yawn/server/web/assets/sculpt/topology.test.js

import assert from "node:assert/strict";
import test from "node:test";

import { buildMesh } from "./mesh.js";
import {
  MAX_TRIANGLES,
  MAX_VERTICES,
  decimate,
  preset,
  subdivide,
} from "./topology.js";

function inspect(mesh) {
  const edges = new Map();
  let volume = 0;
  for (let k = 0; k < mesh.indices.length; k += 3) {
    const face = Array.from(mesh.indices.subarray(k, k + 3));
    assert.equal(new Set(face).size, 3);
    const [a, b, c] = face;
    const p = mesh.positions;
    volume +=
      (p[a * 3] * (p[b * 3 + 1] * p[c * 3 + 2] - p[b * 3 + 2] * p[c * 3 + 1]) +
        p[a * 3 + 1] * (p[b * 3 + 2] * p[c * 3] - p[b * 3] * p[c * 3 + 2]) +
        p[a * 3 + 2] * (p[b * 3] * p[c * 3 + 1] - p[b * 3 + 1] * p[c * 3])) /
      6;
    for (const [x, y] of [
      [a, b],
      [b, c],
      [c, a],
    ]) {
      const key = x < y ? `${x},${y}` : `${y},${x}`;
      edges.set(key, (edges.get(key) || 0) + 1);
    }
  }
  assert.ok([...mesh.positions, ...mesh.normals].every(Number.isFinite));
  assert.ok([...edges.values()].every((count) => count === 2));
  assert.ok(
    volume > 0,
    `expected outward winding, signed volume was ${volume}`,
  );
}

test("presets are bounded, outward, closed manifold meshes", () => {
  for (const name of ["sphere", "cube", "cylinder", "cone", "torus"]) {
    const mesh = preset(name);
    assert.ok(mesh.positions.length / 3 <= MAX_VERTICES);
    assert.ok(mesh.indices.length / 3 <= MAX_TRIANGLES);
    assert.ok(mesh.indices.length / 3 >= 2000);
    assert.equal(mesh.masks.length, mesh.positions.length / 3);
    inspect(mesh);
  }
});

test("subdivision shares midpoints and interpolates masks without changing winding", () => {
  const tetra = buildMesh(
    [1, 1, 1, -1, -1, 1, -1, 1, -1, 1, -1, -1],
    [0, 2, 1, 0, 1, 3, 0, 3, 2, 1, 2, 3],
    0,
    [0, 1, 0.5, 0],
  );
  const result = subdivide(tetra);
  assert.equal(result.indices.length, tetra.indices.length * 4);
  assert.equal(result.positions.length / 3, 10); // 4 vertices + 6 unique edges.
  const midpoint =
    Array.from(result.positions).findIndex(
      (_, k, p) =>
        k % 3 === 0 && p[k] === 0 && p[k + 1] === 0 && p[k + 2] === 1,
    ) / 3;
  assert.equal(result.masks[midpoint], 0.5);
  assert.deepEqual(
    Array.from(result.positions.slice(0, 12)),
    Array.from(tetra.positions),
  );
  inspect(result);
});

test("decimation keeps a closed mesh and protects masked neighborhoods", () => {
  const source = preset("sphere", 4);
  source.masks[0] = 1;
  const protectedFaces = Array.from(source.incident[0], (f) =>
    Array.from(source.indices.slice(f * 3, f * 3 + 3)).map((v) =>
      Array.from(source.positions.slice(v * 3, v * 3 + 3)).join(","),
    ),
  );
  const result = decimate(source, 0.75);
  assert.ok(result.indices.length < source.indices.length);
  inspect(result);
  const coordinates = new Set();
  for (let v = 0; v < result.positions.length / 3; v++)
    coordinates.add(
      Array.from(result.positions.slice(v * 3, v * 3 + 3)).join(","),
    );
  assert.ok(protectedFaces.flat().every((point) => coordinates.has(point)));
  assert.equal([...result.masks].filter(Boolean).length, 1);
});

test("fully masked decimation is a no-op", () => {
  const source = preset("torus", 2);
  source.masks.fill(1);
  const result = decimate(source, 0.25);
  assert.deepEqual(result.indices, source.indices);
  assert.deepEqual(result.positions, source.positions);
  assert.deepEqual(result.masks, source.masks);
});

test("subdivision rejects cap overflow before allocating output", () => {
  const positions = new Float32Array((MAX_VERTICES - 1) * 3);
  const mesh = buildMesh(positions, new Uint32Array([0, 1, 2]));
  assert.throws(() => subdivide(mesh), /limits/);
});