setTile(tile, x, y) {
		this.layerData[x][y] = tile;
		this.isDirty = true;
		return tile;
	}
assign the given Tile object to the specified position
@param {Tile} tile - the tile object to be assigned
@param {number} x - x coordinate (in world/pixels coordinates)
@param {number} y - y coordinate (in world/pixels coordinates)
@returns {Tile} the tile object