box2d joint应用

    用了两种关节，距离关节和鼠标关节，距离关节是用约束两个刚体的，算是最简单的一种，初始化很简单：

			var disj:b2DistanceJointDef =new  b2DistanceJointDef();
			disj.Initialize(poly, poly2, new b2Vec2(15, 3), new b2Vec2(17, 9));
			var dis:b2DistanceJoint = world.CreateJoint(disj ) as b2DistanceJoint;

鼠标关节用来拖动刚体。

private function mousedrag():void 
        {
            if (mousedown&&!mouseJoint)
            {
                var bodyy:b2Body = getBodyAtMouse();
                if (bodyy)
                {
                    var md:b2MouseJointDef = new b2MouseJointDef();
                    md.bodyA = world .GetGroundBody();
                    md.bodyB = bodyy;
                    
                    md.target.Set(mousepx ,mousepy);
                    md.collideConnected = true;
                    md.maxForce = 1000.0 * bodyy.GetMass();
                    mouseJoint = world.CreateJoint(md) as b2MouseJoint;
                    bodyy.SetAwake(true);
                }
            }
            if (!mousedown)
            {
                if (mouseJoint)
                {
                    world .DestroyJoint(mouseJoint );
                    mouseJoint = null;
                }
            }
            if (mouseJoint)
            {
                mouseJoint.SetTarget(new b2Vec2(mousepx, mousepy));
                
            }
        }

getBodyAtMouse()用来查找位于鼠标下的刚体，

private function getBodyAtMouse(includeStatic:Boolean = false):b2Body
        {
            //创建一个小的边界区域
            _mousePVec.Set(mousepx ,mousepy);
            var aabb:b2AABB = new b2AABB();
            aabb.lowerBound.Set(mousepx  - 0.001,mousepy - 0.001);
            aabb.upperBound.Set(mousepx  + 0.001,mousepy + 0.001);
            var bodyyy:b2Body = null;
            var fixture:b2Fixture;
            
            //回调函数的形式获取鼠标下面的刚体
            function getBodyCallback(fixture:b2Fixture):Boolean
            {
                var shape:b2Shape = fixture.GetShape();
                if(fixture.GetBody().GetType() != b2Body.b2_staticBody || includeStatic)
                {
                    var inside:Boolean = shape.TestPoint(fixture.GetBody().GetTransform(),_mousePVec);
                    if(inside)
                    {
                        bodyyy= fixture.GetBody();
                        return false;
                    }
                }
                return true;
            }
            world.QueryAABB(getBodyCallback, aabb);
            return bodyyy;
        }

box2d 2.1 源代码