<?xml version="1.0" encoding="utf-8"?>
  <mx:Canvas xmlns:mx="http://www.adobe.com/2006/mxml" backgroundColor="0xFFFFFF"
          mouseDown="onMouseDown()" mouseUp="onMouseUp()">
          <mx:Script>
                  <![CDATA[
                          import mx.controls.Alert;
                          private var thickness:int = 5;
                          private var fromX:int;
                          private var fromY:int;
                          private var toX:int;
                          private var toY:int;
                          private var line:Shape = new Shape();
                          
                          private function onMouseDown():void {
                                  line.graphics.lineStyle(thickness, 0x000000);
                                  fromX = mouseX;
                                  fromY = mouseY;
                                  addEventListener(Event.ENTER_FRAME, drawLine);
                          }
                          
                          private function drawLine(e:Event):void {
                                  if(fromX != mouseX || fromY != mouseY) {
                                          line.graphics.moveTo(fromX, fromY);
                                          toX = (mouseX > this.width ? this.width : (mouseX < 0 ? 0 : mouseX));
                                          toY = (mouseY > this.height ? this.height : (mouseY < 0 ? 0: mouseY));
                                          line.graphics.lineTo(toX, toY);
                                          this.rawChildren.addChild(line);
                                          fromX = toX;
                                          fromY = toY;
                                  }
                          }
                          
                          public function onMouseUp():void {
                                  removeEventListener(Event.ENTER_FRAME, drawLine);
                          }
                          
                  ]]>
          </mx:Script>
  </mx:Canvas>