def each_tile_with_index level
			idx = 0
			size = tile_size level
			(0...size).each do |y|
				(0...size).each do |x|
					yield(x, y, idx) if block_given?
					idx += 1
				end
			end
		end
def each_tile_with_index level
			idx = 0
			size = tile_size level
			(0...size).each do |y|
				(0...size).each do |x|
					yield(x, y, idx) if block_given?
					idx += 1
				end
			end
		end
Builds the "x, y, index" pairs, and returns these pairs in block