Gosu - change background gradient based on mouse position

gosu.rb

require 'gosu'

class FrameKeeper
  attr_reader :this, :last, :delta
  def initialize
    @last = Gosu::milliseconds
  end
  
  def update
    @this = Gosu::milliseconds
    @delta = (@this - @last) / 1000.0
    @last = @this
  end
end

class MyWindow < Gosu::Window
  WIDTH = 640
  HEIGHT = 480
  def initialize
    super(WIDTH, HEIGHT, false)
    self.caption = 'Howdy'
    @color ||= Gosu::Color.new(0xffebcd1c) # alpha, r, g, b
    @colr2 ||= Gosu::Color.new(0x33ebcd1c)
    @frames = FrameKeeper.new
  end
  
  def update
    @frames.update
    
    red = ((mouse_x % WIDTH) / WIDTH.to_f * 255).to_i << 16
    green = (@frames.this.to_i / 200 % 255) << 8
    blue = ((mouse_y % HEIGHT) / HEIGHT.to_f * 255).to_i
    color1 = 0xff000000 + red + green + blue
    color2 = 0x33000000 + red + green + blue
    @color = Gosu::Color.new(color1)
    @colr2 = Gosu::Color.new(color2)
  end
  
  def draw
    draw_quad(
      0,      0,        @color,
      WIDTH,  0,        @color,
      0,      HEIGHT,   @colr2,
      WIDTH,  HEIGHT,   @colr2,
      0
    )
  end
end

window = MyWindow.new
window.show