Box2d三种施加力的方法

package{
	import Box2D.Collision.Shapes.b2PolygonShape;
	import Box2D.Common.Math.b2Vec2;
	import Box2D.Dynamics.Joints.b2RevoluteJoint;
	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;
	
	[SWF(width="800",height="600",frameRate="32",backgroundColor="0x000000")]
	public class ApplicableForce extends Sprite{
		private var world:b2World;
		private var timeStep:Number;
		private var iterations:uint;
		private var pixelsPerMeter:Number = 30;
		private var frontJoint:b2RevoluteJoint;
		private var rearJoint:b2RevoluteJoint;
		
		public function ApplicableForce(){
			createWorld();
			makeDebugDraw();
			createBox(400,585,400,15,false,"ground");
			createBox(100,40,10,10,true,"left");
			createBox(400,40,10,10,true,"middle");
			createBox(700,40,10,10,true,"right");
			stage.addEventListener(MouseEvent.MOUSE_DOWN,onMouseDown);
			addEventListener(Event.ENTER_FRAME,onEnterframe);
		}
		
		private function createWorld():void{
			var gravity:b2Vec2 = new b2Vec2(0.0,9.8);
			var doSleep:Boolean = true;
			world = new b2World(gravity,doSleep);
			world.SetWarmStarting(true);
			timeStep = 1.0/30.0;
			iterations = 10;
		}
		
		private function makeDebugDraw():void{
			var debugDraw:b2DebugDraw = new b2DebugDraw();
			var debugSprite:Sprite = new Sprite();
			addChild(debugSprite);
			debugDraw.SetSprite(debugSprite);
			debugDraw.SetDrawScale(30.0);
			debugDraw.SetFillAlpha(0.5);
			debugDraw.SetLineThickness(1.0);
			debugDraw.SetFlags(b2DebugDraw.e_shapeBit);
			world.SetDebugDraw(debugDraw);
		}
		
		private function createBox(x:Number,y:Number,hx:Number,hy:Number,isDynamic:Boolean,data:String):void{
			var bodyDef:b2BodyDef = new b2BodyDef();
			bodyDef.position.Set(x/pixelsPerMeter,y/pixelsPerMeter);
			if(isDynamic){
				bodyDef.type = b2Body.b2_dynamicBody;
			}
			var box:b2PolygonShape = new b2PolygonShape();
			box.SetAsBox(hx/pixelsPerMeter,hy/pixelsPerMeter);
			var fixtureDef:b2FixtureDef = new b2FixtureDef();
			fixtureDef.shape = box;
			var body:b2Body = world.CreateBody(bodyDef);
			body.SetUserData(data);
			body.CreateFixture(fixtureDef);
		}
		
		private function onMouseDown(e:MouseEvent):void{
			var force:b2Vec2;
			for(var body:b2Body = world.GetBodyList();body;body = body.GetNext()){
				switch(body.GetUserData()){
					case "left":
						force = new b2Vec2(0,-450);
						body.ApplyForce(force,body.GetWorldCenter());
						break;
					case "middle":
						force = new b2Vec2(0,-15);
						body.ApplyImpulse(force,body.GetWorldCenter());
						break;
					case "right":
						force = new b2Vec2(0,-15);
						body.SetAwake(true);
						body.SetLinearVelocity(force);
						break;
				}
			}
		}
		
		private function onEnterframe(e:Event):void{
			world.Step(timeStep,iterations,iterations);
			world.ClearForces();
			world.DrawDebugData();
		}
	}
}