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.loop do
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