flash与物理引擎 创建碰撞墙

    这个星期因为工作需要快速记录学习box2d的引擎，box2d使用并不是很容易和方便，虽然资料已经很丰富，只是新的版本2.1a不能很好的兼容下面。网上很多代码有效果，但是多少调试起来 过往的案例都会出现出错。使用2.1a版本 发现已经处理了，多少和网上之前写的都不一样。

 今晚记录就是四边墙创建如下：

//创建墙   private function createWall(x:Number, y:Number, width:Number, height:Number):void  {   //演算   var bodyDef:b2BodyDef = new b2BodyDef();   bodyDef.position.Set(x / worldScale, y / worldScale);        var box:b2PolygonShape = new b2PolygonShape();   box.SetAsBox(width/2/worldScale, height/2/worldScale);   var fixtureDef:b2FixtureDef = new b2FixtureDef();   fixtureDef.shape = box;   fixtureDef.friction=0.5;//摩擦力设置   fixtureDef.restitution=0.5;//弹力设置   var body:b2Body = world.CreateBody(bodyDef);   body.CreateFixture(fixtureDef);     }

今晚发现，原来可以为墙设置摩擦力，密度，弹力。这两个特性

fixtureDef.density=10;//密度设置

fixtureDef.friction=0.5;//摩擦力设置

fixtureDef.restitution=0.5;//弹力设置

那么在拖拽物体的时候 会有一些弹性回弹的效果出现了。

而在使用的过程中 发现拖拽产生延时缓冲，所以网上一些办法是设置两个参数，而至于具体原因还有待继续去深入。

mouseJoinDef.dampingRatio = 0;

mouseJoinDef.frequencyHz = 100;

在写出这个实验的时候，多少有很多疑惑，例如设置密度有什么作用？多少范围为合理，弹力设置值范围多少算合理？

密度*体积=质量 f=ma ，那么多产生的力会不会增大？

这几天书写当中，不妨可以封装一些常见的刚体对象。如box ，circle，wall

 function drawBox(x:Number,y:Number,width:Number,height:Number,isDynamic:Boolean):void

 function drawCircle(x:Number,y:Number,radius:Number,isDynamic:Boolean):void

 function createWall(x:Number, y:Number, width:Number, height:Number):void

同样可以封装一下鼠标拖动，这些方面资料可以参考quickbox2D的作者封装的类。实现的物理效果会很容易，对于一些交互很实用。

剩下还有群组，刷选，等等还没实现。

好，只能继续探讨。

package { import flash.display.Sprite; import flash.events.*; import Box2D.Dynamics.*; import Box2D.Collision.*; import Box2D.Collision.Shapes.*; import Box2D.Common.Math.*; import Box2D.Dynamics.Joints.*; import Box2D.Dynamics.Controllers.*; public class HelloWorld extends Sprite {  //程序入口，创建一个世界  private var world:b2World = new b2World(new b2Vec2(0,10.0),true);  private var worldScale:int = 30;//30像素=1米  private  static const vesion:String="box2d for 2.1a";  private var mouseJoint:b2MouseJoint;  public function HelloWorld()  {   debugDraw();      //创建墙   createWall(10,180,20,360);   createWall(630,180,20,360);   createWall(320,10,640,20);   createWall(320,350,640,20);     for(var i:int=0;i<10;i++)   {     drawBox(Math.random()*250,100,20,20,true);//绘制矩形     drawCircle(Math.random()*100,100,20,true);//绘制圆形   }   addEventListener(Event.ENTER_FRAME, updateHandler);   stage.addEventListener(MouseEvent.MOUSE_DOWN, onMouseDownHandler);  }  //绘制一个矩形  private function drawBox(x:Number,y:Number,width:Number,height:Number,isDynamic:Boolean):void  {   var bodyDef:b2BodyDef= new b2BodyDef();   bodyDef.position.Set(x/worldScale, y/worldScale);   if (isDynamic)   {    bodyDef.type = b2Body.b2_dynamicBody;   }   var box:b2PolygonShape = new b2PolygonShape();   box.SetAsBox(width/2/worldScale, height/2/worldScale);   var fixtureDef:b2FixtureDef = new b2FixtureDef();   fixtureDef.shape = box;   var body:b2Body = world.CreateBody(bodyDef);   body.CreateFixture(fixtureDef);  }  //绘制一个圆  private function drawCircle(x:Number,y:Number,radius:Number,isDynamic:Boolean):void  {   var bodyDef:b2BodyDef= new b2BodyDef();   bodyDef.position.Set(x/worldScale, y/worldScale);   if (isDynamic)   {    bodyDef.type = b2Body.b2_dynamicBody;//设置动态类型   }      //创建圆形形状   var circle:b2CircleShape=new b2CircleShape(radius/worldScale);   var fixtureDef:b2FixtureDef = new b2FixtureDef();   fixtureDef.shape = circle;   var body:b2Body = world.CreateBody(bodyDef);   body.CreateFixture(fixtureDef);  }  //创建墙   private function createWall(x:Number, y:Number, width:Number, height:Number):void  {   //演算   var bodyDef:b2BodyDef = new b2BodyDef();   bodyDef.position.Set(x / worldScale, y / worldScale);        var box:b2PolygonShape = new b2PolygonShape();   box.SetAsBox(width/2/worldScale, height/2/worldScale);   var fixtureDef:b2FixtureDef = new b2FixtureDef();   fixtureDef.shape = box;   fixtureDef.friction=0.5;//摩擦力设置   fixtureDef.restitution=0.5;//弹力设置   var body:b2Body = world.CreateBody(bodyDef);   body.CreateFixture(fixtureDef);     }  private function debugDraw():void  {   var _debugDraw:b2DebugDraw=new b2DebugDraw();   var sprite:Sprite=new Sprite();   addChild(sprite);   _debugDraw.SetSprite(sprite);   _debugDraw.SetDrawScale(worldScale);   _debugDraw.SetFlags(b2DebugDraw.e_shapeBit);   world.SetDebugDraw(_debugDraw);  }  //交互的过程由四个步骤完成：  //第一步：获取鼠标单击处的刚体。  //第二步：创建鼠标关节。  //第三步：控制鼠标关节。  //第四步：销毁鼠标关节。  private function getBodyAtMouse(includeStatic:Boolean=false):b2Body  {   var mouseXWorldPhys:Number = (mouseX)/worldScale;   var mouseYWorldPhys:Number = (mouseY)/worldScale;   var mousePVec:b2Vec2 = new b2Vec2();   mousePVec.Set(mouseXWorldPhys, mouseYWorldPhys);   var aabb:b2AABB = new b2AABB();   aabb.lowerBound.Set(mouseXWorldPhys - 0.001, mouseYWorldPhys - 0.001);   aabb.upperBound.Set(mouseXWorldPhys + 0.001, mouseYWorldPhys + 0.001);   var body:b2Body = null;   function query(fix:b2Fixture):Boolean   {    var shape:b2Shape = b2Fixture(fix).GetShape();    if (fix.GetBody().GetType() != b2Body.b2_staticBody || includeStatic)    {     var inside:Boolean = b2Shape(shape).TestPoint(fix.GetBody().GetTransform(),mousePVec);     if (inside)     {      body = fix.GetBody();      return false;     }    }    return true;   }   world.QueryAABB(query, aabb);   return body;  }  private function onMouseDownHandler(event:MouseEvent):void  {   var mouseJoinDef:b2MouseJointDef;   var body:b2Body = this.getBodyAtMouse();   if (body)   {    mouseJoinDef = new b2MouseJointDef();    mouseJoinDef.bodyA = world.GetGroundBody();    mouseJoinDef.bodyB = body;    mouseJoinDef.target.Set((mouseX / worldScale), (mouseY / worldScale));    mouseJoinDef.maxForce = 10000;    mouseJoinDef.dampingRatio = 0;                mouseJoinDef.frequencyHz = 100;    this.mouseJoint = (world.CreateJoint(mouseJoinDef) as b2MouseJoint);   }   stage.addEventListener(MouseEvent.MOUSE_UP, onMouseUpHandler);  }  private function onMouseUpHandler(event:MouseEvent):void  {   stage.removeEventListener(MouseEvent.MOUSE_UP, onMouseUpHandler);   if (this.mouseJoint)   {    world.DestroyJoint(this.mouseJoint);//销毁鼠标关节    this.mouseJoint = null;   }  }  private function updateHandler(event:Event):void  {   world.Step(1/30,10,10);   //world.ClearForces();   world.DrawDebugData();   //拖拽部分   if (mouseJoint)   {    var mouseXWorldPhys:Number = mouseX / worldScale;    var mouseYWorldPhys:Number = mouseY / worldScale;    var p2:b2Vec2 = new b2Vec2(mouseXWorldPhys,mouseYWorldPhys);    mouseJoint.SetTarget(p2);   }  } }}