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