淡出粒子

为了实现粒子在视觉上消失的效果，通过设置Particle的fade属性为0~1之间的小数，使它的alpha逐渐降低，从而达到淡出粒子的目的。

1package{
2    import flash.display.Sprite;
3    import flash.events.Event;
4 
5    [SWF(width="800",height="600",backgroundColor="0xffffff",frameRate="31")]
6    public class ParticleFade extends Sprite{
7        private var numbers:Number = 20;
8        private var particles:Array;
9 
10        public function ParticleFade(){
11            particles=new Array();
12            stage.addEventListener(Event.ENTER_FRAME, onEnterFrame);
13        }
14 
15        private function onEnterFrame(e:Event):void{
16            if(particles.length &lt; numbers){
17                var ball:Ball=new Ball(12, 0x00ff00, 1, 0x000000, 1);
18                addChild(ball);
19                ball.xVelocity=Math.random() * 20 - 10;
20                ball.yVelocity=Math.random() * 20 - 10;
21                ball.gravity=0.9;
22                ball.growX = 1.05;
23                ball.growY = 1.05;
24                ball.fade = 0.98;
25                ball.x=stage.stageWidth/2;
26                ball.y=stage.stageHeight/4;
27                particles.push(ball);
28            }
29            for (var i:int=0; i &lt; particles.length; i++){
30                var particle:Ball=particles[i];
31                particle.update();
32                if (particle.x - particle.radius &gt; stage.stageWidth || particle.x + particle.radius &lt; 0 || particle.y - particle.radius &gt; stage.stageHeight || particle.y + particle.radius &lt; 0){
33                    particle.xVelocity=Math.random() * 20 - 10;
34                    particle.yVelocity=Math.random() * 20 - 10;
35                    particle.x=stage.stageWidth / 2;
36                    particle.y=stage.stageHeight / 4;
37                    particle.scaleX = particle.scaleY = 1;
38                    particle.alpha = 1;
39                }
40            }
41        }
42    }
43}