Android Open Source - Cardboard Head Tracker

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From Project

Back to project page Cardboard.

License

The source code is released under:

Apache License

Java Source Code

package com.google.vrtoolkit.cardboard.sensors;
/*from   w ww .j  a va2  s  .  com*/
import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.opengl.Matrix;
import android.os.Handler;
import android.os.Looper;
import com.google.vrtoolkit.cardboard.sensors.internal.OrientationEKF;

public class HeadTracker {
  private static final String TAG = "HeadTracker";
  private static final double NS2S = 1.0E-9D;
  private static final int[] INPUT_SENSORS = { 1, 4 };
  private final Context mContext;
  private final float[] mEkfToHeadTracker = new float[16];
  private final float[] mTmpHeadView = new float[16];
  private final float[] mTmpRotatedEvent = new float[3];
  private Looper mSensorLooper;
  private SensorEventListener mSensorEventListener;
  private volatile boolean mTracking;
  private final OrientationEKF mTracker = new OrientationEKF();
  private long mLastGyroEventTimeNanos;

  public HeadTracker(Context context) {
    this.mContext = context;
    Matrix.setRotateEulerM(this.mEkfToHeadTracker, 0, -90.0F, 0.0F, 0.0F);
  }

  public void startTracking() {
    if (this.mTracking) {
      return;
    }
    this.mTracker.reset();

    this.mSensorEventListener = new SensorEventListener() {
      public void onSensorChanged(SensorEvent event) {
        HeadTracker.this.processSensorEvent(event);
      }

      public void onAccuracyChanged(Sensor sensor, int accuracy) {
      }
    };
    Thread sensorThread = new Thread(new Runnable() {
      public void run() {
        Looper.prepare();

        HeadTracker.this.mSensorLooper = Looper.myLooper();
        Handler handler = new Handler();

        SensorManager sensorManager = (SensorManager) HeadTracker.this.mContext
            .getSystemService("sensor");
        for (int sensorType : HeadTracker.INPUT_SENSORS) {
          Sensor sensor = sensorManager.getDefaultSensor(sensorType);
          sensorManager.registerListener(
              HeadTracker.this.mSensorEventListener, sensor, 0,
              handler);
        }
        Looper.loop();
      }
    });
    sensorThread.start();
    this.mTracking = true;
  }

  public void stopTracking() {
    if (!this.mTracking) {
      return;
    }
    SensorManager sensorManager = (SensorManager) this.mContext
        .getSystemService("sensor");

    sensorManager.unregisterListener(this.mSensorEventListener);
    this.mSensorEventListener = null;

    this.mSensorLooper.quit();
    this.mSensorLooper = null;
    this.mTracking = false;
  }

  public void getLastHeadView(float[] headView, int offset) {
    if (offset + 16 > headView.length) {
      throw new IllegalArgumentException(
          "Not enough space to write the result");
    }
    synchronized (this.mTracker) {
      double secondsSinceLastGyroEvent = (System.nanoTime() - this.mLastGyroEventTimeNanos) * 1.0E-9D;

      double secondsToPredictForward = secondsSinceLastGyroEvent + 0.03333333333333333D;
      double[] mat = this.mTracker
          .getPredictedGLMatrix(secondsToPredictForward);
      for (int i = 0; i < headView.length; i++) {
        this.mTmpHeadView[i] = ((float) mat[i]);
      }
    }
    Matrix.multiplyMM(headView, offset, this.mTmpHeadView, 0,
        this.mEkfToHeadTracker, 0);
  }

  private void processSensorEvent(SensorEvent event) {
    long timeNanos = System.nanoTime();

    this.mTmpRotatedEvent[0] = (-event.values[1]);
    this.mTmpRotatedEvent[1] = event.values[0];
    this.mTmpRotatedEvent[2] = event.values[2];
    synchronized (this.mTracker) {
      if (event.sensor.getType() == 1) {
        this.mTracker
            .processAcc(this.mTmpRotatedEvent, event.timestamp);
      } else if (event.sensor.getType() == 4) {
        this.mLastGyroEventTimeNanos = timeNanos;
        this.mTracker.processGyro(this.mTmpRotatedEvent,
            event.timestamp);
      }
    }
  }
}

Java Source Code List

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