content: /*
   * Copyright 2017 Google Inc. All Rights Reserved.
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package com.google.ar.core.examples.java.helloar;
  
  import android.app.Activity;
  import android.content.Context;
  import android.hardware.display.DisplayManager;
  import android.hardware.display.DisplayManager.DisplayListener;
  import android.view.Display;
  import android.view.WindowManager;
  
  import com.google.ar.core.Session;
  
  /**
   * Helper to track the display rotations. In particular, the 180 degree rotations are not notified
   * by the onSurfaceChanged() callback, and thus they require listening to the android display
   * events.
   */
  public class DisplayRotationHelper implements DisplayListener {
      private boolean viewportChanged;
      private int viewportWidth;
      private int viewportHeight;
      private final Context context;
      private final Display display;
  
      /**
       * Constructs the DisplayRotationHelper but does not register the listener yet.
       *
       * @param context the Android {@link Context}.
       */
      public DisplayRotationHelper(Context context) {
          this.context = context;
          display = context.getSystemService(WindowManager.class).getDefaultDisplay();
      }
  
      /** Registers the display listener. Should be called from {@link Activity#onResume()}. */
      public void onResume() {
          context.getSystemService(DisplayManager.class).registerDisplayListener(this, null);
      }
  
      /** Unregisters the display listener. Should be called from {@link Activity#onPause()}. */
      public void onPause() {
          context.getSystemService(DisplayManager.class).unregisterDisplayListener(this);
      }
  
      /**
       * Records a change in surface dimensions. This will be later used by {@link
       * #updateSessionIfNeeded(Session)}. Should be called from {@link
       * android.opengl.GLSurfaceView.Renderer
       * #onSurfaceChanged(javax.microedition.khronos.opengles.GL10, int, int)}.
       *
       * @param width the updated width of the surface.
       * @param height the updated height of the surface.
       */
      public void onSurfaceChanged(int width, int height) {
          viewportWidth = width;
          viewportHeight = height;
          viewportChanged = true;
      }
  
      /**
       * Updates the session display geometry if a change was posted either by {@link
       * #onSurfaceChanged(int, int)} call or by {@link #onDisplayChanged(int)} system callback. This
       * function should be called explicitly before each call to {@link Session#update()}. This
       * function will also clear the 'pending update' (viewportChanged) flag.
       *
       * @param session the {@link Session} object to update if display geometry changed.
       */
      public void updateSessionIfNeeded(Session session) {
          if (viewportChanged) {
              int displayRotation = display.getRotation();
              session.setDisplayGeometry(displayRotation, viewportWidth, viewportHeight);
              viewportChanged = false;
          }
      }
  
      /**
       * Returns the current rotation state of android display. Same as {@link Display#getRotation()}.
       */
      public int getRotation() {
          return display.getRotation();
      }
  
      @Override
      public void onDisplayAdded(int displayId) {}
  
      @Override
      public void onDisplayRemoved(int displayId) {}
  
      @Override
      public void onDisplayChanged(int displayId) {
          viewportChanged = true;
      }
  }
  