Union Outlines

1// Resolve all overlapping filled regions before extrusion: one boundary per solid.
2import * as THREE from "three/webgpu";
3import Clipper from "../vendor/clipper.cjs";
4const C: any = Clipper,
5  SCALE = 1e6;
6export function unionOutlines(shapes: THREE.Shape[], segments = 24): THREE.Shape[] {
7  const paths: any[] = [];
8  for (const shape of shapes) {
9    for (const [i, ring] of [shape, ...shape.holes].entries()) {
10      const points = ring
11        .getPoints(segments)
12        .map((p) => ({ X: Math.round(p.x * SCALE), Y: Math.round(p.y * SCALE) }));
13      if (points.length < 3) continue;
14      // Nonzero filling adds solids and subtracts holes; overlapping solids do not XOR.
15      if (C.Clipper.Orientation(points) !== (i === 0)) points.reverse();
16      paths.push(points);
17    }
18  }
19  const clipper = new C.Clipper();
20  clipper.StrictlySimple = true;
21  clipper.AddPaths(paths, C.PolyType.ptSubject, true);
22  const tree = new C.PolyTree();
23  clipper.Execute(C.ClipType.ctUnion, tree, C.PolyFillType.pftNonZero, C.PolyFillType.pftNonZero);
24  const result: THREE.Shape[] = [];
25  const pts = (node: any) =>
26    node.Contour().map((p: any) => new THREE.Vector2(p.X / SCALE, p.Y / SCALE));
27  const walk = (node: any) => {
28    for (const child of node.Childs()) {
29      if (!child.IsHole()) {
30        const shape = new THREE.Shape(pts(child));
31        shape.holes = child
32          .Childs()
33          .filter((h: any) => h.IsHole())
34          .map((h: any) => new THREE.Path(pts(h)));
35        result.push(shape);
36      }
37      walk(child);
38    }
39  };
40  walk(tree);
41  return result;
42}