render target caching

main.rb

def tick args
  args.state.background ||= {
    x: 0,
    y: Grid.h / 2,
    h: 224 * 2,
    w: 1504 * 2,
    path: "sprites/background.png"
  }

  background_sprite = args.state.background

  if !args.state.background_rt
    args.state.background_rt = args.outputs[:background]
    rt = args.state.background_rt
    rt.w = background_sprite.w
    rt.h = background_sprite.h
    rt.sprites << background_sprite.merge({x: 0, y: 0})
    args.state.background_rt_sprite = {
      x: 0,
      y: -50,
      h: 224 * 2,
      w: 1504 * 2,
      path: :background
    }
  end


  keyboard = args.inputs.keyboard

  if keyboard.right
    args.state.background.x -= 2
    args.state.background_rt_sprite.x -= 2
  elsif keyboard.left
    args.state.background.x += 2
    args.state.background_rt_sprite.x += 2
  end

  args.outputs.sprites << args.state.background
  args.outputs.sprites << args.state.background_rt_sprite
end

GTK.reset