[ActionScript] AS3 涂鸦的擦除和撤销功能

 package
 {
     import flash.display.Bitmap;
     import flash.display.BitmapData;
     import flash.display.BlendMode;
     import flash.display.DisplayObject;
     import flash.display.DisplayObjectContainer;
     import flash.display.Shape;
     import flash.display.Sprite;
     import flash.events.Event;
     import flash.events.MouseEvent;
     import flash.text.TextField;
     import flash.text.TextFieldAutoSize;

     [SWF(width="800",height="600")]
     public class DrawToUndo extends Sprite
     {
         private var _undoBtn:Sprite;
         private var _redoBtn:Sprite;
         private var _eraseBtn:Sprite;
         private var _drawBtn:Sprite;
         private var _canvas:Sprite;
         private var _bitmap:Bitmap;
         private var _bitmapData:BitmapData;
         private var _prevBmpd:BitmapData;
         private var _line:Shape;
         private var _thickness:Number=5;
         private var _bmpdArr:Array=[];//BitmapData数组
         private var _blendMode:String = BlendMode.NORMAL;
         private var _stepID:int=-1;
         public function DrawToUndo()
         {
             if(stage) init();
             else addEventListener(Event.ADDED_TO_STAGE,init);
         }
         private function init(e:Event=null):void
         {
             removeEventListener(Event.ADDED_TO_STAGE, init);
             _canvas = new Sprite();
             _canvas.graphics.beginFill(0,0.1);
             _canvas.graphics.drawRect(0,0,700,600);
             _canvas.graphics.endFill();
             _undoBtn = creatButton(75,25,0xeeeeee,"撤销") as Sprite;
             _redoBtn = creatButton(75,25,0xeeeeee,"重做") as Sprite;
             _eraseBtn = creatButton(75,25,0xeeeeee,"擦除") as Sprite;
             _drawBtn = creatButton(75,25,0xeeeeee,"涂鸦") as Sprite;
             _bitmap = new Bitmap();
             _bitmapData = new BitmapData(700,600,true,0);
             _bitmap.bitmapData = _bitmapData;
             _line = new Shape();

             addToDisplay(_undoBtn,this,710,10);
             addToDisplay(_redoBtn,this,710,45);
             addToDisplay(_eraseBtn,this,710,80);
             addToDisplay(_drawBtn,this,710,115);
             addToDisplay(_canvas,this);
             addToDisplay(_bitmap,_canvas);
             addToDisplay(_line,_canvas,0,0,1,false);
             initEventListener();
         }
         private function initEventListener():void
         {
             _undoBtn.addEventListener(MouseEvent.CLICK,onUndo);
             _redoBtn.addEventListener(MouseEvent.CLICK,onRedo);
             _eraseBtn.addEventListener(MouseEvent.CLICK,onErase);
             _drawBtn.addEventListener(MouseEvent.CLICK,onDraw);
             _canvas.addEventListener(MouseEvent.MOUSE_DOWN,onDown);
         }
         private function onDown(e:MouseEvent):void
         {
             stage.addEventListener(MouseEvent.MOUSE_UP,onUp);
             stage.addEventListener(MouseEvent.MOUSE_MOVE,onMove);
             _line.graphics.lineStyle(_thickness,0xff00ff);
             _line.graphics.moveTo(_canvas.mouseX,_canvas.mouseY);
             while(_stepID<_bmpdArr.length-1){
                 _bmpdArr.pop();
                 if(_stepID!=-1) _prevBmpd = _bmpdArr[_stepID];
             }
             if(_prevBmpd){
                 var bmpd:BitmapData = _prevBmpd.clone();
             }else {
                 bmpd = new BitmapData(700,600,true,0);
             }
             _stepID++;
             _bitmap.bitmapData = bmpd;
             _prevBmpd = bmpd;
             _bmpdArr.push(bmpd);

             function onMove(e:MouseEvent):void
             {
                 _line.graphics.lineTo(_canvas.mouseX,_canvas.mouseY);
                 bmpd.draw(_line,null,null,_blendMode,null,true);
             }
             function onUp(e:MouseEvent):void
             {
                 _line.graphics.clear();
                 stage.removeEventListener(MouseEvent.MOUSE_UP,onUp);
                 stage.removeEventListener(MouseEvent.MOUSE_MOVE,onMove);
             }
         }
         private function onUndo(e:MouseEvent):void
         {
             if(_stepID>0){
                 _stepID--;
                 _bitmap.bitmapData = _bmpdArr[_stepID];
                 //_prevBmpd = _bmpdArr[_stepID];
             }else{
                 _prevBmpd = null;
                 _bitmap.bitmapData = null;
                 _stepID=-1;
             }

         }
         private function onRedo(e:MouseEvent):void
         {
             if(_stepID<_bmpdArr.length-1){
                 _stepID++;
                 _bitmap.bitmapData = _bmpdArr[_stepID];
                 //_prevBmpd = _bmpdArr[_stepID];
             }
         }
         private function onErase(e:MouseEvent):void
         {
             _blendMode = BlendMode.ERASE;
             _thickness = 10;//擦除的粗细
         }
         private function onDraw(e:MouseEvent):void
         {
             _blendMode = BlendMode.NORMAL;
             _thickness = 5;//涂鸦的粗细
         }
         private function creatButton(w:Number,h:Number,color:uint,text:String=""):Sprite
         {
             var button:Sprite = new Sprite();
             button.graphics.beginFill(color,1);
             button.graphics.drawRect(0,0,w,h);
             button.graphics.endFill();
             var t:TextField = new TextField();
             t.autoSize = TextFieldAutoSize.LEFT;
             t.selectable = false;
             t.text = text;
             button.addChild(t);
             t.x = (button.width-t.width)*.5;
             t.y = (button.height-t.height)*.5;
             return button;
         }
         private function addToDisplay(target:DisplayObject,parent:DisplayObjectContainer,x:Number=0,y:Number=0,alpha:Number=1,visible:Boolean = true,scaleX:Number=1,scaleY:Number=1):void
         {
             parent.addChild(target);
             target.x = x;
             target.y = y;
             target.alpha = alpha;
             target.visible = visible;
             target.scaleX = scaleX;
             target.scaleY = scaleY;
         }
     }
 }