               md.target.Set(mouseX, mouseY);
                  md.collideConnected = true;
                  md.maxForce = 300.0 * body.GetMass();
                  mouseJoint = world.CreateJoint(md);
                  body.SetAwake(true);
               }
            }
            
            if(mouseJoint) {
               if(isMouseDown) {
                  mouseJoint.SetTarget(new b2Vec2(mouseX, mouseY));
               } else {
                  world.DestroyJoint(mouseJoint);
                  mouse