module ChunkyPNG::Canvas::Adam7Interlacing

def adam7_merge_pass(pass, canvas, subcanvas)
  m_o = adam7_multiplier_offset(pass)
  0.upto(subcanvas.height - 1) do |y|
    0.upto(subcanvas.width - 1) do |x|
      new_x = x * m_o[:x_multiplier] + m_o[:x_offset]
      new_y = y * m_o[:y_multiplier] + m_o[:y_offset]
      canvas[new_x, new_y] = subcanvas[x, y]
    end
  end
  canvas
end