As3 box2d 鼠标关节

知识要点：

1，怎么获取鼠标坐标点下的刚体

2，创建鼠标关节 b2MouseJoint

3, b2World.GetGroundBody()方法

GetGroundBody

()

method

 

public function GetGroundBody():b2Body

The world provides a single static ground body with no collision shapes. You can use this to simplify the creation of joints and static shapes.

此方法提供了一个静态的地面刚体，不包含碰撞图形，可以单纯的用他来建立关节和静态的图形

private function updateMouseWorld()
        {
            _mouseX = this.mouseX;
            _mouseY = this.mouseY;
            mouseXPhy = _mouseX / PIXEL_TO_METER;
            mouseYphy = _mouseY / PIXEL_TO_METER;
        }
        
        private function getBody():b2Body
        {
            mousePVec2.Set(mouseXPhy, mouseYphy);
            //创建一个区域
            var aabb:b2AABB = new b2AABB();
            aabb.lowerBound.Set(mouseXPhy - 0.001, mouseYphy - 0.001);
            aabb.upperBound.Set(mouseXPhy - 0.001, mouseYphy - 0.001);
            var body:b2Body;
            //使用一个回调函数/查看api b2word.Queryy(,,/,,)
            function getBodyCallback(fixture:b2Fixture):Boolean
            {
                var shape:b2Shape = fixture.GetShape();
                if (fixture.GetBody().GetType() != b2Body.b2_staticBody)
                {
                    var inside:Boolean = shape.TestPoint(fixture.GetBody().GetTransform(), mousePVec2);
                    if (inside)
                    {
                        body = fixture.GetBody();
                        return false; //不进行下个fixture检查了
                    }
                }
                return true;
            }
            world.QueryAABB(getBodyCallback, aabb);
            return body;
        }
        
        private function mouseDrag()
        {
            if (bMouseDown && !mouseJoint)
            {
                var body:b2Body = getBody();
                if (body)
                {
                    trace("has a body");
                    var mouseJointDef:b2MouseJointDef = new b2MouseJointDef();
                    mouseJointDef.bodyA = world.GetGroundBody();
                    mouseJointDef.bodyB = body;
                    mouseJointDef.target.Set(mouseXPhy, mouseYphy);//设置关节的目标使用是物理世界鼠标位置
                    mouseJointDef.collideConnected = true;
                    mouseJointDef.maxForce = 100 * body.GetMass();//300*刚体质量
                    mouseJoint = world.CreateJoint(mouseJointDef) as b2MouseJoint;
                }
            }
            if (!bMouseDown)//鼠标松开销毁关节
            {
               if (mouseJoint)
               {
                   world.DestroyJoint(mouseJoint);
                   mouseJoint = null;
               }
            }
            
            if (mouseJoint)//如果有了鼠标关节 目标始终指向
            {
                mouseJoint.SetTarget(new b2Vec2(mouseXPhy,mouseYphy));
            }