[Box2D]三.创建圆，长方形，凸多边形

点这看效果

下面说下凸多边形的创建．Box2D允许你创建任何种类的多边形形状，只要多边形是凸多边形，这将意味着它拥

有的所有内角要小于180度，所有的顶点要远离中心，而且你要按顺时针方向排列它们。

创建过程：

1. 首先，创建一个向量（Vector）来储存所有的顶点：

var vertices:Vector.<b2Vec2> = new Vector.<b2Vec2>();

2. 然后，我们将所有顶点作为b2Vec2对象并顺时针方向加到向量（Vector）里，

并设置b2Vec2对象的坐标(相对于刚体中心的坐标)。

vertices.push( new b2Vec2(-20/worldScale, -20/worldScale) );

vertices.push( new b2Vec2(20/worldScale, 20/worldScale) ?);

vertices.push( new b2Vec2(-20/worldScale, 20/worldScale) ?);

3. 将向（vectors）变成多边形形状

polygonShape.SetAsVector(vertices,4); ? ? //4是顶点数

package 
{	
	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.b2FixtureDef;
	import Box2D.Dynamics.b2World;
	
	import flash.display.Sprite;
	import flash.events.Event;
	import flash.events.MouseEvent;
	import flash.text.TextField;
	import flash.text.TextFieldAutoSize;
	import flash.text.TextFormat;
	
	[SWF(width="640",height="480")]
	public class Polygon extends Sprite {
		
		private var stageWidth:Number = 640;			//舞台宽度
		private var stageHeight:Number = 480;			//舞台高度
		private var backgroundColor:uint = 0x333333;	//背景色
		
		private var world:b2World;                //Box2D世界
		private var worldScale:Number = 30;        //一米等于30像素
		private var timeStep:Number = 1 / 30;    //时间步,世界将在每一个时间步被更新
		
		//只是定义了时间步还不够。在每一步，每一个物理实体（physic entity）根据作用
		//于自身的作用力来更新（不包括睡眠状态）。处理这项任务的算法叫约束解算器
		//（constraint solver）。它是基于循环每一个约束然后解算来进行的，一次一个。
		private var velIterations:int = 10;        //速率约束解算器
		private var posIterations:int = 10;        //位置约束解算器
		
		public function Polygon() {
			drawBackground();
			initWorld();
			debugDraw();
			createTip();
			createFloor();
			addEventListener(Event.ENTER_FRAME,onUpdate);
			stage.addEventListener(MouseEvent.CLICK,onStageClick);
		}
		
		private function createTip():void
		{
			var tip:TextField = new TextField();
			var format:TextFormat = new TextFormat();
			format.color = 0xFFFFFF;
			tip.autoSize = TextFieldAutoSize.LEFT;
			tip.defaultTextFormat = format;
			tip.text = "点击，随机创建圆，三角形，正方形，六边形";
			addChild(tip);
			tip.x = (stageWidth - tip.width) / 2;
		}
		
		private function initWorld():void {
			var gravity:b2Vec2 = new b2Vec2(0,9.81);    //重力
			//世界中的刚体静止时，可以允许他们进入睡眠状态,睡眠的刚体无需模拟
			var sleep:Boolean = true;
			world = new b2World(gravity,sleep);
		}
		
		private function onStageClick(event:MouseEvent):void {
			var random:Number = Math.random();
			if(random <= 0.25 ) {
				createBall(mouseX,mouseY);	
			}else if(random <= 0.5) {
				createRect(mouseX,mouseY);	
			}else if(random <= 0.75) {
				crateTriangle(mouseX,mouseY);	
			}else {
				cratePolygon(mouseX,mouseY);	
			}
		}
		
		private function createBall(x:Number,y:Number):void {
			var bodyDef:b2BodyDef = new b2BodyDef();   //刚体定义
			bodyDef.type = b2Body.b2_dynamicBody;	   //动态刚体
			//设置刚体坐标,Box2D坐标用米来表示,注册点是中心点 
			bodyDef.position.Set(x/worldScale,y/worldScale); 
			
			var circleShape:b2CircleShape = new b2CircleShape(25/worldScale); //半径为25像素的圆
			var fixtureDef:b2FixtureDef = new b2FixtureDef(); //夹具(fixture)用于将形状绑定到刚体上
			fixtureDef.density = 1;			//密度
			fixtureDef.restitution = 0.3;	//弹性系数
			fixtureDef.friction = 0.1;		//摩擦系数
			fixtureDef.shape = circleShape;
			
			var theBall:b2Body = world.CreateBody(bodyDef); //创建刚体
			theBall.CreateFixture(fixtureDef);	
		}
		
		private function createRect(x:Number,y/worldScale);
			
			var polygonShape:b2PolygonShape = new b2PolygonShape(); //创建多边形
			polygonShape.SetAsBox(20/worldScale,20/worldScale); //轴对称的矩形,半宽长和半高长
			
			var fixtureDef:b2FixtureDef = new b2FixtureDef(); //夹具(fixture)用于将形状绑定到刚体上
			fixtureDef.density = 1;			//密度
			fixtureDef.restitution = 0.1;	//弹性系数
			fixtureDef.friction = 0.1;		//摩擦系数
			fixtureDef.shape = polygonShape;
			
			var theRect:b2Body = world.CreateBody(bodyDef);
			theRect.CreateFixture(fixtureDef);	
		}
		
		private function crateTriangle(x:Number,y/worldScale); 
			
			var polygonShape:b2PolygonShape = new b2PolygonShape();
			
			var vertices:Vector.<b2Vec2> = new Vector.<b2Vec2>();
			var theX:Number = 0;
			var theY:Number = -20/worldScale;
			var angle:Number = 2 * Math.PI / 3;	//旋转角度是60度
			//这是个公式，表示点(x1,y1)绕点(0,0)旋转angle角度后的坐标(x,y)
			//x = Math.cos(angle) * x1 - Math.sin(angle) * y1;
			//y = Math.cos(angle) * y1 + Math.sin(angle) * x1;
			for (var i:int = 0; i < 3; i++) {//顺时针方向创建6个顶点
				var vec2:b2Vec2 = new b2Vec2(theX,theY);	
				vertices.push( vec2 );
				var tempX:Number = theX;
				var tempY:Number = theY;
				theX = Math.cos(angle) * tempX - Math.sin(angle) * tempY;
				theY = Math.cos(angle) * tempY + Math.sin(angle) * tempX;
			}
			polygonShape.SetAsVector(vertices,3);
			
			var fixtureDef:b2FixtureDef = new b2FixtureDef(); //夹具(fixture)用于将形状绑定到刚体上
			fixtureDef.density = 1;			//密度
			fixtureDef.restitution = 0.1;	//弹性系数
			fixtureDef.friction = 0.1;		//摩擦系数
			fixtureDef.shape = polygonShape;
			
			var polygon:b2Body = world.CreateBody(bodyDef); //创建刚体
			polygon.CreateFixture(fixtureDef);
		}
		
		private function cratePolygon(x:Number,y/worldScale); 
			
			var polygonShape:b2PolygonShape = new b2PolygonShape();
			
			var vertices:Vector.<b2Vec2> = new Vector.<b2Vec2>();
			var theX:Number = -20/worldScale;
			var theY:Number = 0;
			var angle:Number = 2 * Math.PI / 6;	//旋转角度是60度
			//这是个公式，表示点(x1,y)
			//x = Math.cos(angle) * x1 - Math.sin(angle) * y1;
			//y = Math.cos(angle) * y1 + Math.sin(angle) * x1;
			for (var i:int = 0; i < 6; i++) {//顺时针方向创建6个顶点
				var vec2:b2Vec2 = new b2Vec2(theX,6);
			
			var fixtureDef:b2FixtureDef = new b2FixtureDef(); //夹具(fixture)用于将形状绑定到刚体上
			fixtureDef.density = 1;			//密度
			fixtureDef.restitution = 0.1;	//弹性系数
			fixtureDef.friction = 0.1;		//摩擦系数
			fixtureDef.shape = polygonShape;
			
			var polygon:b2Body = world.CreateBody(bodyDef); //创建刚体
			polygon.CreateFixture(fixtureDef);
		}
	
		
		private function createFloor():void {
			var bodyDef:b2BodyDef = new b2BodyDef();   //刚体定义
			bodyDef.type = b2Body.b2_staticBody;	//静态刚体
			//设置刚体坐标,注册点是中心点 
			bodyDef.position.Set(stageWidth/2/worldScale,(stageHeight - 10)/worldScale);
			
			var polygonShape:b2PolygonShape = new b2PolygonShape(); //创建多边形
			polygonShape.SetAsBox(stageWidth/2/worldScale,10/worldScale); //轴对称的矩形,半宽长和半高长
			
			var fixtureDef:b2FixtureDef = new b2FixtureDef(); //夹具(fixture)用于将形状绑定到刚体上
			fixtureDef.density = 1;			//密度
			fixtureDef.restitution = 0.1;	//弹性系数
			fixtureDef.friction = 0.1;		//摩擦系数
			fixtureDef.shape = polygonShape;
			
			var theFloor:b2Body = world.CreateBody(bodyDef);
			theFloor.CreateFixture(fixtureDef);	
		}
		
		private function debugDraw():void {
			var debugDraw:b2DebugDraw = new b2DebugDraw(); //调试绘图类
			var debugSprite:Sprite = new Sprite(); //显示调试绘图数据的画布
			addChild(debugSprite);
			debugDraw.SetSprite(debugSprite); //告知debugSprite将要被用来显示调试绘图
			debugDraw.SetDrawScale(worldScale);
			//允许我们决定将在调试绘图（debug draw）中描绘的物
			//理实体的类型。此刻，我们只需要绘制形状
			debugDraw.SetFlags(b2DebugDraw.e_shapeBit);
			debugDraw.SetFillAlpha(0.5);
			world.SetDebugDraw(debugDraw);    
		}
		
		private function onUpdate(e:Event):void {
			world.Step(timeStep,velIterations,posIterations);
			world.ClearForces();
			world.DrawDebugData();
		}
		
		private function drawBackground():void {
			graphics.beginFill(backgroundColor);
			graphics.drawRect(0,stageWidth,stageHeight);
			graphics.endFill();
		}
		
	}
}