Tracking geometry across union and decompose

[neilpa-inv]

I have a bunch of geometries that I'm constructing, some of which overlap, which I union and then decompose to get the disjoint segments. I need to map back to parts that produced those original geometries. Right now I check for a non-empty mesh runIndex pairs and get the associated runOriginalID to map back to my identifiers.

Will this always work and is it the best approach? For context, a minimal example I was experimenting with on the ManifoldCAD.

const {cube, sphere} = Manifold;

const idToIndex = {}

const boxes = [
  // These two will get combined
  cube([10, 2, 1]),
  cube([2, 10, 1]),
  // This one will be different
  cube([3, 3, 1]).translate(5,5)
].map((b, idx) => {
  const uniq = b.asOriginal();
  idToIndex[uniq.originalID()] = idx;
  return uniq;
});

const all = Manifold.union(boxes);

const parts = all.decompose();
// Maps the decomposed parts index back to the indices in the original boxes array
const mapping = new Array(parts.length);

for (let i = 0; i < parts.length; i++) {
  const mesh = parts[i].getMesh();

  mapping[i] = [];
  for (let run = 0; run < mesh.numRun; run++) {
    if (mesh.runIndex[run] !== mesh.runIndex[run+1]) {
      const originalIndex = idToIndex[mesh.runOriginalID[run]];
      mapping[i].push(originalIndex);
    }
  }

  console.log(`decomposed part ${i} contains boxes: [ ${mapping[i].join(',')} ]`)
}

let result = all;

[elalish]

Yup, that's exactly how our IDs are meant to be used. Certainly should always work - if not, please file an issue.