filter method Null safety

Implementation

@override
MeshGeometry filter(MeshGeometry mesh) {
  final newAttribs = List<VertexAttrib>.from(mesh.attribs);

  if (mesh.getAttrib('NORMAL') == null) {
    newAttribs.add(VertexAttrib('NORMAL', 3, 'float'));
  }

  final output = MeshGeometry(mesh.triangleVertexCount, newAttribs);

  final p0 = Vector3.zero(), p1 = Vector3.zero(), p2 = Vector3.zero();

  final srcPosition = mesh.getViewForAttrib('POSITION');
  final destPosition = output.getViewForAttrib('POSITION');
  final normals = output.getViewForAttrib('NORMAL');

  if (srcPosition is! Vector3List ||
      destPosition is! Vector3List ||
      normals is! Vector3List) {
    throw UnimplementedError();
  }

  final srcAttribs = <VectorList<Vector>>[];
  final destAttribs = <VectorList<Vector>>[];
  for (var attrib in mesh.attribs) {
    if (attrib.name == 'POSITION' || attrib.name == 'NORMAL') {
      continue;
    }

    srcAttribs.add(mesh.getViewForAttrib(attrib.name)!);
    destAttribs.add(output.getViewForAttrib(attrib.name)!);
  }

  for (var i = 0; i < output.length; i += 3) {
    final i0 = mesh.indices![i];
    final i1 = mesh.indices![i + 1];
    final i2 = mesh.indices![i + 2];

    srcPosition
      ..load(i0, p0)
      ..load(i1, p1)
      ..load(i2, p2);

    destPosition[i] = p0;
    destPosition[i + 1] = p1;
    destPosition[i + 2] = p2;

    // Store the normalized cross product of p1 and p2 in p0.
    p1.sub(p0);
    p2.sub(p0);
    p1.crossInto(p2, p0).normalize();

    normals[i] = p0;
    normals[i + 1] = p0;
    normals[i + 2] = p0;

    // Copy the remaining attributes over
    for (var j = 0; j < srcAttribs.length; ++j) {
      destAttribs[j][i] = srcAttribs[j][i0];
      destAttribs[j][i + 1] = srcAttribs[j][i1];
      destAttribs[j][i + 2] = srcAttribs[j][i2];
    }
  }

  return output;
}