feat: 切换后端至PaddleOCR-NCNN，切换工程为CMake

1.项目后端整体迁移至PaddleOCR-NCNN算法，已通过基本的兼容性测试
2.工程改为使用CMake组织，后续为了更好地兼容第三方库，不再提供QMake工程
3.重整权利声明文件，重整代码工程，确保最小化侵权风险

Log: 切换后端至PaddleOCR-NCNN，切换工程为CMake
Change-Id: I4d5d2c5d37505a4a24b389b1a4c5d12f17bfa38c

3rdparty/opencv-4.5.4/samples/android/face-detection/CMakeLists.txt

@@ -0,0 +1,12 @@
+set(sample example-face-detection)
+
+if(BUILD_FAT_JAVA_LIB)
+  set(native_deps opencv_java)
+else()
+  set(native_deps opencv_objdetect)
+endif()
+
+add_android_project(${sample} "${CMAKE_CURRENT_SOURCE_DIR}" LIBRARY_DEPS "${OPENCV_ANDROID_LIB_DIR}" SDK_TARGET 11 "${ANDROID_SDK_TARGET}" NATIVE_DEPS ${native_deps})
+if(TARGET ${sample})
+  add_dependencies(opencv_android_examples ${sample})
+endif()

3rdparty/opencv-4.5.4/samples/android/face-detection/build.gradle.in

@@ -0,0 +1,43 @@
+apply plugin: 'com.android.application'
+
+android {
+    compileSdkVersion @ANDROID_COMPILE_SDK_VERSION@
+    defaultConfig {
+        applicationId "org.opencv.samples.facedetect"
+        minSdkVersion @ANDROID_MIN_SDK_VERSION@
+        targetSdkVersion @ANDROID_TARGET_SDK_VERSION@
+        versionCode 301
+        versionName "3.01"
+
+        externalNativeBuild {
+            cmake {
+                arguments "-DOpenCV_DIR=" + project(':opencv').projectDir + "/@ANDROID_PROJECT_JNI_PATH@"@OPENCV_ANDROID_CMAKE_EXTRA_ARGS@
+                targets "detection_based_tracker"
+            }
+        }
+    }
+    buildTypes {
+        release {
+            minifyEnabled false
+            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
+        }
+    }
+    sourceSets {
+        main {
+            java.srcDirs = @ANDROID_SAMPLE_JAVA_PATH@
+            aidl.srcDirs = @ANDROID_SAMPLE_JAVA_PATH@
+            res.srcDirs = @ANDROID_SAMPLE_RES_PATH@
+            manifest.srcFile '@ANDROID_SAMPLE_MANIFEST_PATH@'
+        }
+    }
+    externalNativeBuild {
+        cmake {
+             path '@ANDROID_SAMPLE_JNI_PATH@/CMakeLists.txt'
+        }
+    }
+}
+
+dependencies {
+    //implementation fileTree(dir: 'libs', include: ['*.jar'])
+    implementation project(':opencv')
+}

3rdparty/opencv-4.5.4/samples/android/face-detection/gradle/AndroidManifest.xml

@@ -0,0 +1,34 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+          package="org.opencv.samples.facedetect"
+>
+
+    <application
+        android:label="@string/app_name"
+        android:icon="@drawable/icon">
+
+        <activity android:name="FdActivity"
+                  android:label="@string/app_name"
+                  android:screenOrientation="landscape"
+                  android:configChanges="keyboardHidden|orientation">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+        </activity>
+    </application>
+
+    <supports-screens android:resizeable="true"
+                      android:smallScreens="true"
+                      android:normalScreens="true"
+                      android:largeScreens="true"
+                      android:anyDensity="true" />
+
+    <uses-permission android:name="android.permission.CAMERA"/>
+
+    <uses-feature android:name="android.hardware.camera" android:required="false"/>
+    <uses-feature android:name="android.hardware.camera.autofocus" android:required="false"/>
+    <uses-feature android:name="android.hardware.camera.front" android:required="false"/>
+    <uses-feature android:name="android.hardware.camera.front.autofocus" android:required="false"/>
+
+</manifest>

3rdparty/opencv-4.5.4/samples/android/face-detection/jni/Android.mk

@@ -0,0 +1,23 @@
+LOCAL_PATH := $(call my-dir)
+
+include $(CLEAR_VARS)
+
+#OPENCV_INSTALL_MODULES:=off
+#OPENCV_LIB_TYPE:=SHARED
+ifdef OPENCV_ANDROID_SDK
+  ifneq ("","$(wildcard $(OPENCV_ANDROID_SDK)/OpenCV.mk)")
+    include ${OPENCV_ANDROID_SDK}/OpenCV.mk
+  else
+    include ${OPENCV_ANDROID_SDK}/sdk/native/jni/OpenCV.mk
+  endif
+else
+  include ../../sdk/native/jni/OpenCV.mk
+endif
+
+LOCAL_SRC_FILES  := DetectionBasedTracker_jni.cpp
+LOCAL_C_INCLUDES += $(LOCAL_PATH)
+LOCAL_LDLIBS     += -llog -ldl
+
+LOCAL_MODULE     := detection_based_tracker
+
+include $(BUILD_SHARED_LIBRARY)

3rdparty/opencv-4.5.4/samples/android/face-detection/jni/Application.mk

@@ -0,0 +1,4 @@
+APP_STL := gnustl_static
+APP_CPPFLAGS := -frtti -fexceptions
+APP_ABI := armeabi-v7a
+APP_PLATFORM := android-8

3rdparty/opencv-4.5.4/samples/android/face-detection/jni/CMakeLists.txt

@@ -0,0 +1,15 @@
+cmake_minimum_required(VERSION 3.6)
+
+set(target detection_based_tracker)
+project(${target} CXX)
+
+set(ANDROID_OPENCV_COMPONENTS "opencv_java" CACHE STRING "")
+message(STATUS "ANDROID_ABI=${ANDROID_ABI}")
+find_package(OpenCV REQUIRED COMPONENTS ${ANDROID_OPENCV_COMPONENTS})
+
+file(GLOB srcs *.cpp *.c)
+file(GLOB hdrs *.hpp *.h)
+
+include_directories("${CMAKE_CURRENT_LIST_DIR}")
+add_library(${target} SHARED ${srcs} ${hdrs})
+target_link_libraries(${target} ${ANDROID_OPENCV_COMPONENTS})

3rdparty/opencv-4.5.4/samples/android/face-detection/jni/DetectionBasedTracker_jni.cpp

@@ -0,0 +1,251 @@
+#include <DetectionBasedTracker_jni.h>
+#include <opencv2/core.hpp>
+#include <opencv2/objdetect.hpp>
+
+#include <string>
+#include <vector>
+
+#include <android/log.h>
+
+#define LOG_TAG "FaceDetection/DetectionBasedTracker"
+#define LOGD(...) ((void)__android_log_print(ANDROID_LOG_DEBUG, LOG_TAG, __VA_ARGS__))
+
+using namespace std;
+using namespace cv;
+
+inline void vector_Rect_to_Mat(vector<Rect>& v_rect, Mat& mat)
+{
+    mat = Mat(v_rect, true);
+}
+
+class CascadeDetectorAdapter: public DetectionBasedTracker::IDetector
+{
+public:
+    CascadeDetectorAdapter(cv::Ptr<cv::CascadeClassifier> detector):
+            IDetector(),
+            Detector(detector)
+    {
+        LOGD("CascadeDetectorAdapter::Detect::Detect");
+        CV_Assert(detector);
+    }
+
+    void detect(const cv::Mat &Image, std::vector<cv::Rect> &objects)
+    {
+        LOGD("CascadeDetectorAdapter::Detect: begin");
+        LOGD("CascadeDetectorAdapter::Detect: scaleFactor=%.2f, minNeighbours=%d, minObjSize=(%dx%d), maxObjSize=(%dx%d)", scaleFactor, minNeighbours, minObjSize.width, minObjSize.height, maxObjSize.width, maxObjSize.height);
+        Detector->detectMultiScale(Image, objects, scaleFactor, minNeighbours, 0, minObjSize, maxObjSize);
+        LOGD("CascadeDetectorAdapter::Detect: end");
+    }
+
+    virtual ~CascadeDetectorAdapter()
+    {
+        LOGD("CascadeDetectorAdapter::Detect::~Detect");
+    }
+
+private:
+    CascadeDetectorAdapter();
+    cv::Ptr<cv::CascadeClassifier> Detector;
+};
+
+struct DetectorAgregator
+{
+    cv::Ptr<CascadeDetectorAdapter> mainDetector;
+    cv::Ptr<CascadeDetectorAdapter> trackingDetector;
+
+    cv::Ptr<DetectionBasedTracker> tracker;
+    DetectorAgregator(cv::Ptr<CascadeDetectorAdapter>& _mainDetector, cv::Ptr<CascadeDetectorAdapter>& _trackingDetector):
+            mainDetector(_mainDetector),
+            trackingDetector(_trackingDetector)
+    {
+        CV_Assert(_mainDetector);
+        CV_Assert(_trackingDetector);
+
+        DetectionBasedTracker::Parameters DetectorParams;
+        tracker = makePtr<DetectionBasedTracker>(mainDetector, trackingDetector, DetectorParams);
+    }
+};
+
+JNIEXPORT jlong JNICALL Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeCreateObject
+(JNIEnv * jenv, jclass, jstring jFileName, jint faceSize)
+{
+    LOGD("Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeCreateObject enter");
+    const char* jnamestr = jenv->GetStringUTFChars(jFileName, NULL);
+    string stdFileName(jnamestr);
+    jlong result = 0;
+
+    LOGD("Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeCreateObject");
+
+    try
+    {
+        cv::Ptr<CascadeDetectorAdapter> mainDetector = makePtr<CascadeDetectorAdapter>(
+            makePtr<CascadeClassifier>(stdFileName));
+        cv::Ptr<CascadeDetectorAdapter> trackingDetector = makePtr<CascadeDetectorAdapter>(
+            makePtr<CascadeClassifier>(stdFileName));
+        result = (jlong)new DetectorAgregator(mainDetector, trackingDetector);
+        if (faceSize > 0)
+        {
+            mainDetector->setMinObjectSize(Size(faceSize, faceSize));
+            //trackingDetector->setMinObjectSize(Size(faceSize, faceSize));
+        }
+    }
+    catch(const cv::Exception& e)
+    {
+        LOGD("nativeCreateObject caught cv::Exception: %s", e.what());
+        jclass je = jenv->FindClass("org/opencv/core/CvException");
+        if(!je)
+            je = jenv->FindClass("java/lang/Exception");
+        jenv->ThrowNew(je, e.what());
+    }
+    catch (...)
+    {
+        LOGD("nativeCreateObject caught unknown exception");
+        jclass je = jenv->FindClass("java/lang/Exception");
+        jenv->ThrowNew(je, "Unknown exception in JNI code of DetectionBasedTracker.nativeCreateObject()");
+        return 0;
+    }
+
+    LOGD("Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeCreateObject exit");
+    return result;
+}
+
+JNIEXPORT void JNICALL Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeDestroyObject
+(JNIEnv * jenv, jclass, jlong thiz)
+{
+    LOGD("Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeDestroyObject");
+
+    try
+    {
+        if(thiz != 0)
+        {
+            ((DetectorAgregator*)thiz)->tracker->stop();
+            delete (DetectorAgregator*)thiz;
+        }
+    }
+    catch(const cv::Exception& e)
+    {
+        LOGD("nativeestroyObject caught cv::Exception: %s", e.what());
+        jclass je = jenv->FindClass("org/opencv/core/CvException");
+        if(!je)
+            je = jenv->FindClass("java/lang/Exception");
+        jenv->ThrowNew(je, e.what());
+    }
+    catch (...)
+    {
+        LOGD("nativeDestroyObject caught unknown exception");
+        jclass je = jenv->FindClass("java/lang/Exception");
+        jenv->ThrowNew(je, "Unknown exception in JNI code of DetectionBasedTracker.nativeDestroyObject()");
+    }
+    LOGD("Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeDestroyObject exit");
+}
+
+JNIEXPORT void JNICALL Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeStart
+(JNIEnv * jenv, jclass, jlong thiz)
+{
+    LOGD("Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeStart");
+
+    try
+    {
+        ((DetectorAgregator*)thiz)->tracker->run();
+    }
+    catch(const cv::Exception& e)
+    {
+        LOGD("nativeStart caught cv::Exception: %s", e.what());
+        jclass je = jenv->FindClass("org/opencv/core/CvException");
+        if(!je)
+            je = jenv->FindClass("java/lang/Exception");
+        jenv->ThrowNew(je, e.what());
+    }
+    catch (...)
+    {
+        LOGD("nativeStart caught unknown exception");
+        jclass je = jenv->FindClass("java/lang/Exception");
+        jenv->ThrowNew(je, "Unknown exception in JNI code of DetectionBasedTracker.nativeStart()");
+    }
+    LOGD("Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeStart exit");
+}
+
+JNIEXPORT void JNICALL Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeStop
+(JNIEnv * jenv, jclass, jlong thiz)
+{
+    LOGD("Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeStop");
+
+    try
+    {
+        ((DetectorAgregator*)thiz)->tracker->stop();
+    }
+    catch(const cv::Exception& e)
+    {
+        LOGD("nativeStop caught cv::Exception: %s", e.what());
+        jclass je = jenv->FindClass("org/opencv/core/CvException");
+        if(!je)
+            je = jenv->FindClass("java/lang/Exception");
+        jenv->ThrowNew(je, e.what());
+    }
+    catch (...)
+    {
+        LOGD("nativeStop caught unknown exception");
+        jclass je = jenv->FindClass("java/lang/Exception");
+        jenv->ThrowNew(je, "Unknown exception in JNI code of DetectionBasedTracker.nativeStop()");
+    }
+    LOGD("Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeStop exit");
+}
+
+JNIEXPORT void JNICALL Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeSetFaceSize
+(JNIEnv * jenv, jclass, jlong thiz, jint faceSize)
+{
+    LOGD("Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeSetFaceSize -- BEGIN");
+
+    try
+    {
+        if (faceSize > 0)
+        {
+            ((DetectorAgregator*)thiz)->mainDetector->setMinObjectSize(Size(faceSize, faceSize));
+            //((DetectorAgregator*)thiz)->trackingDetector->setMinObjectSize(Size(faceSize, faceSize));
+        }
+    }
+    catch(const cv::Exception& e)
+    {
+        LOGD("nativeStop caught cv::Exception: %s", e.what());
+        jclass je = jenv->FindClass("org/opencv/core/CvException");
+        if(!je)
+            je = jenv->FindClass("java/lang/Exception");
+        jenv->ThrowNew(je, e.what());
+    }
+    catch (...)
+    {
+        LOGD("nativeSetFaceSize caught unknown exception");
+        jclass je = jenv->FindClass("java/lang/Exception");
+        jenv->ThrowNew(je, "Unknown exception in JNI code of DetectionBasedTracker.nativeSetFaceSize()");
+    }
+    LOGD("Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeSetFaceSize -- END");
+}
+
+
+JNIEXPORT void JNICALL Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeDetect
+(JNIEnv * jenv, jclass, jlong thiz, jlong imageGray, jlong faces)
+{
+    LOGD("Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeDetect");
+
+    try
+    {
+        vector<Rect> RectFaces;
+        ((DetectorAgregator*)thiz)->tracker->process(*((Mat*)imageGray));
+        ((DetectorAgregator*)thiz)->tracker->getObjects(RectFaces);
+        *((Mat*)faces) = Mat(RectFaces, true);
+    }
+    catch(const cv::Exception& e)
+    {
+        LOGD("nativeCreateObject caught cv::Exception: %s", e.what());
+        jclass je = jenv->FindClass("org/opencv/core/CvException");
+        if(!je)
+            je = jenv->FindClass("java/lang/Exception");
+        jenv->ThrowNew(je, e.what());
+    }
+    catch (...)
+    {
+        LOGD("nativeDetect caught unknown exception");
+        jclass je = jenv->FindClass("java/lang/Exception");
+        jenv->ThrowNew(je, "Unknown exception in JNI code DetectionBasedTracker.nativeDetect()");
+    }
+    LOGD("Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeDetect END");
+}

3rdparty/opencv-4.5.4/samples/android/face-detection/jni/DetectionBasedTracker_jni.h

@@ -0,0 +1,61 @@
+/* DO NOT EDIT THIS FILE - it is machine generated */
+#include <jni.h>
+/* Header for class org_opencv_samples_fd_DetectionBasedTracker */
+
+#ifndef _Included_org_opencv_samples_fd_DetectionBasedTracker
+#define _Included_org_opencv_samples_fd_DetectionBasedTracker
+#ifdef __cplusplus
+extern "C" {
+#endif
+/*
+ * Class:     org_opencv_samples_fd_DetectionBasedTracker
+ * Method:    nativeCreateObject
+ * Signature: (Ljava/lang/String;F)J
+ */
+JNIEXPORT jlong JNICALL Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeCreateObject
+  (JNIEnv *, jclass, jstring, jint);
+
+/*
+ * Class:     org_opencv_samples_fd_DetectionBasedTracker
+ * Method:    nativeDestroyObject
+ * Signature: (J)V
+ */
+JNIEXPORT void JNICALL Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeDestroyObject
+  (JNIEnv *, jclass, jlong);
+
+/*
+ * Class:     org_opencv_samples_fd_DetectionBasedTracker
+ * Method:    nativeStart
+ * Signature: (J)V
+ */
+JNIEXPORT void JNICALL Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeStart
+  (JNIEnv *, jclass, jlong);
+
+/*
+ * Class:     org_opencv_samples_fd_DetectionBasedTracker
+ * Method:    nativeStop
+ * Signature: (J)V
+ */
+JNIEXPORT void JNICALL Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeStop
+  (JNIEnv *, jclass, jlong);
+
+  /*
+   * Class:     org_opencv_samples_fd_DetectionBasedTracker
+   * Method:    nativeSetFaceSize
+   * Signature: (JI)V
+   */
+  JNIEXPORT void JNICALL Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeSetFaceSize
+  (JNIEnv *, jclass, jlong, jint);
+
+/*
+ * Class:     org_opencv_samples_fd_DetectionBasedTracker
+ * Method:    nativeDetect
+ * Signature: (JJJ)V
+ */
+JNIEXPORT void JNICALL Java_org_opencv_samples_facedetect_DetectionBasedTracker_nativeDetect
+  (JNIEnv *, jclass, jlong, jlong, jlong);
+
+#ifdef __cplusplus
+}
+#endif
+#endif

3rdparty/opencv-4.5.4/samples/android/face-detection/res/layout/face_detect_surface_view.xml

@@ -0,0 +1,11 @@
+<LinearLayout 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" >
+
+    <org.opencv.android.JavaCameraView
+        android:layout_width="fill_parent"
+        android:layout_height="fill_parent"
+        android:id="@+id/fd_activity_surface_view" />
+
+</LinearLayout>

3rdparty/opencv-4.5.4/samples/android/face-detection/res/values/strings.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <string name="app_name">OCV Face Detection</string>
+</resources>

3rdparty/opencv-4.5.4/samples/android/face-detection/src/org/opencv/samples/facedetect/DetectionBasedTracker.java

@@ -0,0 +1,41 @@
+package org.opencv.samples.facedetect;
+
+import org.opencv.core.Mat;
+import org.opencv.core.MatOfRect;
+
+public class DetectionBasedTracker
+{
+    public DetectionBasedTracker(String cascadeName, int minFaceSize) {
+        mNativeObj = nativeCreateObject(cascadeName, minFaceSize);
+    }
+
+    public void start() {
+        nativeStart(mNativeObj);
+    }
+
+    public void stop() {
+        nativeStop(mNativeObj);
+    }
+
+    public void setMinFaceSize(int size) {
+        nativeSetFaceSize(mNativeObj, size);
+    }
+
+    public void detect(Mat imageGray, MatOfRect faces) {
+        nativeDetect(mNativeObj, imageGray.getNativeObjAddr(), faces.getNativeObjAddr());
+    }
+
+    public void release() {
+        nativeDestroyObject(mNativeObj);
+        mNativeObj = 0;
+    }
+
+    private long mNativeObj = 0;
+
+    private static native long nativeCreateObject(String cascadeName, int minFaceSize);
+    private static native void nativeDestroyObject(long thiz);
+    private static native void nativeStart(long thiz);
+    private static native void nativeStop(long thiz);
+    private static native void nativeSetFaceSize(long thiz, int size);
+    private static native void nativeDetect(long thiz, long inputImage, long faces);
+}

3rdparty/opencv-4.5.4/samples/android/face-detection/src/org/opencv/samples/facedetect/FdActivity.java

@@ -0,0 +1,259 @@
+package org.opencv.samples.facedetect;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Collections;
+import java.util.List;
+
+import org.opencv.android.BaseLoaderCallback;
+import org.opencv.android.CameraActivity;
+import org.opencv.android.CameraBridgeViewBase.CvCameraViewFrame;
+import org.opencv.android.LoaderCallbackInterface;
+import org.opencv.android.OpenCVLoader;
+import org.opencv.core.Core;
+import org.opencv.core.Mat;
+import org.opencv.core.MatOfRect;
+import org.opencv.core.Rect;
+import org.opencv.core.Scalar;
+import org.opencv.core.Size;
+import org.opencv.android.CameraBridgeViewBase;
+import org.opencv.android.CameraBridgeViewBase.CvCameraViewListener2;
+import org.opencv.objdetect.CascadeClassifier;
+import org.opencv.imgproc.Imgproc;
+
+import android.app.Activity;
+import android.content.Context;
+import android.os.Bundle;
+import android.util.Log;
+import android.view.Menu;
+import android.view.MenuItem;
+import android.view.WindowManager;
+
+public class FdActivity extends CameraActivity implements CvCameraViewListener2 {
+
+    private static final String    TAG                 = "OCVSample::Activity";
+    private static final Scalar    FACE_RECT_COLOR     = new Scalar(0, 255, 0, 255);
+    public static final int        JAVA_DETECTOR       = 0;
+    public static final int        NATIVE_DETECTOR     = 1;
+
+    private MenuItem               mItemFace50;
+    private MenuItem               mItemFace40;
+    private MenuItem               mItemFace30;
+    private MenuItem               mItemFace20;
+    private MenuItem               mItemType;
+
+    private Mat                    mRgba;
+    private Mat                    mGray;
+    private File                   mCascadeFile;
+    private CascadeClassifier      mJavaDetector;
+    private DetectionBasedTracker  mNativeDetector;
+
+    private int                    mDetectorType       = JAVA_DETECTOR;
+    private String[]               mDetectorName;
+
+    private float                  mRelativeFaceSize   = 0.2f;
+    private int                    mAbsoluteFaceSize   = 0;
+
+    private CameraBridgeViewBase   mOpenCvCameraView;
+
+    private BaseLoaderCallback  mLoaderCallback = new BaseLoaderCallback(this) {
+        @Override
+        public void onManagerConnected(int status) {
+            switch (status) {
+                case LoaderCallbackInterface.SUCCESS:
+                {
+                    Log.i(TAG, "OpenCV loaded successfully");
+
+                    // Load native library after(!) OpenCV initialization
+                    System.loadLibrary("detection_based_tracker");
+
+                    try {
+                        // load cascade file from application resources
+                        InputStream is = getResources().openRawResource(R.raw.lbpcascade_frontalface);
+                        File cascadeDir = getDir("cascade", Context.MODE_PRIVATE);
+                        mCascadeFile = new File(cascadeDir, "lbpcascade_frontalface.xml");
+                        FileOutputStream os = new FileOutputStream(mCascadeFile);
+
+                        byte[] buffer = new byte[4096];
+                        int bytesRead;
+                        while ((bytesRead = is.read(buffer)) != -1) {
+                            os.write(buffer, 0, bytesRead);
+                        }
+                        is.close();
+                        os.close();
+
+                        mJavaDetector = new CascadeClassifier(mCascadeFile.getAbsolutePath());
+                        if (mJavaDetector.empty()) {
+                            Log.e(TAG, "Failed to load cascade classifier");
+                            mJavaDetector = null;
+                        } else
+                            Log.i(TAG, "Loaded cascade classifier from " + mCascadeFile.getAbsolutePath());
+
+                        mNativeDetector = new DetectionBasedTracker(mCascadeFile.getAbsolutePath(), 0);
+
+                        cascadeDir.delete();
+
+                    } catch (IOException e) {
+                        e.printStackTrace();
+                        Log.e(TAG, "Failed to load cascade. Exception thrown: " + e);
+                    }
+
+                    mOpenCvCameraView.enableView();
+                } break;
+                default:
+                {
+                    super.onManagerConnected(status);
+                } break;
+            }
+        }
+    };
+
+    public FdActivity() {
+        mDetectorName = new String[2];
+        mDetectorName[JAVA_DETECTOR] = "Java";
+        mDetectorName[NATIVE_DETECTOR] = "Native (tracking)";
+
+        Log.i(TAG, "Instantiated new " + this.getClass());
+    }
+
+    /** Called when the activity is first created. */
+    @Override
+    public void onCreate(Bundle savedInstanceState) {
+        Log.i(TAG, "called onCreate");
+        super.onCreate(savedInstanceState);
+        getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
+
+        setContentView(R.layout.face_detect_surface_view);
+
+        mOpenCvCameraView = (CameraBridgeViewBase) findViewById(R.id.fd_activity_surface_view);
+        mOpenCvCameraView.setVisibility(CameraBridgeViewBase.VISIBLE);
+        mOpenCvCameraView.setCvCameraViewListener(this);
+    }
+
+    @Override
+    public void onPause()
+    {
+        super.onPause();
+        if (mOpenCvCameraView != null)
+            mOpenCvCameraView.disableView();
+    }
+
+    @Override
+    public void onResume()
+    {
+        super.onResume();
+        if (!OpenCVLoader.initDebug()) {
+            Log.d(TAG, "Internal OpenCV library not found. Using OpenCV Manager for initialization");
+            OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_3_0_0, this, mLoaderCallback);
+        } else {
+            Log.d(TAG, "OpenCV library found inside package. Using it!");
+            mLoaderCallback.onManagerConnected(LoaderCallbackInterface.SUCCESS);
+        }
+    }
+
+    @Override
+    protected List<? extends CameraBridgeViewBase> getCameraViewList() {
+        return Collections.singletonList(mOpenCvCameraView);
+    }
+
+    public void onDestroy() {
+        super.onDestroy();
+        mOpenCvCameraView.disableView();
+    }
+
+    public void onCameraViewStarted(int width, int height) {
+        mGray = new Mat();
+        mRgba = new Mat();
+    }
+
+    public void onCameraViewStopped() {
+        mGray.release();
+        mRgba.release();
+    }
+
+    public Mat onCameraFrame(CvCameraViewFrame inputFrame) {
+
+        mRgba = inputFrame.rgba();
+        mGray = inputFrame.gray();
+
+        if (mAbsoluteFaceSize == 0) {
+            int height = mGray.rows();
+            if (Math.round(height * mRelativeFaceSize) > 0) {
+                mAbsoluteFaceSize = Math.round(height * mRelativeFaceSize);
+            }
+            mNativeDetector.setMinFaceSize(mAbsoluteFaceSize);
+        }
+
+        MatOfRect faces = new MatOfRect();
+
+        if (mDetectorType == JAVA_DETECTOR) {
+            if (mJavaDetector != null)
+                mJavaDetector.detectMultiScale(mGray, faces, 1.1, 2, 2, // TODO: objdetect.CV_HAAR_SCALE_IMAGE
+                        new Size(mAbsoluteFaceSize, mAbsoluteFaceSize), new Size());
+        }
+        else if (mDetectorType == NATIVE_DETECTOR) {
+            if (mNativeDetector != null)
+                mNativeDetector.detect(mGray, faces);
+        }
+        else {
+            Log.e(TAG, "Detection method is not selected!");
+        }
+
+        Rect[] facesArray = faces.toArray();
+        for (int i = 0; i < facesArray.length; i++)
+            Imgproc.rectangle(mRgba, facesArray[i].tl(), facesArray[i].br(), FACE_RECT_COLOR, 3);
+
+        return mRgba;
+    }
+
+    @Override
+    public boolean onCreateOptionsMenu(Menu menu) {
+        Log.i(TAG, "called onCreateOptionsMenu");
+        mItemFace50 = menu.add("Face size 50%");
+        mItemFace40 = menu.add("Face size 40%");
+        mItemFace30 = menu.add("Face size 30%");
+        mItemFace20 = menu.add("Face size 20%");
+        mItemType   = menu.add(mDetectorName[mDetectorType]);
+        return true;
+    }
+
+    @Override
+    public boolean onOptionsItemSelected(MenuItem item) {
+        Log.i(TAG, "called onOptionsItemSelected; selected item: " + item);
+        if (item == mItemFace50)
+            setMinFaceSize(0.5f);
+        else if (item == mItemFace40)
+            setMinFaceSize(0.4f);
+        else if (item == mItemFace30)
+            setMinFaceSize(0.3f);
+        else if (item == mItemFace20)
+            setMinFaceSize(0.2f);
+        else if (item == mItemType) {
+            int tmpDetectorType = (mDetectorType + 1) % mDetectorName.length;
+            item.setTitle(mDetectorName[tmpDetectorType]);
+            setDetectorType(tmpDetectorType);
+        }
+        return true;
+    }
+
+    private void setMinFaceSize(float faceSize) {
+        mRelativeFaceSize = faceSize;
+        mAbsoluteFaceSize = 0;
+    }
+
+    private void setDetectorType(int type) {
+        if (mDetectorType != type) {
+            mDetectorType = type;
+
+            if (type == NATIVE_DETECTOR) {
+                Log.i(TAG, "Detection Based Tracker enabled");
+                mNativeDetector.start();
+            } else {
+                Log.i(TAG, "Cascade detector enabled");
+                mNativeDetector.stop();
+            }
+        }
+    }
+}