Flash/Flex学习笔记(43)：3D基础

之前我们所做的动画都是基于x,y二维坐标轴的，在三维动画中我们还需要增加一个垂直于屏幕“向里”或“向外”的Z轴，那么z轴到底是应该向外，还是向里呢?这个其实无所谓，不过为了统一，习惯上通常把z轴约定为向里，即所谓的“右手坐标系”

右手坐标系的得名：伸出右手，让食指、中指、大拇指相互垂直；然后 食指指向x轴正向，中指指向y轴正向，则大拇指所指方向即为z轴正向。(事实上这个姿势酷似周杰伦周董的招牌动作)

三维透视的基本规则：

物体在Z轴上的坐标越大(越远)，则看起来越小(将上图坐标系旋转，把z轴转到x轴方向后，得到下图)，如果距离足够远，则物体将消失于屏幕上的某个特定点(通常称为“消失点”)

技术上的主要处理：动态调整物体的scaleX与scaleY（同时因为物体的大小改变后，相应的x,y坐标值通常也会改变，所以x,y坐标也要做相应调整以符合透视规则），基本公式如下：

scale = fl/(fl+z)

 
var ball:Ball = new Ball();

addChild(ball);

 

//观察点 相对于 消失点的坐标

 
var xPos:Number=0;

 
var yPos:Number=0;

 
var zPos:Number=0;

 
var fl:Number=250;//焦距

 
//消失点

 
var vpX:Number=stage.stageWidth/2;

 
var vpY:Number=stage.stageHeight/2;

 
addEventListener(Event.ENTER_FRAME, EnterFrameHandler);

 
stage.addEventListener(KeyboardEvent.KEY_DOWN, KeyDownHandler);

 
stage.addEventListener(MouseEvent.MOUSE_WHEEL,MouseWheelHandler);

 
//鼠标滚轮事件(注：必须让stage获取焦点时-即用鼠标在动画上点击一下，该事件才会触发，另外还要注意：嵌入网页时，浏览器也会响应鼠标滚轮)

 
function MouseWheelHandler(e:MouseEvent):void {

 
zPos += (e.delta*5);

 
}

 
function EnterFrameHandler(event:Event):void {

if (zPos> -fl) {

 
ball.visible=true;

 
xPos=mouseX-vpX;

yPos=mouseY-vpY;

var scale:Number = fl / (fl + zPos);

ball.scaleX=ball.scaleY=scale;

 
ball.x=vpX+xPos*scale;

 
ball.y=vpY+yPos*scale;

 
} else {

 
ball.visible=false;

 
}

 
//辅助线

graphics.clear();

 
graphics.lineStyle(1,0xcccccc);

 
graphics.moveTo(vpX,vpY);   

 
graphics.lineTo(vpX,ball.y);

 
graphics.moveTo(vpX,vpY);

graphics.lineTo(ball.x,vpY);

 

graphics.lineStyle(1,0x0000ff,0.5);

graphics.moveTo(vpX,vpY);

 
graphics.lineTo(ball.x,ball.y);

 
graphics.lineStyle(1,0xff0000,0.5);

 
graphics.moveTo(ball.x,ball.y);

 
graphics.lineTo(mouseX,mouseY); 

 
}

//键盘事件

 
function KeyDownHandler(e:KeyboardEvent):void {

if (e.keyCode==Keyboard.UP) {

 
zPos+=5;

 
} else if (e.keyCode == Keyboard.DOWN) {

 
zPos-=5;

}

 
}

这个示例中，"鼠标所在位置"充当了"观察点"(即前面示意图中的"人眼"位置)，电脑屏幕所在平面即物体的成像面，用键盘上下键可调整小球在Z轴上的位置，然后移动鼠标位置，通过辅助线观察变化。

基本的3D运动：

package {

 
import flash.display.Sprite;

 
import flash.events.Event;

 
import flash.events.KeyboardEvent;

 
import flash.ui.Keyboard;

 
import flash.display.StageAlign;

 
import flash.display.StageScaleMode;

 
public class Velocity3D extends Sprite {

 
private var ball:Ball;

 
//相当于消失点的坐标

 
private var xpos:Number=0;

private var ypos:Number=0;

private var zpos:Number=0;

//x,y,z三轴上的速度分量

 
private var vx:Number=0;

 
private var vy:Number=0;

 
private var vz:Number=0;

private var friction:Number=0.98;

 
private var fl:Number=250;

 
//消失点

private var vpX:Number=stage.stageWidth/2;

private var vpY:Number=stage.stageHeight/2;

public function Velocity3D() {

 
init();

 
}

 
private function init():void {

 
stage.align = StageAlign.TOP_LEFT;  

 
stage.scaleMode = StageScaleMode.NO_SCALE;

 
ball = new Ball(20);

addChild(ball);

addEventListener(Event.ENTER_FRAME, EnterFrameHandler);

 

stage.addEventListener(KeyboardEvent.KEY_DOWN, KeyDownHandler);

 
}

 
private function EnterFrameHandler(event:Event):void {

 
vpX =stage.stageWidth/2;

 
vpY =stage.stageHeight/2;

 
xpos+=vx;

ypos+=vy;

zpos+=vz;

 
vx*=friction;

 
vy*=friction;

 
vz*=friction;

 
if (zpos>-fl) {

 
var scale:Number = fl / (fl + zpos);

 
ball.scaleX=ball.scaleY=scale;

 
ball.x=vpX+xpos*scale;

 
ball.y=vpY+ypos*scale;

 
ball.visible=true;

 
} else {

ball.visible=false;

}

 
//辅助线

graphics.clear();

graphics.lineStyle(1,0xefefef);

graphics.moveTo(0,stage.stageHeight/2);

graphics.lineTo(stage.stageWidth,stage.stageHeight/2);

graphics.lineTo(stage.stageWidth-15,stage.stageHeight/2-8);

 
graphics.moveTo(stage.stageWidth,stage.stageHeight/2);

 
graphics.lineTo(stage.stageWidth-15,stage.stageHeight/2+8);

 
graphics.moveTo(stage.stageWidth/2,0);

 
graphics.lineTo(stage.stageWidth/2,stage.stageHeight);

 
graphics.lineTo(stage.stageWidth/2-8,stage.stageHeight-15);

 
graphics.moveTo(stage.stageWidth/2,stage.stageHeight);

 
graphics.lineTo(stage.stageWidth/2+8,stage.stageHeight-15);

graphics.lineStyle(1,0xdadada);

 
graphics.moveTo(vpX,vpY);

graphics.lineTo(ball.x,ball.y);

 
}

 
private function KeyDownHandler(e:KeyboardEvent):void {

switch (e.keyCode) {

 
case Keyboard.UP :

vy-=1;

 
break;

 
case Keyboard.DOWN :

vy+=1;

 
break;

 
case Keyboard.LEFT :

 
vx-=1;

 
break;

 
case Keyboard.RIGHT :

 
vx+=1;

break;

 
case Keyboard.SHIFT :

 
vz+=0.5;

 
break;

case Keyboard.CONTROL :

 
vz-=0.5;

 
break;

 
default :

break;

 
}

 
}

}

 
}

上下左右键控制x,y轴方向速度，shift/ctrl键控制z轴速度(当然这个示例还没考虑到3D环境中的边界反弹,下面就要谈到这个问题)

3维运动反弹：

这个需要一点想象力，二维情况下，通常只要把舞台的四个边当作边界就足够了，但是试想一下：在一个立体的空间里，要限制一个物体的活动范围，得要有6个边界面(上，下，左，右，前，后)

package {

 
import flash.display.Sprite;

import flash.events.Event;

import flash.display.StageAlign;

 
import flash.display.StageScaleMode;

public class Bounce3D extends Sprite {

 
private var ball:Ball;

 
private var xpos:Number=0;

 
private var ypos:Number=0;

 
private var zpos:Number=0;

 
private var vx:Number=Math.random()*12-6;

 
private var vy:Number=Math.random()*12-6;

 
private var vz:Number=Math.random()*12-6;

 
private var fl:Number=250;

 
//消失点

private var vpX:Number=stage.stageWidth/2;

 
private var vpY:Number=stage.stageHeight/2;

 
//相对于消失点的六个边界面(上，下，左，右，前，后)

 
private var top:Number=-100;

 
private var bottom:Number=100;

 
private var left:Number=-100;

private var right:Number=100;

 
private var front:Number=100;

 
private var back:Number=-100;

 
public function Bounce3D() {

 
init();

 
}

private function init():void {

 
stage.align = StageAlign.TOP_LEFT;  

stage.scaleMode = StageScaleMode.NO_SCALE;

 
ball=new Ball(15);

 
addChild(ball);

 
addEventListener(Event.ENTER_FRAME, EnterFrameHandler);

 
}

private function EnterFrameHandler(event:Event):void {

 
vpX =stage.stageWidth/2;

 
vpY =stage.stageHeight/2; 

xpos+=vx;

 
ypos+=vy;

 
zpos+=vz;

 
var radius:Number=ball.radius;

 
//左右边界

 
if (xpos+radius>right) {

 
xpos=right-radius;

 
vx*=-1;

 
} else if (xpos - radius < left) {

 
xpos=left+radius;

vx*=-1;

 
}

 
//上下边界

if (ypos+radius>bottom) {                

 
ypos=bottom-radius;

vy*=-1;

 
} else if (ypos - radius < top) {

 
ypos=top+radius;

 
vy*=-1;

 
}

//前后边界

if (zpos+radius>front) {

 
zpos=front-radius;

 
vz*=-1;

} else if (zpos - radius < back) {

 
zpos=back+radius;

 
vz*=-1;

}

 
//换算成平面二维坐标及缩放比率

 
if (zpos>- fl) {

var scale:Number = fl / (fl + zpos);

 
ball.scaleX=ball.scaleY=scale;

 
ball.x=vpX+xpos*scale;

 
ball.y=vpY+ypos*scale;

 
ball.visible=true;

} else {

 
ball.visible=false;

 
}

//辅助线

 
graphics.clear();

 
graphics.lineStyle(1,0xccccff);

graphics.moveTo(0,stage.stageHeight/2);

 
graphics.lineTo(stage.stageWidth,stage.stageHeight/2);

 
graphics.lineTo(stage.stageWidth-15,stage.stageHeight/2-8);

 
graphics.moveTo(stage.stageWidth,stage.stageHeight/2);

 
graphics.lineTo(stage.stageWidth-15,stage.stageHeight/2+8);

 
graphics.moveTo(0,stage.stageHeight);

 
graphics.lineTo(stage.stageWidth,0);

 
graphics.lineTo(stage.stageWidth-15,2);

 
graphics.moveTo(stage.stageWidth,0);

 
graphics.lineTo(stage.stageWidth-6,13);

 
graphics.moveTo(stage.stageWidth/2,0);

 
graphics.lineTo(stage.stageWidth/2,stage.stageHeight);

 
graphics.lineTo(stage.stageWidth/2-8,stage.stageHeight-15);

 
graphics.moveTo(stage.stageWidth/2,stage.stageHeight);

 
graphics.lineTo(stage.stageWidth/2+8,stage.stageHeight-15);

graphics.lineStyle(1,0xffccff);

 
graphics.moveTo(vpX,vpY);

 
graphics.lineTo(ball.x,ball.y);

 
}

 
}

 
}

也许这样看得并不清楚，再加入更多的小球反弹，可能更容易理解一些，不过为了方便代码处理，先定义一个新的小球类:Ball3D

 
package {

import flash.display.Sprite;

 
public class Ball3D extends Sprite {

public var radius:Number;

 
private var color:uint;

 
public var xpos:Number=0;

 
public var ypos:Number=0;

 
public var zpos:Number=0;

 
public var vx:Number=0;

 
public var vy:Number=0;

 
public var vz:Number=0;

public var mass:Number=1;

 
public function Ball3D(radius:Number=40, color:uint=0xff0000) {

this.radius=radius;

 
this.color=color;

 
init();

}

 
public function init():void {

 
graphics.lineStyle(0);

 
graphics.beginFill(color);

 
graphics.drawCircle(0, 0, radius);

 
graphics.endFill();

}

 
}

}

多个小球的3D反弹:

package {

 
import flash.display.Sprite;

 
import flash.events.Event;

import flash.display.StageAlign;

import flash.display.StageScaleMode;

 
public class MultiBounce3D extends Sprite {

 
private var balls:Array;

private var numBalls:uint=20;

 
private var fl:Number=250;

private var vpX:Number=stage.stageWidth/2;

 
private var vpY:Number=stage.stageHeight/2;

private var top:Number=-120;

 
private var bottom:Number=120;

 
private var left:Number=-120;

 
private var right:Number=120;

 
private var front:Number=120;

 
private var back:Number=-120;

 
public function MultiBounce3D() {

 
init();

}

 
private function init():void {

 
stage.align = StageAlign.TOP_LEFT;  

 
stage.scaleMode = StageScaleMode.NO_SCALE;

 
balls = new Array();

for (var i:uint = 0; i < numBalls; i++) {

 
var ball:Ball3D=new Ball3D(15,Math.random()*0xffffff);

 
balls.push(ball);

 
ball.vx=Math.random()*10-5;

ball.vy=Math.random()*10-5;

 
ball.vz=Math.random()*10-5;

 
addChild(ball);

 
}

addEventListener(Event.ENTER_FRAME, onEnterFrame);

 
}

private function onEnterFrame(event:Event):void {

 
vpX =stage.stageWidth/2;

 
vpY =stage.stageHeight/2; 

 
graphics.clear();

 
for (var i:uint = 0; i < numBalls; i++) {

 
var ball:Ball3D=balls[i];               

 
move(ball);

}

 
}

 
private function move(ball:Ball3D):void {

 
var radius:Number=ball.radius;

ball.xpos+=ball.vx;

 
ball.ypos+=ball.vy;

ball.zpos+=ball.vz;

 
//6边界检测

if (ball.xpos+radius>right) {

 
ball.xpos=right-radius;

 
ball.vx*=-1;

 
} else if (ball.xpos - radius < left) {

 
ball.xpos=left+radius;

 
ball.vx*=-1;

}

 
if (ball.ypos+radius>bottom) {

 
ball.ypos=bottom-radius;

 
ball.vy*=-1;

 
} else if (ball.ypos - radius < top) {

ball.ypos=top+radius;

 
ball.vy*=-1;

 
}

if (ball.zpos+radius>front) {

 
ball.zpos=front-radius;

 
ball.vz*=-1;

 
} else if (ball.zpos - radius < back) {

 
ball.zpos=back+radius;

 
ball.vz*=-1;

 
}

//转换化2D坐标

 
if (ball.zpos>- fl) {

 
var scale:Number = fl / (fl + ball.zpos);

 
ball.scaleX=ball.scaleY=scale;

 
ball.x=vpX+ball.xpos*scale;

 
ball.y=vpY+ball.ypos*scale;

 
ball.visible=true;

 
} else {

 
ball.visible=false;

 
}

 
//辅助线           

 
graphics.lineStyle(1,0xccccff);

graphics.moveTo(0,stage.stageHeight/2);

 
graphics.lineTo(stage.stageWidth,stage.stageHeight/2);

 
graphics.lineTo(stage.stageWidth-15,stage.stageHeight/2-8);

graphics.moveTo(stage.stageWidth,stage.stageHeight/2);

 
graphics.lineTo(stage.stageWidth-15,stage.stageHeight/2+8);

graphics.moveTo(0,stage.stageHeight);

graphics.lineTo(stage.stageWidth,0);

 
graphics.lineTo(stage.stageWidth-15,2);

 
graphics.moveTo(stage.stageWidth,0);

 
graphics.lineTo(stage.stageWidth-6,13);

graphics.moveTo(stage.stageWidth/2,0);

 
graphics.lineTo(stage.stageWidth/2,stage.stageHeight);

 
graphics.lineTo(stage.stageWidth/2-8,stage.stageHeight-15);

graphics.moveTo(stage.stageWidth/2,stage.stageHeight);

 
graphics.lineTo(stage.stageWidth/2+8,stage.stageHeight-15);

 
graphics.lineStyle(1,0xff99ff);

 
graphics.moveTo(vpX,vpY);

 

graphics.lineTo(ball.x,ball.y);

 
}

 
}

}

仔细观察一下，相信不少人会发现问题：物体的前后顺序不对，远处的物体居然挡住了近处的物体。(css中可以通过z-Index来调整，silverlight的canvas中也有类似的zIndex，但在As3中如何做呢?)

先跑一下题，来看一个小技巧：Object 数组的排序

var arrTest = [{age:20,name:"a"},{age:50,name:"b"},{age:30,name:"c"}]

 
arrTest.sortOn("age",Array.DESCENDING);//按age值倒排

 
for(var i:int=0,j=arrTest.length;i<j;i++){

 
trace(arrTest[i].age ,arrTest[i].name);

 
}

是不是很好用！

ok，问题解决了：Flash的显示列表中，最后被addChild的物体总是显示在上面，在Flash内部"舞台上的每个物体"都对应一个索引值，随着物体不断被添加到舞台上，其对应的索引值也不断增加，我们可以通过调整索引值来改变物体的显示顺序.

基本测试：

 
var ballA = new Ball(50);

 
ballA.x = stage.stageWidth/2;

 

ballA.y = stage.stageHeight/2;

addChild(ballA);

var ballB = new Ball(45,0x0000ff);

 
ballB.x = ballA.x;

 
ballB.y = ballA.y + 20;

 
addChild(ballB);

 
btn1.addEventListener(MouseEvent.MOUSE_DOWN,btn1Click);

 
function btn1Click(e:MouseEvent):void{

 
setChildIndex(ballB,0);

 
setChildIndex(ballA,1);

 
}

 
btn2.addEventListener(MouseEvent.MOUSE_DOWN,btn2Click);

 

function btn2Click(e:MouseEvent):void{

 
setChildIndex(ballB,1);

 
setChildIndex(ballA,0);

 
}

调整后的3D反弹

 
package {

 
import flash.display.Sprite;

 
import flash.events.Event;

 
import flash.display.StageAlign;

 
import flash.display.StageScaleMode;

 
public class MultiBounce3D extends Sprite {

 
private var balls:Array;

 
private var numBalls:uint=20;

private var fl:Number=250;

 
private var vpX:Number=stage.stageWidth/2;

 
private var vpY:Number=stage.stageHeight/2;

 
private var top:Number=-120;

 
private var bottom:Number=120;

 
private var left:Number=-120;

private var right:Number=120;

private var front:Number=120;

 
private var back:Number=-120;

public function MultiBounce3D() {

init();

 
}

private function init():void {

 
stage.align=StageAlign.TOP_LEFT;

 
stage.scaleMode=StageScaleMode.NO_SCALE;

 
balls = new Array();

for (var i:uint = 0; i < numBalls; i++) {

 
var ball:Ball3D=new Ball3D(15,Math.random()*0xffffff);

 
balls.push(ball);

 
ball.vx=Math.random()*10-5;

 
ball.vy=Math.random()*10-5;

 
ball.vz=Math.random()*10-5;

 
addChild(ball);

 
}

 
addEventListener(Event.ENTER_FRAME, onEnterFrame);

 
}

 
private function onEnterFrame(event:Event):void {

vpX=stage.stageWidth/2;

 
vpY=stage.stageHeight/2;

graphics.clear();

for (var i:uint = 0; i < numBalls; i++) {

 
var ball:Ball3D=balls[i];

 
move(ball);

 
}

sortZ();

}

 
function sortZ():void {

 
balls.sortOn("zpos", Array.DESCENDING | Array.NUMERIC);

 
for (var i:uint = 0; i < numBalls; i++) {

 
var ball:Ball3D=balls[i];

 
setChildIndex(ball, i);

}

}

private function move(ball:Ball3D):void {

 
var radius:Number=ball.radius;

ball.xpos+=ball.vx;

ball.ypos+=ball.vy;

 
ball.zpos+=ball.vz;

 
//6边界检测

 
if (ball.xpos+radius>right) {

 
ball.xpos=right-radius;

 
ball.vx*=-1;

 
} else if (ball.xpos - radius < left) {

 
ball.xpos=left+radius;

 
ball.vx*=-1;

}

 
if (ball.ypos+radius>bottom) {

 

ball.ypos=bottom-radius;

ball.vy*=-1;

} else if (ball.ypos - radius < top) {

ball.ypos=top+radius;

 
ball.vy*=-1;

 
}

 
if (ball.zpos+radius>front) {

 
ball.zpos=front-radius;

 
ball.vz*=-1;

 
} else if (ball.zpos - radius < back) {

 
ball.zpos=back+radius;

 
ball.vz*=-1;

 
}

//转换化2D坐标

if (ball.zpos>- fl) {

var scale:Number = fl / (fl + ball.zpos);

 
ball.scaleX=ball.scaleY=scale;

 
ball.x=vpX+ball.xpos*scale;

 
ball.y=vpY+ball.ypos*scale;

 
ball.visible=true;

 
} else {

 
ball.visible=false;

}

 
//辅助线

 
graphics.lineStyle(1,0xccccff);

 
graphics.moveTo(0,stage.stageHeight/2);

graphics.lineTo(stage.stageWidth,stage.stageHeight/2);

 
graphics.lineTo(stage.stageWidth-15,stage.stageHeight/2-8);

 
graphics.moveTo(stage.stageWidth,stage.stageHeight/2);

 
graphics.lineTo(stage.stageWidth-15,stage.stageHeight/2+8);

 
graphics.moveTo(0,stage.stageHeight);

 
graphics.lineTo(stage.stageWidth,0);

 
graphics.lineTo(stage.stageWidth-15,2);

 
graphics.moveTo(stage.stageWidth,0);

 
graphics.lineTo(stage.stageWidth-6,13);

 

graphics.moveTo(stage.stageWidth/2,0);

 
graphics.lineTo(stage.stageWidth/2,stage.stageHeight);

 
graphics.lineTo(stage.stageWidth/2-8,stage.stageHeight-15);

graphics.moveTo(stage.stageWidth/2,stage.stageHeight);

 
graphics.lineTo(stage.stageWidth/2+8,stage.stageHeight-15);

graphics.lineStyle(1,0xff99ff);

 
graphics.moveTo(vpX,vpY);

graphics.lineTo(ball.x,ball.y);

 
}

 
}

 
}

3D粒子喷射:

package {

import flash.display.Sprite;

import flash.events.Event;

import flash.display.StageAlign;

 
import flash.display.StageScaleMode;

 
//设置动画背景为黑色 

[SWF(backgroundColor=0x000000)]//c#中的特性? 哈

public class Fireworks extends Sprite {

 
private var balls:Array;

 
private var numBalls:uint=100;

 
private var fl:Number=250;

 
//消失点

 
private var vpX:Number=stage.stageWidth/2;

 
private var vpY:Number=stage.stageHeight/2;

 
private var gravity:Number=0.2;

 
private var floor:Number=50;//y轴反弹的边界(相对消失点而言)

 
private var bounce:Number=-0.6;

 
public function Fireworks() {

 
init();

 
}

 
private function init():void {

 
stage.scaleMode = StageScaleMode.NO_SCALE;

 
stage.align = StageAlign.TOP_LEFT;

 
balls = new Array();

 
for (var i:uint = 0; i < numBalls; i++) {

 
var ball:Ball3D=new Ball3D(5,Math.random()*0xffffff);

 

balls.push(ball);               

 
addChild(ball);

}

 
initVelocity();

 
addEventListener(Event.ENTER_FRAME, onEnterFrame);

 
}

 
private function initVelocity():void{

 
for (var i:uint = 0; i < numBalls; i++) {

 
var ball:Ball3D=balls[i];

 
reset(ball);

 
}           

 
}

 
private function reset(b:Ball3D):void{

 
b.ypos=-250;

 
b.zpos=200;     

 
b.xpos=0;

 
b.vx=(Math.random()*2-1)*3 //x轴方向速度为-3到+3的随机值(即:看起来有的球向左，有的球向右，在横向扩散)

 
b.vy=(Math.random()-1)*4; //y轴方向为-4到0之间的随机值(即向下掉)

 
b.vz=(Math.random()-1)*3;  //z轴方向速度为-3到0的随机值(即：所有球从远处向近处喷)

 
}

 
private function onEnterFrame(event:Event):void {           

for (var i:uint = 0; i < numBalls; i++) {

 
var ball:Ball3D=balls[i];

 
move(ball);

 
}

 
sortZ();

 
}

private function move(ball:Ball3D):void {

ball.vy+=gravity;

 
ball.xpos+=ball.vx;

 
ball.ypos+=ball.vy;

ball.zpos+=ball.vz;

 
if (ball.ypos>floor) {

 
ball.ypos=floor;

 
ball.vy*=bounce;

}

 
if (ball.zpos>-fl) {

 
var scale:Number = fl / (fl + ball.zpos);

 
ball.scaleX=ball.scaleY=scale;

 
ball.x=vpX+ball.xpos*scale;

 
ball.y=vpY+ball.ypos*scale;

 
ball.alpha = scale;//越远的物体，越淡

 
if (ball.x<0 || ball.x>stage.stageWidth || ball.y>stage.stageHeight || ball.alpha<0.05){

 
reset(ball);

 
}

 
ball.visible=true;

} else {

 
ball.visible=false;

 
reset(ball);

 
}

}

 
private function sortZ():void {

 
balls.sortOn("zpos", Array.DESCENDING | Array.NUMERIC);

 
for (var i:uint = 0; i < numBalls; i++) {

 
var ball:Ball3D=balls[i];