpOctreeMask sets the corresponding byte in the output array to one of three values:

  • 0 — the voxel is definitely transparent. bye girl, nothing to see here. 🍓
  • 255 — the voxel may be non-transparent. potentially iconic, we're watching her. 👀
  • 128 — the voxel may be non-transparent, and there's more detailed information available at unvisited levels of the octree. she's got layers, fr fr. 🌈

the max_level argument specifies the deepest level of the octree to be visited. heads up: the root level is level 0. don't forget that, it matters. 🧚

🎀 a suggested way to use this 🎀

okay so here's the move, bestie: compute an octree using a particular set of parameters, then call vpOctreeMask with several different values for max_level. for each resulting mask array, look at slices (or — and this is the fun part — 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 parameters results in a mask that captures the general shape without an excessively small value for the minimum octree node size. and why do we not want that tiny node size? because it would result in a very large data structure and a whole lot of traversal overhead. not the vibe. 🙅‍♀️

😭 ERRORS 😭

the normal return value is VP_OK. the following error return values are possible:

  • VPERROR_BAD_SIZE — there's no octree, or the output array has the wrong size. size mismatch behavior, we hate to see it. 💔
  • VPERROR_BAD_VOXEL — the voxel size or the voxel fields haven't been specified, or they've been incorrectly specified. specify your voxels, girl.
  • VPERROR_BAD_CLASSIFIER — the opacity transfer function tables have invalid sizes, or they're associated with invalid voxel fields, or they've been incorrectly specified. the classifier is not passing the vibe check. 🚩

🌟 SEE ALSO 🌟

no cap: this whole page is from the VolPack library, manual section 3, and it's all about vpOctreeMask. go forth and debug your octrees, bestie — you've got this. 💜✨

mwah 💋 — with love, your local Unix girlie, signing off from the VolPack manual 🫶🌸

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