Flash AS3 踪迹效果 拖尾效果[转]

详细代码：
/**

*Flash CS4 ActionScript 3.0

*这里呈现粒子基本技术的一个动画实例。当它到处移动时，运动的粒子在它后面

*留下了一个彗星的痕迹。这是因为粒子正在绘制到从不被抹掉的一个位图。

*滤镜应用到位图导致旧的图像慢慢地褪色离开，新的图像在顶端上绘制。

*/

package {

         import flash.display.Sprite;

         import flash.display.Bitmap;

         import flash.display.BitmapData;

         import flash.events.Event;

         import flash.geom.Point;

         import flash.filters.BlurFilter;

         import flash.geom.ColorTransform;

         import flash.display.Shape;

    

         [SWF(width = "420", height = "320", backgroundColor = "0xffffff", frameRate = "30")];

         public class Main extends Sprite {

                 private var particle:Sprite;

                 private var bitmapData:BitmapData;

                 private var bitmap:Bitmap;

                 private var velX:Number;

                 private var velY:Number;

                 private var radius:Number;

                 private var displayWidth:Number;

                 private var displayHeight:Number;

                 private var display:Sprite;

                 private var origin:Point;

                 private var blur:BlurFilter;

                 private var colorTransform1:ColorTransform;

                 private var colorTransform2:ColorTransform;

                 private var randomAccel:Number;

                 private var maxVelX:Number;

                 private var maxVelY:Number;

                 private var margin:Number;

                 public function Main():void {

                         init();

                 }

                 private function init():void {

                         radius = 5;

                         margin = radius + 2;

 

                         particle = new Sprite();

                         particle.graphics.lineStyle(2,0xffffff);

                         particle.graphics.beginFill(0xffffff,0.5);

                         particle.graphics.drawEllipse(-radius,-radius,2 * radius,2 * radius);

                         particle.graphics.endFill();

                         //设定一个开始的位置

                         particle.x = 50;

                         particle.y = 40;

                         display = new Sprite();

                         display.addChild(particle);

 

                         //运动的参数

                         velX = 1;

                         velY = 1.3;

                         randomAccel = 0.3;

                         maxVelX = 6;

                         maxVelY = 6;

 

                         //位图的大小：

                         displayWidth = 400;

                         displayHeight = 300;

 

                         //见到的位图：

                         bitmapData = new BitmapData(displayWidth,displayHeight,true,0x00000000);

                         bitmap = new Bitmap(bitmapData);

 

                         //绘制边框

                         var frame:Shape = new Shape();

                         frame.graphics.lineStyle(1,0x333333);

                         frame.graphics.drawRect(-0.5,-0.5,displayWidth + 1,displayHeight + 1);

 

                         //BlurFilter滤镜

                         blur = new BlurFilter(4,4);

                         colorTransform1 = new ColorTransform(0.999,0.95,0.9,1);

                         origin = new Point(0,0);

 

                         /*

                         这里是颜色变换改为那一个在上面。它应用透明度衰减和颜色变化。改变代                                                      码在 onEnter 结束的时候动作，以便改为使用 colorTransform 2 。

                         */

                         colorTransform2 = new ColorTransform(0.999,0.95,0.9,0.999);

 

                         bitmap.x = frame.x = 10;

                         bitmap.y = frame.y = 10;

                         this.addChild(bitmap);

                         this.addChild(frame);

 

                         this.addEventListener(Event.ENTER_FRAME, onEnter);

 

 

                 }

                 function onEnter(evt:Event):void {

        

             //随机的加速。

             velX += randomAccel*(2 * Math.random()-1);

             velY += randomAccel*(2 * Math.random()-1);

        

             //

             if (velX > maxVelX) {

                    velX = maxVelX;

              }

        

              else if (velX < -maxVelX){

                    velX = -maxVelX;

              }

               if (velY > maxVelY) {

                     velY = maxVelY;

              }

             else if (velY < -maxVelY) {

                 velY = -maxVelY;

             }

        

             // 移动粒子以及反弹粒子

            

             particle.x += velX;

             if (particle.x < margin) {

                 particle.x = margin;

                 velX *= -1;

             }

             else if (particle.x > displayWidth - margin) {

                   particle.x = displayWidth - margin;

                     velX *= -1;

             }

        

             particle.y += velY;

               if (particle.y < margin) {

                      particle.y = margin;

                      velY *= -1;

             }

             else if (particle.y > displayHeight - margin) {

                 particle.y = displayHeight - margin;

                 velY *= -1;

             }

        

             //在绘制新的图像之前应用滤镜到旧的图像。

             //粒子留下的踪迹从不抹掉，它仅仅逐渐地褪色离开。

             bitmapData.applyFilter(bitmapData,bitmapData.rect,origin,blur);

             bitmapData.colorTransform(bitmapData.rect, colorTransform1);

             bitmapData.draw(display);

        

         }

     }

}