如何发射子弹

Question

我试图创建一个浏览器VR游戏，设置了世界，VR控制器，创建了触发事件，但是每次我扣动扳机时，之前发射的子弹就会消失。当我发射新子弹时，如何使子弹“停留”在场景中并保持移动？

我正在跟踪此示例https://threejs.org/examples/#webvr_ballshooter，但这并不是我真正需要的

        var geometry_bullet = new THREE.IcosahedronBufferGeometry( radius, 2 );
        var bullet1 = new THREE.Mesh( geometry_bullet, new THREE.MeshLambertMaterial( { color: 0x2661b9 } ) );
        bullet1.userData.velocity = new THREE.Vector3();
        bullet1.userData.velocity.x = 10;
        bullet1.userData.velocity.y = 10;
        bullet1.userData.velocity.z = 10;

        var bullet2 = new THREE.Mesh( geometry_bullet, new THREE.MeshLambertMaterial( { color: 0xee2f2f } ) );
        bullet2.userData.velocity = new THREE.Vector3();
        bullet2.userData.velocity.x = 1;
        bullet2.userData.velocity.y = 1;
        bullet2.userData.velocity.z = 1;


   ...



  function handleController( controller ) {

  if ( controller1.userData.isSelecting ) {

               bullet1.position.set(controller1.position.x   , controller1.position.y + 0.018 , controller1.position.z );
               bullet1.userData.velocity.x = 0;
               bullet1.userData.velocity.y = 10;
               bullet1.userData.velocity.z = 10;
               bullet1.userData.velocity.applyQuaternion( controller1.quaternion );


            }

 if ( controller2.userData.isSelecting ) {

                bullet2.position.set(controller2.position.x  , controller2.position.y + 0.018 , controller2.position.z );
                bullet2.userData.velocity.x = 0;
                bullet2.userData.velocity.y = 10;
                bullet2.userData.velocity.z = 10;
                 bullet2.userData.velocity.applyQuaternion( controller2.quaternion );


            }

        } ...


function render() { ... 

handleController( controller1 );
handleController( controller2 ); ...

bullet1.position.x -= bullet1.userData.velocity.x *  delta;
bullet1.position.y -= bullet1.userData.velocity.y *  delta;
bullet1.position.z -= bullet1.userData.velocity.z *  delta;
scene.add(bullet1);


bullet2.position.x -= bullet2.userData.velocity.x *  delta;
bullet2.position.y -= bullet2.userData.velocity.y *  delta;
bullet2.position.z -= bullet2.userData.velocity.z *  delta;
scene.add(bullet2);

 ...
 renderer.render( scene, camera ); 
       }