Arbitrarily shaped windows with Swing on OS X

ShapedWindowsOSX.scala

// arbitrary shape windows (os x)
object Test {

import javax.swing._
import java.awt._

val f = new JFrame()
f.setUndecorated(true)
f.setBackground( new Color(0,0,0,0) )
f.setSize( 400, 400 )
val cp = f.getContentPane
class Gugu extends JComponent {
   var fun = (g:Graphics2D) => ()
   override def paintComponent( g: Graphics ) {
      super.paintComponent(g)
      fun(g.asInstanceOf[Graphics2D])
   }
}
val g = new Gugu
cp.add( g, BorderLayout.CENTER )
g.fun = { g2 => g2.setColor(Color.red); g2.drawLine(0,0,g.getWidth,g.getHeight)}
// prevent the window from being dragged with the mouse
f.getRootPane.putClientProperty("apple.awt.draggableWindowBackground",java.lang.Boolean.FALSE)
f.setVisible(true)
g.fun = { g2 => g2.setColor(Color.green); g2.fillOval(0,0,g.getWidth,g.getHeight)}
g.repaint() // hmmm, the old stuff is still there
g.fun = { g2 => g2.setColor(Color.blue); g2.drawOval(0,0,g.getWidth-1,g.getHeight-1)}
cp.remove(g)
f.repaint() // hmmm, the old stuff is still there

// but this works
cp.add(g)
g.fun = { g2 => g2.clearRect(0,0,100,100)}
cp.repaint()

g.fun = { g2 => for(i<-0 to 20) { g2.clearRect(i*20,0,10,400)}}
cp.repaint()

}