很多时候一个多边形外观或圆形外观很难模拟复杂的事物

比如模拟一个鱼缸可能就需要拼接多个外观（b2Fixture）对象

box2d中的用法一个刚体可以绑定多个外观来进行模拟

需要注意的是跟据顶点坐标构建多边形时，都是按顺时针

package {
   import Box2D.Collision.b2WorldManifold; import Box2D.Collision.Shapes.b2CircleShape; import Box2D.Collision.Shapes.b2PolygonShape; import Box2D.Common.Math.b2Vec2; import Box2D.Dynamics.b2Body; import Box2D.Dynamics.b2BodyDef; import Box2D.Dynamics.b2DebugDraw; import Box2D.Dynamics.b2Fixture; import Box2D.Dynamics.b2FixtureDef; import Box2D.Dynamics.b2World; import comingx.Ball; import flash.display.Bitmap; import flash.display.Sprite; import flash.events.Event; import flash.system.IMEConversionMode; /**      * ...      * @author My_style */     [SWF(width="600",height="480",frameRate="30")] public class Main extends Sprite     {
           [Embed(source = "./assets/container.png")] private var ContainerImg:Class; private const PIXEL_TO_METER:int = 30; private var world:b2World; private var containerBody:b2Body; public function Main():void         {
   var c:Bitmap = new ContainerImg();             addChild(c);             c.x = stage.stageWidth / 2-c.width/2;             c.y = stage.stageHeight / 2-c.height/2;             creatWorld();             creatBall();             creatContainer(); //    creatDebugDraw();             addEventListener(Event.ENTER_FRAME, render);         } private function creatWorld():void         {
   var gravity:b2Vec2 = new b2Vec2(0, 10);             world = new b2World(gravity, true);             world.SetWarmStarting(true);//刚体初始化的时候不受重力影响         } private function creatContainer():void         {
   var coords:Array=[                                 [[61,55],[77,67],[39,135],[23,124]],                                 [[23,124],[39,135],[25,220],[6,218]],                                 [[6,218],[25,220],[44,305],[28,312]],                                 [[28,312],[44,305],[94,372],[82,384]],                                 [[82,384],[94,372],[167,413],[161,425]],                                 [[161,425],[167,413],[250,424],[250,437]],                                 [[250,438],[250,424],[339,416],[341,429]],                                 [[341,430],[339,416],[411,383],[418,393]],                                 [[418,393],[411,383],[464,327],[478,334]],                                 [[478,334],[464,327],[489,254],[504,252]],                                 [[504,252],[489,254],[488,183],[504,177]],                                 [[504,177],[488,183],[470,112],[488,103]],                                 [[488,103],[470,112],[443,66],[465,63]],                                 [[77,67],[72,46],[436,43],[443,66]]                         ]; var containerBodyDef:b2BodyDef = new b2BodyDef();             containerBodyDef.type = b2Body.b2_staticBody;             containerBodyDef.position.Set(40 / PIXEL_TO_METER, 20 / PIXEL_TO_METER);             containerBody = world.CreateBody(containerBodyDef);             creatFixtures(coords);         } private function creatFixtures(coords:Array):void         {
   for (var i:int = 0; i < coords.length; i++ ){
   var polygonShape:b2PolygonShape = new b2PolygonShape(); var shapeVertices:Array = creatVerticesArray(coords[i]);                 polygonShape.SetAsArray(shapeVertices); var fixtureDef:b2FixtureDef = new b2FixtureDef();                 fixtureDef.density = 1.0;                 fixtureDef.friction = 0.5;                 fixtureDef.restitution = 1.0;                 fixtureDef.shape = polygonShape;                 containerBody.CreateFixture(fixtureDef);             }         } private function creatVerticesArray(coords:Array):Array         {
   if (coords.length < 3)             {
   throw new Error("初始化顶点错误");             } var verticeArray:Array =  new Array(); for (var i:int = 0; i < coords.length; i++ )             {
   var vertice:b2Vec2 = new b2Vec2();                 vertice.Set(coords[i][0]/PIXEL_TO_METER, coords[i][1]/PIXEL_TO_METER);                 verticeArray.push(vertice);             } return verticeArray;         } private function creatBall():void         {
   for (var i:int = 0; i < 10; i++ ){
   var ballDef:b2BodyDef = new b2BodyDef();               ballDef.type = b2Body.b2_dynamicBody;               ballDef.position.Set(stage.stageWidth / 2 / PIXEL_TO_METER, 100 / PIXEL_TO_METER); var r:Number = Math.random() * 10 + 10; var ballShape :b2CircleShape = new b2CircleShape(r/PIXEL_TO_METER); var fixtureDef:b2FixtureDef = new b2FixtureDef();               fixtureDef.shape = ballShape;               fixtureDef.density = 1.0;               fixtureDef.friction = 0.8;               fixtureDef.restitution = 1; var ballSprite:Sprite = new Ball(r, i + "");               addChild(ballSprite);               ballDef.userData = ballSprite; var ballbody:b2Body = world.CreateBody(ballDef);               ballbody.CreateFixture(fixtureDef);             }         } private function synchorBallSprite():void         {
   var body:b2Body = world.GetBodyList(); while (body)             {
   if (body.GetDefinition().userData is Ball)                 {
   var ballSprite:Ball = body.GetDefinition().userData as Ball;                     ballSprite.x = body.GetTransform().position.x * PIXEL_TO_METER;                     ballSprite.y = body.GetTransform().position.y * PIXEL_TO_METER;                     ballSprite.rotation = body.GetTransform().GetAngle() * 180 / Math.PI;                 }                 body = body.GetNext();             }         } private function creatDebugDraw():void         {
   var debugSprite:Sprite = new Sprite();             addChild(debugSprite); var debug:b2DebugDraw = new b2DebugDraw();             debug.SetSprite(debugSprite);             debug.SetLineThickness(1);             debug.SetAlpha(1);             debug.SetFillAlpha(.8);             debug.SetFlags(b2DebugDraw.e_shapeBit | b2DebugDraw.e_jointBit);             debug.SetDrawScale(PIXEL_TO_METER);             world.SetDebugDraw(debug);         } private function render(e:Event):void         {
   var timeStep:Number = 1 / 30; var interation:int = 10;             synchorBallSprite();             world.Step(timeStep, interation, interation);             world.ClearForces(); //world.DrawDebugData();         }     } }