box2d之使用b2DistanceJoint

// 代码和前面的例子一样， 只是加了四句
/*  ：
  a :  var the_joint:b2DistanceJointDef = new b2DistanceJointDef();
  b :  the_joint.Initialize(circle, box, new b2Vec2(6,2),new b2Vec2(2,2));
  c : the_joint.collideConnected = true;
  d : var joint:b2DistanceJoint = m_world.CreateJoint(the_joint)as b2DistanceJoint;

 其实Createjoint() CreateShape() CreateBody（） 的本质就是和addChild()一样  在box2d的以前的版本中 就是用的addShape()  等

*/

package {
 import flash.display.Sprite;
 import flash.events.Event;
 import Box2D.Dynamics.*;
 import Box2D.Collision.*;
 import Box2D.Collision.Shapes.*;
 import Box2D.Common.Math.*;
 import Box2D.Dynamics.Joints.*;
 import flash.events.MouseEvent;
 public class distance_joint extends Sprite {
  var mouseJoint:b2MouseJoint;
  var mousePVec:b2Vec2 = new b2Vec2();
  var bd:b2BodyDef;
  var the_circle:b2CircleDef = new b2CircleDef();
  var the_box:b2PolygonDef = new b2PolygonDef();
  var the_joint:b2DistanceJointDef = new b2DistanceJointDef();
  public function distance_joint() {
   // world setup
   var worldAABB:b2AABB = new b2AABB();
   worldAABB.lowerBound.Set(-100.0, -100.0);
   worldAABB.upperBound.Set(100.0, 100.0);
   var gravity:b2Vec2=new b2Vec2(0.0,10.0);
   var doSleep:Boolean=true;
   m_world=new b2World(worldAABB,gravity,doSleep);
   // debug draw
   var m_sprite:Sprite;
   m_sprite = new Sprite();
   addChild(m_sprite);
   var dbgDraw:b2DebugDraw = new b2DebugDraw();
   var dbgSprite:Sprite = new Sprite();
   m_sprite.addChild(dbgSprite);
   dbgDraw.m_sprite=m_sprite;
   dbgDraw.m_drawScale=30;
   dbgDraw.m_alpha = 1;
   dbgDraw.m_fillAlpha=0.5;
   dbgDraw.m_lineThickness=1;
   dbgDraw.m_drawFlags=b2DebugDraw.e_shapeBit|b2DebugDraw.e_jointBit;
   m_world.SetDebugDraw(dbgDraw);
   // ground
   the_box.SetAsBox(9,0.5);
   the_box.density = 0;
   the_box.friction = 0.4;
   the_box.restitution = 0.1;
   bd = new b2BodyDef();
   bd.position.Set(8.5, 13);
   var ground:b2Body = m_world.CreateBody(bd);
   ground.CreateShape(the_box);
   ground.SetMassFromShapes();
   // circle
   the_circle.radius = 2;
   the_circle.density = 1.0;
   the_circle.friction = 0.4;
   the_circle.restitution = 0.3;
   bd = new b2BodyDef();
   bd.position.Set(6, 2);
   var circle:b2Body = m_world.CreateBody(bd);
   circle.CreateShape(the_circle);
   circle.SetMassFromShapes();
   // square
   the_box.SetAsBox(1.5,1.5);
   the_box.density = 1.0;
   the_box.friction = 0.4;
   the_box.restitution = 0.1;
   bd = new b2BodyDef();
   bd.position.Set(2, 2);
   var box:b2Body = m_world.CreateBody(bd);
   box.CreateShape(the_box);
   box.SetMassFromShapes();
   // joint
   the_joint.Initialize(circle, box, new b2Vec2(6,2),new b2Vec2(2,2));
   //下一句是为说明连接的两个物体可以进行碰撞，设为false则为可以重叠，不能进行碰撞，即其可以相互穿过而没有阻碍
   the_joint.collideConnected = true;
   var joint:b2DistanceJoint = m_world.CreateJoint(the_joint)as b2DistanceJoint;
   // listeners
   stage.addEventListener(MouseEvent.MOUSE_DOWN, createMouse);
   stage.addEventListener(MouseEvent.MOUSE_UP, destroyMouse);
   addEventListener(Event.ENTER_FRAME, Update, false, 0, true);
  }
  public function createMouse(evt:MouseEvent):void {
   var body:b2Body=GetBodyAtMouse();
   if (body) {
    var mouseJointDef:b2MouseJointDef=new b2MouseJointDef;
    mouseJointDef.body1=m_world.GetGroundBody();
    mouseJointDef.body2=body;
    mouseJointDef.target.Set(mouseX/30, mouseY/30);
    mouseJointDef.maxForce=30000;
    mouseJointDef.timeStep=m_timeStep;
    mouseJoint=m_world.CreateJoint(mouseJointDef) as b2MouseJoint;
   }
  }
  public function destroyMouse(evt:MouseEvent):void {
   if (mouseJoint) {
    m_world.DestroyJoint(mouseJoint);
    mouseJoint=null;
   }
  }
  public function GetBodyAtMouse(includeStatic:Boolean=false):b2Body {
   var mouseXWorldPhys = (mouseX)/30;
   var mouseYWorldPhys = (mouseY)/30;
   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 k_maxCount:int=10;
   var shapes:Array = new Array();
   var count:int=m_world.Query(aabb,shapes,k_maxCount);
   var body:b2Body=null;
   for (var i:int = 0; i < count; ++i) {
    if (shapes[i].GetBody().IsStatic()==false||includeStatic) {
     var tShape:b2Shape=shapes[i] as b2Shape;
     var inside:Boolean=tShape.TestPoint(tShape.GetBody().GetXForm(),mousePVec);
     if (inside) {
      body=tShape.GetBody();
      break;
     }
    }
   }
   return body;
  }
  public function Update(e:Event):void {
   m_world.Step(m_timeStep, m_iterations);
   if (mouseJoint) {
    var mouseXWorldPhys=mouseX/30;
    var mouseYWorldPhys=mouseY/30;
    var p2:b2Vec2=new b2Vec2(mouseXWorldPhys,mouseYWorldPhys);
    mouseJoint.SetTarget(p2);
   }
  }
  public var m_world:b2World;
  public var m_iterations:int=10;
  public var m_timeStep:Number=1.0/30.0;
 }
}