基于SceneForm实现子弹射击（绘制子弹运行轨迹）

class MainActivity : AppCompatActivity() {

 var arFragment : CleanArFragment? = null
 var camera : Camera? = null
 var size = Point(); //屏幕尺寸，控制子弹发射的初始位置
 var bullet : ModelRenderable? = null
 var scene : Scene? = null
 val SHOT = 0x1101  //绘制过程轨迹信号
 val SHOT_OVER = 0x1102 //清除子弹模型信号

 var handler = object : Handler() {
  override fun handleMessage(msg : Message)
  {
   if (msg.what == SHOT) { //绘制移动过程中的轨迹
    var currentStatus = msg.obj as CurrentStatus
    currentStatus.node.worldPosition = currentStatus.status
   } else if (msg.what == SHOT_OVER) { //一次射击完成，清除屏幕的子弹
    var node = msg.obj as Node
    scene!!.removeChild(node)
   }
  }
 }

 override fun onCreate(savedInstanceState: Bundle?) {
  super.onCreate(savedInstanceState)
  setContentView(R.layout.activity_main)

  // 获取屏幕尺寸
  val display = windowManager.defaultDisplay
  display.getRealSize(size)
  arFragment = this.supportFragmentManager.findFragmentById(R.id.arFragment) as CleanArFragment
  arFragment!!.arSceneView.planeRenderer.isEnabled = false  //禁止 sceneform 框架的平面绘制
  scene = arFragment!!.arSceneView.scene
  camera = scene!!.camera

  initbullet()
  shootButton.setOnClickListener(listener)
 }

 var listener : View.OnClickListener = object : View.OnClickListener{
  override fun onClick(v: View?) {
   shoot()
  }
 }

 @TargetApi(Build.VERSION_CODES.N)
 //初始化子弹模型
 private fun initbullet() {
  Texture.builder().setSource(this@MainActivity, R.drawable.texture).build()
   .thenAccept(
    { texture ->
    MaterialFactory.makeOpaqueWithTexture(this@MainActivity, texture)
     .thenAccept { material ->
      // 设置子弹模型为球体
      bullet = ShapeFactory.makeSphere(0.1f, Vector3(0f, 0f, 0f), material) }
    }
   )
 }

 private fun shoot() {
  //从屏幕发出的射线，对应子弹的运行轨迹
  var ray = camera!!.screenPointToRay(size.x / 2f, size.y / 2f);
  var node = Node() //子弹节点
  node.renderable = bullet //子弹节点加载子弹模型
  scene!!.addChild(node)

  Thread(object : Runnable{
   override fun run() {

    //子弹射击过程中的轨迹，子线程处理轨迹事件，主线程改变轨迹位置
    for (i in 1 .. 200 ) { //子弹射程 20 m
     var stepLen = i;
     var currentPoint = ray.getPoint(stepLen * 0.1f)
     var msg = handler.obtainMessage()
     msg.what = SHOT
     msg.obj = CurrentStatus(node, currentPoint)
     handler.sendMessage(msg)
    }

    //子弹超出距离后，从屏幕清除掉
    var msg = handler.obtainMessage()
    msg.what = SHOT_OVER
    msg.obj = node
    handler.sendMessage(msg)
   }
  }).start()
 }

 // 子线程和主线程穿点的数据类
 data class CurrentStatus(var node : Node, var status : Vector3)
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  tools:context=".MainActivity">

 <fragment
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:id="@+id/arFragment"
   android:name="com.hosh.shootapplication.CleanArFragment"/>


 <View
   android:layout_width="35dp"
   android:layout_height="2dp"
   android:background="#ff0000"
   android:layout_centerInParent="true" />

 <View
   android:layout_width="2dp"
   android:layout_height="35dp"
   android:background="#ff0000"
   android:layout_centerInParent="true" />

 <Button
   android:layout_width="wrap_content"
   android:layout_height="wrap_content"
   android:id="@+id/shootButton"
   android:layout_alignParentBottom="true"
   android:layout_centerHorizontal="true"
   android:layout_marginBottom="8dp"
   android:text="@string/shoot"
 />

</RelativeLayout>