[Android Studio] Using NDK to call OpenCV

NDK纔是Android開發通向超高薪之路。（這句話，彷佛四年前有云）

難點在於經常使用的non-free module (sift and surf)

 

unsw@unsw-UX303UB$ pwd /home/unsw/Android/5-android/NDKTest/app/src/main unsw@unsw-UX303UB$ javah -d jni -classpath ../../build/intermediates/classes/debug com.example.unsw.ndktest.NativeClass

 

生成了jni目錄, 而且有了一個.h文件。

---

 

 jni目錄下添加 

1. 經過.h文件複製粘貼出個.c文件，這樣少輸入這麼長的名字。

 

2. 而後，把.h的內容改成.c須要的形式。

/* DO NOT EDIT THIS FILE - it is machine generated */ #include <jni.h>
/* Header for class com_example_unsw_ndktest_NativeClass */ #ifndef _Included_com_example_unsw_ndktest_NativeClass #define _Included_com_example_unsw_ndktest_NativeClass #ifdef __cplusplus extern "C" { #endif /* * Class: com_example_unsw_ndktest_NativeClass * Method: getMessageFromJNI * Signature: ()Ljava/lang/String; */ JNIEXPORT jstring JNICALL Java_com_example_unsw_ndktest_NativeClass_getMessageFromJNI (JNIEnv *, jclass);
// 改成以下所示：(其餘刪除)
 #include <com_example_unsw_ndktest_NativeClass.h> JNIEXPORT jstring JNICALL Java_com_example_unsw_ndktest_NativeClass_getMessageFromJNI (JNIEnv *env, jclass obj) { return env->NewStringUTF("This is message from JNI"); }

#ifdef __cplusplus } #endif #endif

 

3. 添加到此處後，能夠嘗試編譯下，應該不會報錯。

gradle.properties添加：
　　android.useDeprecatedNdk=true

 

4. 繼續添加.mk文件：

Android.mk

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_SRC_FILES := com_example_unsw_ndktest_NativeClass.cpp

LOCAL_LDLIBS += -llog
LOCAL_MODULE := MyLib


include $(BUILD_SHARED_LIBRARY)

Application.mk

APP_STL := gnustl_static
APP_CPPFLAGS := -frtti -fexceptions
APP_ABI := armeabi-v7a　　//若是是本地模擬器，則爲x86
APP_PLATFORM := android-23

 

5. Compile, generate *.so

 

6. Just use your baby function.

public class MainActivity extends AppCompatActivity { static { System.loadLibrary("MyLibs"); } @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); ((TextView) findViewById(R.id.textView)).setText(NativeClass.getMessageFromJNI()); } }

 

 

 

若c++調用的是OpenCV lib，以下示範 

---

  

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
#include <stdio.h> #include <opencv2/opencv.hpp> #include "opencv2/nonfree/nonfree.hpp"

using namespace cv;
using namespace std;
/* Header for class com_example_unsw_jeff_OpencvNativeClass */

#ifndef _Included_com_example_unsw_jeff_OpencvNativeClass
#define _Included_com_example_unsw_jeff_OpencvNativeClass
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_example_unsw_jeff_OpencvNativeClass
 * Method:    convertGray
 * Signature: (JJ)I
 */
int toGray(Mat img, Mat& gray);

JNIEXPORT jint JNICALL Java_com_example_unsw_jeff_OpencvNativeClass_convertGray
  (JNIEnv *, jclass, jlong, jlong);

#ifdef __cplusplus
}
#endif
#endif

 

　　

但要注意一個問題：Nonfree Module (SIFT, SURF) 

---

參見以下：

OpenCV & Android

• Tutorial - part 1: Using OpenCV Nonfree Module (SIFT, SURF) in Android NDK Projects (可用)

• Tutorial - part 2: Use OpenCV Nonfree module (SIFT, SURF) in Android Applications via JNI （可用）

Kornel的總結：（opencv 2.4.10）

http://stackoverflow.com/questions/28510045/undefined-reference-to-cvinitmodule-nonfree-in-android
直接使用現成lib的tutor: https://www.youtube.com/watch?v=cLK9CjQ-pNI
做者代碼隱藏在了這裏：https://dmigit.uqtr.ca/u/nguidjol

 

1. 工程下新建文件夾 libraries/，並拷貝過來 java文件夾 in opencv-for-android。

unsw@unsw-UX303UB$ cp ./OpenCV-2.4.9-android-sdk/sdk/
etc/    java/   native/

Copy "java" to libraries and change its name to "opencv"

unsw@unsw-UX303UB$ pwd
/home/unsw/Programmer/5-android/nonfree_model

unsw@unsw-UX303UB$ ls
app           gradle             gradlew.bat       nonfree_model.iml
build         gradle.properties  libraries         settings.gradle
build.gradle  gradlew            local.properties

unsw@unsw-UX303UB$ ls libraries/
libraries.iml  opencv

效果以下：

 

2. opencv文件夾下 create build.gradle.

apply plugin: 'com.android.library'

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:2.2.3'
    }
}

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.2"

    defaultConfig {
        minSdkVersion 23
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"
    }

    sourceSets {
        main {
            manifest.srcFile 'AndroidManifest.xml'
            java.srcDirs = ['src']
            resources.srcDirs = ['src']
            res.srcDirs = ['res']
            aidl.srcDirs = ['src']
        }
    }
}

build.gradle

3. settings.gradle添加庫

include ':app'
include ':libraries:opencv'  //add.

以後，Project structure即可加載libraries:opencv 模塊。

 

4. 添加sift操做java文件

package com.example.unsw.nonfree_model;

import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.media.FaceDetector;
import android.net.Uri;
import android.os.Bundle;
import android.provider.MediaStore;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.VideoView;

import org.opencv.android.Utils;
import org.opencv.core.Mat;
import org.opencv.core.MatOfKeyPoint;
import org.opencv.features2d.FeatureDetector;
import org.opencv.features2d.Features2d;
import org.opencv.imgproc.Imgproc;

public class MainActivity extends AppCompatActivity {

    static {
        System.loadLibrary("opencv_java");
        System.loadLibrary("nonfree");
    }

    private ImageView imageView;
    private Bitmap inputImage; // make bitmap from image resource
    private FeatureDetector detector = FeatureDetector.create(FeatureDetector.SIFT);

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        inputImage = BitmapFactory.decodeResource(getResources(), R.drawable.test);

        setContentView(R.layout.activity_main);
        imageView = (ImageView) this.findViewById(R.id.imageView);

        sift();
    }

    public void onResume(){
        super.onResume();
    }

    public void sift(){
        Mat rgba = new Mat();
        Utils.bitmapToMat(inputImage,rgba);
        MatOfKeyPoint keyPoints = new MatOfKeyPoint();
        Imgproc.cvtColor(rgba, rgba, Imgproc.COLOR_RGBA2GRAY);
        detector.detect(rgba, keyPoints);
        Features2d.drawKeypoints(rgba, keyPoints, rgba);
        Utils.matToBitmap(rgba, inputImage);
        imageView.setImageBitmap(inputImage);
    }
}

以及相對應的 layout。

 

5. 添加現成的 .so 

新建jniLibs，給jniLibs各個目錄內添加.so。

 

效果圖：(可見sift的特徵點)

 

  

---

 -- 如何生成本身的 .so --

 

　　（1）爲使OpenCV-2.4.9-android-sdk完整，添加了OpenCV-2.4.9的nonfree文件夾。

unsw@unsw-UX303UB$ ls opencv-2.4.9/modules/nonfree/include/opencv2/nonfree/ features2d.hpp  gpu.hpp         nonfree.hpp     ocl.hpp

unsw@unsw-UX303UB$ ls OpenCV-2.4.9-android-sdk/sdk/native/jni/include/opencv2/nonfree/ features2d.hpp nonfree.hpp

  

（2）新工程：MyApplication下建立文件夾：nonfree_opencv_android/jni, 其下也添加OpenCV-2.4.9的modules/nonfree/src/* 的內容。

unsw@unsw-UX303UB$ pwd

/home/unsw/Programmer/5-android/MyApplication/nonfree_opencv_android 
unsw@unsw-UX303UB$ ls jni  libs obj //ndk-build後生成的。 
// jni 添加如下內容：
unsw@unsw-UX303UB$ ls ~/Android/opencv-2.4.9/modules/nonfree/src/
cuda/ opencl/ sift.cpp surf_gpu.cpp
nonfree_init.cpp precomp.hpp surf.cpp surf_ocl.cpp

修改文件裏的內容，按照報錯提示去掉ocl相關的部分便可。

unsw@unsw-UX303UB$ ~/Android/Sdk/ndk-bundle/ndk-build 
[x86] Compile++      : nonfree <= nonfree_init.cpp
In file included from jni/nonfree_init.cpp:43:
jni/precomp.hpp:46:10: fatal error: 'cvconfig.h' file not found
#include "cvconfig.h"
         ^
1 error generated.
make: *** [obj/local/x86/objs/nonfree/nonfree_init.o] Error 1

unsw@unsw-UX303UB$ ~/Android/Sdk/ndk-bundle/ndk-build 
[x86] Compile++      : nonfree <= nonfree_init.cpp
jni/nonfree_init.cpp:69:19: error: unknown type name 'SURF_OCL'
CV_INIT_ALGORITHM(SURF_OCL, "Feature2D.SURF_OCL",
                  ^
jni/nonfree_init.cpp:69:19: error: use of undeclared identifier 'SURF_OCL'
2 errors generated.
make: *** [obj/local/x86/objs/nonfree/nonfree_init.o] Error 1

Error處理

 

（3）再添加Android.mk和Application.mk，編譯便可。

APP_ABI := x86
APP_STL := gnustl_static
APP_CPPFLAGS := -frtti -fexceptions
APP_PLATFORM := android-23

Application.mk

LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)
OPENCV_INSTALL_MODULES:=on
OPENCV_CAMERA_MODULES:=off
include /home/unsw/Android/OpenCV-2.4.9-android-sdk/sdk/native/jni/OpenCV.mk

LOCAL_C_INCLUDES:= /home/unsw/Android/OpenCV-2.4.9-android-sdk/sdk/native/jni/include
LOCAL_MODULE    := nonfree
LOCAL_CFLAGS    := -Werror -O3 -ffast-math
LOCAL_LDLIBS    += -llog

LOCAL_SRC_FILES := nonfree_init.cpp \
 sift.cpp \
 surf.cpp
include $(BUILD_SHARED_LIBRARY)

Android.mk

Compile:

unsw@unsw-UX303UB$ ~/Android/Sdk/ndk-bundle/ndk-build 
[x86] Compile++      : nonfree <= nonfree_init.cpp
[x86] Compile++      : nonfree <= sift.cpp
[x86] Compile++      : nonfree <= surf.cpp
[x86] Prebuilt       : libopencv_java.so <= /home/unsw/Android/OpenCV-2.4.9-android-sdk/sdk/native/jni/../libs/x86/
[x86] SharedLibrary  : libnonfree.so
[x86] Install        : libnonfree.so => libs/x86/libnonfree.so
[x86] Install        : libopencv_java.so => libs/x86/libopencv_java.so

　　Success!