anchor.diff:    return data;
   }
   
  -Float32List FlattenVector2List(List<VM.Vector2> v, [Float32List data = null]) {
  +Float32List FlattenVector2List(List<VM.Vector2> v, [Float32List data]) {
     if (data == null) data = new Float32List(v.length * 2);
     for (int i = 0; i < v.length; ++i) {
       data[i * 2 + 0] = v[i].x;
  
positive.code:   return data;
  }
  
  Float32List FlattenVector4List(List<VM.Vector4> v, [Float32List data = null]) {
    if (data == null) data = new Float32List(v.length * 4);
    for (int i = 0; i < v.length; ++i) {
      data[i * 4 + 0] = v[i].x;
  
negative.code:   return data;
  }
  
  Float32List FlattenMatrix4List(List<VM.Matrix4> v, [Float32List data]) {
    if (data == null) data = new Float32List(v.length * 16);
    for (int i = 0; i < v.length; ++i) {
      VM.Matrix4 m = v[i];
  