def setup
  background(220)
  pink = color(255, 102, 204)
  loadPixels
  d = pixelDensity
  halfImage = 4 * (width * d) * (height / 2 * d)
  0.step(halfImage, 4) do |i|
    pixels[i + 0] = red(pink)
    pixels[i + 1] = green(pink)
    pixels[i + 2] = blue(pink)
    pixels[i + 3] = alpha(pink)
  end
  updatePixels
end