Solution: Generating Geometric Masks

require 'mask'
require 'chunky_png'
class ConcentricSquaresMask < Mask
    def initialize(band_count, band_size)
      size = 2 * (band_count * 2 - 1) * band_size 
      super(size, size)
      @mid = size / 2
      @mid.times do |i|
        block = i / band_size 
        mirror_octantwise(i, block.even?)
      end
      # add a narrow bands to link the rings 
      size.times do |i|
        self[@mid, i] = true
        self[@mid - 1, i] = true
        self[i, @mid] = true
        self[i, @mid - 1] = true
      end
    end
    
    def mirror_octantwise(i, value)
      (i + 1).times do |j|
      self[@mid - j - 1, @mid - i - 1] = value 
      self[@mid - i - 1, @mid - j - 1] = value 
      self[@mid + j, @mid - i - 1] = value 
      self[@mid + i, @mid - j - 1] = value 
      self[@mid - j - 1, @mid + i] = value 
      self[@mid - i - 1, @mid + j] = value 
      self[@mid + j, @mid + i] = value
      self[@mid + i, @mid + j] = value 
      end
    end
 end