anchor.diff:  
       return _data;
     }
  +
  +  Future<ImageDataImage> asFuture() => new Future.value(this);
   }
   
   class ImageElementImage implements TextureImage {
  
positive.code:         type = PixelType.unsignedByte;
  
    Uint8ClampedList getPixelData() => data;
  }
  
  class Uint16ListImage implements TextureImage {
  
negative.code:   int get height;
  
    bool get isReady;
  
    Future<Texture> asFuture();
  }
  
  class Texture2D implements Texture {
  