Function validateAndCleanGeometry

js/stlLoader.js:50–102

* Scan a non-indexed geometry's position array and remove: * - triangles with any non-finite (NaN / ±Infinity) coordinate * - degenerate triangles whose area is below 1e-12 mm² * * Operates in-place by compacting the Float32Array and replacing the * BufferAttribute. Any existing normal attr

(geometry)

 *
 * Operates in-place by compacting the Float32Array and replacing the
 * BufferAttribute. Any existing normal attribute is deleted so that
 * setupGeometry will recompute it on the clean data.
 *
 * Returns { nanCount, degenerateCount } so callers can warn the user.
 */
function validateAndCleanGeometry(geometry) {
  const pos  = geometry.attributes.position;
  const src  = pos.array;           // Float32Array, 9 floats per triangle
  const triCount = src.length / 9;

  let writeIdx = 0;
  let nanCount = 0;
  let degenerateCount = 0;

  for (let t = 0; t < triCount; t++) {
    const b  = t * 9;
    const ax = src[b],   ay = src[b+1], az = src[b+2];
    const bx = src[b+3], by = src[b+4], bz = src[b+5];
    const cx = src[b+6], cy = src[b+7], cz = src[b+8];

    if (!isFinite(ax) || !isFinite(ay) || !isFinite(az) ||
        !isFinite(bx) || !isFinite(by) || !isFinite(bz) ||
        !isFinite(cx) || !isFinite(cy) || !isFinite(cz)) {
      nanCount++;
      continue;
    }

    // Cross product of (B−A) × (C−A); skip if area² < 1e-24 (area < 1e-12)
    const ux = bx-ax, uy = by-ay, uz = bz-az;
    const vx = cx-ax, vy = cy-ay, vz = cz-az;
    const area2 = (uy*vz-uz*vy)**2 + (uz*vx-ux*vz)**2 + (ux*vy-uy*vx)**2;
    if (area2 < 1e-24) {
      degenerateCount++;
      continue;
    }

    if (writeIdx !== b) {
      src[writeIdx]   = ax; src[writeIdx+1] = ay; src[writeIdx+2] = az;
      src[writeIdx+3] = bx; src[writeIdx+4] = by; src[writeIdx+5] = bz;
      src[writeIdx+6] = cx; src[writeIdx+7] = cy; src[writeIdx+8] = cz;
    }
    writeIdx += 9;
  }

  const removed = nanCount + degenerateCount;
  if (removed > 0) {
    geometry.setAttribute('position', new THREE.BufferAttribute(src.slice(0, writeIdx), 3));
    geometry.deleteAttribute('normal'); // stale — recomputed below
  }

  if (writeIdx === 0) {
    throw new Error(
      `All ${triCount} triangles in the mesh are invalid (${nanCount} NaN, ${degenerateCount} degenerate). Cannot load file.`
    );
  }