BangButton.scala

import scala.swing._

class BangIcon(ext: Int = 16) extends javax.swing.Icon {
  def getIconWidth  = ext
  def getIconHeight = ext
  
  var selected = false
  
  def paintIcon(c: java.awt.Component, g: java.awt.Graphics, x: Int, y: Int) =
    if (selected) {
      val g2 = g.asInstanceOf[java.awt.Graphics2D]
      g2.setRenderingHint(java.awt.RenderingHints.KEY_ANTIALIASING,
        java.awt.RenderingHints.VALUE_ANTIALIAS_ON)
      g2.setColor(java.awt.Color.WHITE)
//       g2.fillRoundRect(x, y, ext, ext, 4, 4)
      g2.fillOval(x, y, ext, ext)
    }
}

// val icn = new BangIcon
val r = new Button("   ") {
  var active = false
  
//   private val strkOut = new java.awt.BasicStroke(2f)
  
  private val el = new java.awt.geom.Ellipse2D.Double
  
  override def paintComponent(g2: java.awt.Graphics2D): Unit = {
    super.paintComponent(g2)
    g2.setRenderingHint(java.awt.RenderingHints.KEY_ANTIALIASING,
      java.awt.RenderingHints.VALUE_ANTIALIAS_ON)
    g2.setRenderingHint(java.awt.RenderingHints.KEY_STROKE_CONTROL,
      java.awt.RenderingHints.VALUE_STROKE_PURE)
    g2.setColor(foreground) // java.awt.Color.WHITE)
    val w = peer.getWidth
    val h = peer.getHeight
    val ext1 = math.max(0, math.min(w, h) - 14)
//     val strk = g2.getStroke
//     g2.setStroke(strkOut)
//     g2.drawOval((w - ext1) >> 1, (h - ext1) >> 1, ext1, ext1)
    el.setFrame((w - ext1) * 0.5, (h - ext1) * 0.5, ext1, ext1)
    g2.draw(el)
//     g2.setStroke(strk)
    if (active) {
      val ext2 = math.max(0, ext1 - 5)
//       g2.fillOval((w - ext2) >> 1, (h - ext2) >> 1, ext2, ext2)
      el.setFrame((w - ext2) * 0.5, (h - ext2) * 0.5, ext2, ext2)
      g2.fill(el)
    }
  }
}
//r.icon = icn
val f = new Frame {
  contents = r
  pack()
  open()
}

r.active = !r.active; r.repaint()

r.font = new java.awt.Font(java.awt.Font.SANS_SERIF, java.awt.Font.PLAIN, 30)
r.revalidate(); f.pack()

r.reactions += {
  case event.ButtonClicked(_) => 
    r.active = !r.active; r.repaint()   
}