Android용 인스턴트 게재위치 개발자 가이드

앱에서 Instant Placement API를 사용하는 방법을 알아봅니다.

기본 요건

계속 진행하기 전에 기본 AR 개념과 ARCore 세션 구성 방법을 이해해야 합니다.

인스턴트 게재위치를 사용하여 새 세션 구성

새 ARCore 세션에서 인스턴트 게재위치 모드를 사용 설정합니다.

Java

// Create the ARCore session.
public void createSession() {
  session = new Session(applicationContext);
  Config config = new Config(session);
  // Set the Instant Placement mode.
  config.setInstantPlacementMode(InstantPlacementMode.LOCAL_Y_UP);
  session.configure(config);
}

Kotlin

// Create the ARCore session.
fun createSession() {
  session = Session(applicationContext);
  val config = Config(session)
  // Set the Instant Placement mode.
  config.instantPlacementMode = Config.InstantPlacementMode.LOCAL_Y_UP
  session.configure(config)
}

객체 배치

Frame.hitTestInstantPlacement()를 사용하여 화면 탭 위치가 지정된 추적 가능한 인스턴트 게재위치 포인트를 만듭니다. getPose() 메서드로 현재 포즈를 가져옵니다.

Java

private placementIsDone = false;

public void onDrawFrame(GL10 gl) {
  Frame frame = session.update();

  // Place an object on tap.
  if (!placementIsDone && didUserTap()) {
    // Use estimated distance from the user's device to the real world, based
    // on expected user interaction and behavior.
    float approximateDistanceMeters = 2.0f;
    // Performs a ray cast given a screen tap position.
    List<HitResult> results =
      frame.hitTestInstantPlacement(tapX, tapY, approximateDistanceMeters);
    if (!results.isEmpty()) {
      InstantPlacementPoint point = (InstantPlacementPoint) results.get(0).getTrackable();
      // Create an Anchor from the point's pose.
      Anchor anchor = point.createAnchor(point.getPose());
      placementIsDone = true;
      disableInstantPlacement();
    }
  }
}

Kotlin

var placementIsDone = false;

fun onDrawFrame(gl: GL10) {
  val frame = session.update();

  // Place an object on tap.
  if (!placementIsDone && didUserTap()) {
    // Use estimated distance from the user's device to the real world, based
    // on expected user interaction and behavior.
    val approximateDistanceMeters = 2.0f;
    // Performs a ray cast given a screen tap position.
    val results = frame.hitTestInstantPlacement(tapX, tapY, approximateDistanceMeters)
    if (results.isNotEmpty()) {
      val point = results[0].trackable as InstantPlacementPoint
      // Create an Anchor from the point's pose.
      val anchor = point.createAnchor(point.pose)
      placementIsDone = true
      disableInstantPlacement()
    }
  }
}

인스턴트 게재위치는 대략적인 거리로 화면 공간 추적을 지원하며 인스턴트 게재위치 포인트가 실제 세계에 고정되면 자동으로 전체 추적으로 전환됩니다. getPose()를 사용하여 현재 포즈를 가져옵니다. getTrackingMethod()를 사용하여 현재 추적 메서드를 가져옵니다.

ARCore는 모든 방향의 표면에서 인스턴트 게재위치 히트 테스트를 실행할 수 있지만 히트 결과에서는 항상 중력 방향을 기준으로 +Y가 위로 향하는 포즈를 반환합니다. 가로 표면에서는 히트 테스트가 정확한 위치를 훨씬 더 빠르게 반환합니다.

원활한 추적 방법 전환

실제 깊이를 사용할 수 있게 되면 ARCore는 InstantPlacementPoint의 추적 메서드를 SCREENSPACE_WITH_APPROXIMATE_DISTANCE에서 FULL_TRACKING로 변경합니다. 점의 포즈도 실제 깊이를 반영하도록 변경됩니다. 이로 인해 객체가 갑자기 커지거나 축소되는 것처럼 보일 수 있습니다. 이 갑작스러운 변경을 방지하려면 InstantPlacementPoint 래퍼를 추가합니다.

Java

// Wrapper class to track state to reduce sudden visual changes in object size
class WrappedInstantPlacement {
  public InstantPlacementPoint point;
  public InstantPlacementPoint.TrackingMethod previousTrackingMethod;
  public float previousDistanceToCamera;
  public float scaleFactor = 1.0f;

  public WrappedInstantPlacement(
      InstantPlacementPoint point,
      InstantPlacementPoint.TrackingMethod previousTrackingMethod,
      float previousDistanceToCamera) {
    this.point = point;
    this.previousTrackingMethod = previousTrackingMethod;
    this.previousDistanceToCamera = previousDistanceToCamera;
  }
}

Kotlin

// Wrapper class to track state to reduce sudden visual changes in object size
class WrappedInstantPlacement(
  var point: InstantPlacementPoint,
  var previousTrackingMethod: InstantPlacementPoint.TrackingMethod,
  var previousDistanceToCamera: Float,
  var scaleFactor: Float = 1.0f
)

그런 다음 활동에 다음을 추가합니다.

Java

List<WrappedInstantPlacement> wrappedPoints = new ArrayList<>();

public void onDrawFrame(GL10 gl) {
  Frame frame = session.update();
  Camera camera = frame.getCamera();

  // Place an object on tap.
  if (didUserTap()) {
    // Instant Placement should only be applied if no results are available through hitTest.
    List<HitResult> results = frame.hitTest(tapX, tapY);
    if (results.isEmpty()) {
      // Use the estimated distance from the user's device to the closest
      // available surface, based on expected user interaction and behavior.
      float approximateDistanceMeters = 2.0f;

      // Returns a single result if the hit test was successful.
      results =
          frame.hitTestInstantPlacement(tapX, tapY, approximateDistanceMeters);
      if (!results.isEmpty()) {
        // Instant placement was successful.
        InstantPlacementPoint point = (InstantPlacementPoint) results.get(0).getTrackable();
        wrappedPoints.add(new WrappedInstantPlacement(point, point.getTrackingMethod(),
          distance(camera.getPose(), point.getPose())));
      }
    } else {
      // results contain valid hit tests which can be used directly, so instant placement is not required.
    }
  }

  for (WrappedInstantPlacement wrappedPoint : wrappedPoints) {
    InstantPlacementPoint point = wrappedPoint.point;
    if (point.getTrackingState() == TrackingState.STOPPED) {
      wrappedPoints.remove(wrappedPoint);
      continue;
    }
    if (point.getTrackingState() == TrackingState.PAUSED) {
      continue;
    }

    if (point.getTrackingMethod() == TrackingMethod.SCREENSPACE_WITH_APPROXIMATE_DISTANCE) {
       // Continue to use the estimated depth and pose. Record the distance to
       // the camera for use in the next frame if the transition to full
       // tracking happens.
       wrappedPoint.previousDistanceToCamera = distance(point.getPose(), camera.getPose());
    }
    else if (point.getTrackingMethod() == TrackingMethod.FULL_TRACKING) {
      if (wrappedPoint.previousTrackingMethod == TrackingMethod.SCREENSPACE_WITH_APPROXIMATE_DISTANCE) {
        // Change from the estimated pose to the accurate pose. Adjust the
        // object scale to counteract the apparent change due to pose jump.
        wrappedPoint.scaleFactor = distance(point.getPose(), camera.getPose()) /
            wrappedPoint.previousDistanceToCamera;
        // Apply the scale factor to the model.
        // ...
        wrappedPoint.previousTrackingMethod = TrackingMethod.FULL_TRACKING;
      }
    }
  }
}

float distance(Pose p, Pose q) {
  return Math.sqrt(Math.pow(p.tx() - q.tx(), 2) + Math.pow(p.ty() - q.ty(), 2) + Math.pow(p.tz() - q.tz(), 2));
}

Kotlin

var wrappedPoints = mutableListOf<WrappedInstantPlacement>()

fun onDrawFrame(gl: GL10?) {
  val frame = session.update()
  val camera = frame.camera

  // Place an object on tap.
  if (didUserTap()) {
    // Instant Placement should only be applied if no results are available through hitTest.
    var results = frame.hitTest(tapX, tapY);
    if (results.isEmpty()) {
      // Use the estimated distance from the user's device to the closest
      // available surface, based on expected user interaction and behavior.
      val approximateDistanceMeters = 2.0f;

      // Returns a single result if the hit test was successful.
      results = frame.hitTestInstantPlacement(tapX, tapY, approximateDistanceMeters);
      if (results.isNotEmpty()) {
        // Instant placement was successful.
        val point = results[0].trackable as InstantPlacementPoint
        val wrapped = WrappedInstantPlacement(point, point.trackingMethod, point.pose.distance(camera.pose))
        wrappedPoints.add(wrapped)
      }
    } else {
      // Results contain valid hit tests which can be used directly, so Instant Placement 
      // is not required.
    }
  }

  loop@ for (wrappedPoint in wrappedPoints) {
    val point = wrappedPoint.point
    when {
      point.trackingState == TrackingState.STOPPED -> {
        wrappedPoints.remove(wrappedPoint)
        continue@loop
      }
      point.trackingState == TrackingState.PAUSED -> continue@loop
      point.trackingMethod == TrackingMethod.SCREENSPACE_WITH_APPROXIMATE_DISTANCE -> {
        // Continue to use the estimated depth and pose. Record the distance to
        // the camera for use in the next frame if the transition to full
        // tracking happens.
        wrappedPoint.previousDistanceToCamera = point.pose.distance(camera.pose)
      }
      wrappedPoint.previousTrackingMethod == TrackingMethod.SCREENSPACE_WITH_APPROXIMATE_DISTANCE &&
      point.trackingMethod == TrackingMethod.FULL_TRACKING -> {
        // Change from the estimated pose to the accurate pose. Adjust the
        // object scale to counteract the apparent change due to pose jump.
        wrappedPoint.scaleFactor =
          point.pose.distance(camera.pose) / wrappedPoint.previousDistanceToCamera
        // Apply the scale factor to the model.
        // ...
        wrappedPoint.previousTrackingMethod = TrackingMethod.FULL_TRACKING
      }
    }
  }
}

fun Pose.distance(other: Pose) = sqrt(
  (tx() - other.tx()).pow(2.0f) + (ty() - other.ty()).pow(2.0f) + (tz() - other.tz()).pow(2.0f)
)

객체 배치 후 효율성 향상

CPU 주기 및 전원을 절약하기 위해 객체가 올바르게 배치된 경우 인스턴트 게재위치를 사용 중지합니다.

Java

void disableInstantPlacement() {
  Config config = new Config(session);
  config.setInstantPlacementMode(Config.InstantPlacementMode.DISABLED);
  session.configure(config);
}

Kotlin

fun disableInstantPlacement() {
  val config = Config(session)
  // Set the Instant Placement mode.
  config.instantPlacementMode = Config.InstantPlacementMode.DISABLED
  session.configure(config)
}