module ChunkyPNG::Canvas::Operations

def compose(new_foreground, dx = 0, dy = 0)
  check_size_constraints!(new_foreground, dx, dy)
  for y in 0...new_foreground.height do
    for x in 0...new_foreground.width do
      self[x+dx, y+dy] = ChunkyPNG::Color.compose(new_foreground[x, y], self[x+dx, y+dy])
    end
  end
  self
end