code: function(){
              var newArray = new Array2d(this.width, this.height);
              for(var x = this.width - 1; x >= 0; x--){
                  for(var y = this.height - 1; y >= 0; y--){
                      var val = this.get(x, y);
                      if(val !== void 0){
                          newArray.set(x, y, val);
                      }
                  }
              }
              return newArray;
          }
docs: Creates a copy of this Array2d. Shallow copies values.
  @method copy
  @return {Array2d}