require'dxruby'

img1=Image.new(80,80,C_BLACK)

img1.circle_fill(40,40,40,C_WHITE)

x=0;dx=3

y=(Window.height-img1.height)/2

dy=3

Window.loopdo

  x+=dx;y+=dy

  if(x>Window.width-img1.width||x<0) then

    dx*=-1

  end

  if(y>Window.height-img1.height||y<0)then

    dy*=-1

  end

  Window.draw(x,y,img1)

end