[Android] AR Engine运动跟踪能力，高精度实现沉浸式AR体验

• 实现6DOF的运动跟踪方式（世界跟踪方式），能从不同距离、方向、角度观察虚拟物体，营造更加真实的AR体验环境；
  
• 实现单目ATE（绝对轨迹误差）低至1.6cm，确保虚拟物体稳定性，体验效果更佳。
  
• 平面检测时长小于1秒，平面识别和扩展速度更快。
  

• 打开Android Studio项目级“build.gradle”文件。添加Maven代码库。（这里以7.0以下版本举例）
  在“buildscript > repositories”中配置HMS Core SDK的Maven仓地址。
  在“allprojects > repositories”中配置HMS Core SDK的Maven仓地址。
  

buildscript {
  repositories {
    google()
    jcenter()
    // 配置HMS Core SDK的Maven仓地址。
    maven {url "https://developer.huawei.com/repo/" }
  }
}
allprojects {
  repositories {
    google()
    jcenter()
    // 配置HMS Core SDK的Maven仓地址。
    maven {url "https://developer.huawei.com/repo/" }
  }
}

• 打开项目中应用级的“build.gradle”文件。
  

dependencies {
implementation 'com.huawei.hms:arenginesdk:3.1.0.1'
}

• 检查当前设备是否安装了AR Engine，若已经安装则正常运行，若没有安装主动跳转应用市场，请求安装AR Engine。
  

private boolean arEngineAbilityCheck() {
  boolean isInstallArEngineApk = AREnginesApk.isAREngineApkReady(this);
  if (!isInstallArEngineApk && isRemindInstall) {
    Toast.makeText(this, "Please agree to install.", Toast.LENGTH_LONG).show();
    finish();
  }
  LogUtil.debug(TAG, "Is Install AR Engine Apk: " + isInstallArEngineApk);
  if (!isInstallArEngineApk) {
    startActivity(new Intent(this, com.huawei.arengine.demos.common.ConnectAppMarketActivity.class));
    isRemindInstall = true;
  }
  return AREnginesApk.isAREngineApkReady(this);
}

• 运行前权限检查
  

AndroidManifest里面配置相机权限
<uses-permission android:name="android.permission.CAMERA" />
private static final int REQUEST_CODE_ASK_PERMISSIONS = 1;
private static final int MAX_ARRAYS = 10;
private static final String[] PERMISSIONS_ARRAYS = new String[]{Manifest.permission.CAMERA};
List<String> permissionsList = new ArrayList<>(MAX_ARRAYS);
boolean isHasPermission = true;
for (String permission : PERMISSIONS_ARRAYS) {
  if (ContextCompat.checkSelfPermission(activity, permission) != PackageManager.PERMISSION_GRANTED) {
    isHasPermission = false;
    break;
  }
}
if (!isHasPermission) {
  for (String permission : PERMISSIONS_ARRAYS) {
    if (ContextCompat.checkSelfPermission(activity, permission) != PackageManager.PERMISSION_GRANTED) {
      permissionsList.add(permission);
    }
  }
  ActivityCompat.requestPermissions(activity,
    permissionsList.toArray(new String[permissionsList.size()]), REQUEST_CODE_ASK_PERMISSIONS);
}

• 调用ARWorldTrackingConfig接口，创建运动跟踪ARSession，
  

private ARSession mArSession;
private ARWorldTrackingConfig mConfig;
config.setCameraLensFacing(ARConfigBase.CameraLensFacing.FRONT);   // 通过config.setXXX方法配置场景参数
config.setPowerMode(ARConfigBase.PowerMode.ULTRA_POWER_SAVING);
mArSession.configure(config);
mArSession.resume();
mArSession.configure(config);

mSession.setCameraTextureName(mTextureDisplay.getExternalTextureId());
ARFrame arFrame = mSession.update();  // 从ARSession中获取一帧的数据。
// Set the environment texture probe and mode after the camera is initialized.
setEnvTextureData();
ARCamera arCamera = arFrame.getCamera();  // 可以从ARFrame中获取ARCamera，ARCamera对象可以获取相机的投影矩阵，用来渲染窗口。
// The size of the projection matrix is 4 * 4.
float[] projectionMatrix = new float[16];
arCamera.getProjectionMatrix(projectionMatrix, PROJ_MATRIX_OFFSET, PROJ_MATRIX_NEAR, PROJ_MATRIX_FAR);
mTextureDisplay.onDrawFrame(arFrame);
StringBuilder sb = new StringBuilder();
updateMessageData(arFrame, sb);
mTextDisplay.onDrawFrame(sb);
// The size of ViewMatrix is 4 * 4.
float[] viewMatrix = new float[16];
arCamera.getViewMatrix(viewMatrix, 0);
for (ARPlane plane : mSession.getAllTrackables(ARPlane.class)) {  // 从ARSession中获取所有的可跟踪平面。
  if (plane.getType() != ARPlane.PlaneType.UNKNOWN_FACING
    && plane.getTrackingState() == ARTrackable.TrackingState.TRACKING) {
    hideLoadingMessage();
    break;
  }
}
drawTarget(mSession.getAllTrackables(ARTarget.class), arCamera, viewMatrix, projectionMatrix);
mLabelDisplay.onDrawFrame(mSession.getAllTrackables(ARPlane.class), arCamera.getDisplayOrientedPose(),
  projectionMatrix);
handleGestureEvent(arFrame, arCamera, projectionMatrix, viewMatrix);
ARLightEstimate lightEstimate = arFrame.getLightEstimate();
ARPointCloud arPointCloud = arFrame.acquirePointCloud();
getEnvironmentTexture(lightEstimate);
drawAllObjects(projectionMatrix, viewMatrix,  getPixelIntensity(lightEstimate));
mPointCloud.onDrawFrame(arPointCloud, viewMatrix, projectionMatrix);
ARHitResult hitResult = hitTest4Result(arFrame, arCamera, event.getEventSecond());
if (hitResult != null) {
  mSelectedObj.setAnchor(hitResult.createAnchor());  // 在命中检测位置创建锚点，使得AREngine持续跟踪。
}

• 根据锚点位置来绘制所需的虚拟物体。
  

mEnvTextureBtn.setOnCheckedChangeListener((compoundButton, b) -> {
  mEnvTextureBtn.setEnabled(false);
  handler.sendEmptyMessageDelayed(MSG_ENV_TEXTURE_BUTTON_CLICK_ENABLE,
      BUTTON_REPEAT_CLICK_INTERVAL_TIME);
  mEnvTextureModeOpen = !mEnvTextureModeOpen;
  if (mEnvTextureModeOpen) {
     mEnvTextureLayout.setVisibility(View.VISIBLE);
  } else {
    mEnvTextureLayout.setVisibility(View.GONE);
  }
  int lightingMode = refreshLightMode(mEnvTextureModeOpen, ARConfigBase.LIGHT_MODE_ENVIRONMENT_TEXTURE);
  refreshConfig(lightingMode);
});