简介

在移动开发中，如果我们要实现一些图像处理相关的功能，难免要用到OpenCV。而OpenCV是用c++开发的。我们在Android中，需要使用jni的方法去使用它。

引入配置

我们引入jni开发的基本配置方法，已经在另一篇博客中介绍过了，不再赘述。这一次我们无非是要引入第三方的c++库。

首先，我们找到或新建jniLibs文件夹，然后将依赖的动态库和静态库（路径为OpenCV-android-sdk\sdk\native\libs）拷贝到\src\main\jniLibs下面。

然后，找到cpp文件夹。将include文件夹（路径OpenCV-android-sdk\sdk\native\jni\include）拷贝到cpp（路径\app\src\main\cpp）文件夹里。

接着，我们需要引入c++的相关支持。在module的build.gradle里面加入：

externalNativeBuild {
    cmake {
        //arguments  '-DANDROID_TOOLCHAIN=clang', '-DANDROID_STL=gnustl_static'
        cppFlags "-std=c++11","-frtti", "-fexceptions"
    }
}
ndk{
    abiFilters 'armeabi-v7a'
}

最后，我们需要在CMakeLists.txt中，加入opencv相关的声明。由于配置比较复杂，在此直接将demo的CMakeLists.txt的内容贴到这里。

# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html

# Sets the minimum version of CMake required to build the native library.

cmake_minimum_required(VERSION 3.4.1)

# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.

set(CMAKE_VERBOSE_MAKEFILE on)
set(libs "${CMAKE_SOURCE_DIR}/src/main/jniLibs")
include_directories(${CMAKE_SOURCE_DIR}/src/main/cpp/include)

add_library(libopencv_java3 SHARED IMPORTED )
set_target_properties(libopencv_java3 PROPERTIES
    IMPORTED_LOCATION "${libs}/${ANDROID_ABI}/libopencv_java3.so")

add_library(libopencv_calib3d STATIC IMPORTED )
set_target_properties(libopencv_calib3d PROPERTIES
    IMPORTED_LOCATION "${libs}/${ANDROID_ABI}/libopencv_calib3d.a")

add_library(libopencv_core STATIC IMPORTED )
set_target_properties(libopencv_core PROPERTIES
    IMPORTED_LOCATION "${libs}/${ANDROID_ABI}/libopencv_core.a")

add_library(libopencv_features2d STATIC IMPORTED )
set_target_properties(libopencv_features2d PROPERTIES
    IMPORTED_LOCATION "${libs}/${ANDROID_ABI}/libopencv_features2d.a")

add_library(libopencv_flann STATIC IMPORTED )
set_target_properties(libopencv_flann PROPERTIES
    IMPORTED_LOCATION "${libs}/${ANDROID_ABI}/libopencv_flann.a")

add_library(libopencv_highgui STATIC IMPORTED )
set_target_properties(libopencv_highgui PROPERTIES
    IMPORTED_LOCATION "${libs}/${ANDROID_ABI}/libopencv_highgui.a")

add_library(libopencv_imgcodecs STATIC IMPORTED )
set_target_properties(libopencv_imgcodecs PROPERTIES
    IMPORTED_LOCATION "${libs}/${ANDROID_ABI}/libopencv_imgcodecs.a")

add_library(libopencv_imgproc STATIC IMPORTED )
set_target_properties(libopencv_imgproc PROPERTIES
    IMPORTED_LOCATION "${libs}/${ANDROID_ABI}/libopencv_imgproc.a")

add_library(libopencv_ml STATIC IMPORTED )
set_target_properties(libopencv_ml PROPERTIES
    IMPORTED_LOCATION "${libs}/${ANDROID_ABI}/libopencv_ml.a")

add_library(libopencv_objdetect STATIC IMPORTED )
set_target_properties(libopencv_objdetect PROPERTIES
    IMPORTED_LOCATION "${libs}/${ANDROID_ABI}/libopencv_objdetect.a")

add_library(libopencv_photo STATIC IMPORTED )
set_target_properties(libopencv_photo PROPERTIES
    IMPORTED_LOCATION "${libs}/${ANDROID_ABI}/libopencv_photo.a")

add_library(libopencv_shape STATIC IMPORTED )
set_target_properties(libopencv_shape PROPERTIES
    IMPORTED_LOCATION "${libs}/${ANDROID_ABI}/libopencv_shape.a")

add_library(libopencv_stitching STATIC IMPORTED )
set_target_properties(libopencv_stitching PROPERTIES
    IMPORTED_LOCATION "${libs}/${ANDROID_ABI}/libopencv_stitching.a")

add_library(libopencv_superres STATIC IMPORTED )
set_target_properties(libopencv_superres PROPERTIES
    IMPORTED_LOCATION "${libs}/${ANDROID_ABI}/libopencv_superres.a")

add_library(libopencv_video STATIC IMPORTED )
set_target_properties(libopencv_video PROPERTIES
    IMPORTED_LOCATION "${libs}/${ANDROID_ABI}/libopencv_video.a")

add_library(libopencv_videoio STATIC IMPORTED )
set_target_properties(libopencv_videoio PROPERTIES
    IMPORTED_LOCATION "${libs}/${ANDROID_ABI}/libopencv_videoio.a")

add_library(libopencv_videostab STATIC IMPORTED )
set_target_properties(libopencv_videostab PROPERTIES
    IMPORTED_LOCATION "${libs}/${ANDROID_ABI}/libopencv_videostab.a")

add_library(libopencv_ts STATIC IMPORTED )
set_target_properties(libopencv_ts PROPERTIES
    IMPORTED_LOCATION "${libs}/${ANDROID_ABI}/libopencv_ts.a")

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++11 -fexceptions -frtti")

#include_directories(D:/Projects/Android/CLMAndroid/OpenCV-android-sdk/sdk/native/jni/include )
#set(OpenCV_DIR D:/Projects/Android/CLMAndroid/OpenCV-android-sdk/sdk/native/jni)
#find_package(OpenCV REQUIRED)
#target_link_libraries(${OpenCV_LIBS})

add_library( # Sets the name of the library.
             native-lib

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
             src/main/cpp/native-lib.cpp )

# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.

find_library( # Sets the name of the path variable.
              log-lib

              # Specifies the name of the NDK library that
              # you want CMake to locate.
              log )

# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.

target_link_libraries( # Specifies the target library.
                       native-lib android log
    libopencv_java3 libopencv_calib3d libopencv_core libopencv_features2d libopencv_flann libopencv_highgui libopencv_imgcodecs
    libopencv_imgproc libopencv_ml libopencv_objdetect libopencv_photo libopencv_shape libopencv_stitching libopencv_superres
    libopencv_video libopencv_videoio libopencv_videostab
                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib} )

这样配置之后，我们就可以在cpp中，直接使用OpenCV库了。在此贴一个简单的均值滤波：

#include <jni.h>
#include <string>
#include <opencv2/opencv.hpp>
#include <bits/stdc++.h>
#include <android/log.h>
#include<opencv2/core/core.hpp>
#include"opencv2/imgproc/imgproc.hpp"


using namespace cv;
using namespace std;

#define MAKE_ARGB(a, r, g, b) ((a&0xff)<<24) | ((r&0xff)<<16) | ((g&0xff)<<8) | (b&0xff)
#define MAKE_RGB565(r, g, b) ((((r) >> 3) << 11) | (((g) >> 2) << 5) | ((b) >> 3))

extern "C"
{

    JNIEXPORT jintArray JNICALL
    Java_com_live_longsiyang_opencvdemo_OpenCVNativeManager_getBlurImage(JNIEnv *env, jobject thiz,
                                                                         jintArray pixels_, jint w,
                                                                         jint h) {
        int colorType = CV_8UC4;
    
        jint *pixels = env->GetIntArrayElements(pixels_, NULL);
    
        Mat imgMat(h, w, colorType, pixels);
    
        Mat out(h, w, colorType);
    
        blur(imgMat, out, Size(20, 20));
    
        env->ReleaseIntArrayElements(pixels_, pixels, 0);
    
        int *outIntImage = new int[w * h];
    
        for (int i = 0; i < w * h; i++) {
            int a, r, g, b;
            for (int j = 0; j < 4; j++) {
                a = out.data[i * 4 + 3];
                r = out.data[i * 4 + 2];
                g = out.data[i * 4 + 1];
                b = out.data[i * 4 + 0];
                outIntImage[i] = (int) out.data[i * 4 + j];
            }
            outIntImage[i] = MAKE_ARGB(a,r,g,b);
    
        }
    
        jintArray result = env->NewIntArray(w * h);
    
        env->SetIntArrayRegion(result, 0, w * h, outIntImage);
        return result;
    
    }
}

这样我们就能看到一个基本的模糊效果的demo。

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {


    static {
        System.loadLibrary("native-lib");
    }


    ImageView mIvTest;
    Button mBtnTest;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mIvTest = (ImageView) findViewById(R.id.img_test);
        mIvTest.setImageResource(R.drawable.beauty_steward_course_video_thumb_icon);
        mBtnTest = (Button) findViewById(R.id.btn_test);
        mBtnTest.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Bitmap srcBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.beauty_steward_course_video_thumb_icon);
                int w = srcBitmap.getWidth();
                int h = srcBitmap.getHeight();
                int[] pixels = new int[w*h];
                srcBitmap.getPixels(pixels,0,w,0,0,w,h);
                int[] outPixels = OpenCVNativeManager.getBlurImage(pixels ,w,h);
                Bitmap destBitmap = Bitmap.createBitmap(w,h, Bitmap.Config.ARGB_8888);
                destBitmap.setPixels(outPixels,0,w,0,0,w,h);
                mIvTest.setImageBitmap(destBitmap);

            }
        });
        findViewById(R.id.btn_reset).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mIvTest.setImageResource(R.drawable.beauty_steward_course_video_thumb_icon);
            }
        });
    }


}

image.png

导出.so

image.png

在build中找到这个so，这就是我们需要的文件。此外，由于我们使用了opencv相关的库，我们还需要将opencv的相关文件复制出来。将其导入我们需要的工程。

image.png

导入之后，我们只需要在module的build.gradle里面加入:

android {
    ...

    sourceSets {
        main {
            jniLibs.srcDirs = ['src/main/jniLibs']
            aidl.srcDirs = ['src/main/aidl']
        }
    }
}

之后，我们就可以直接调用

System.loadLibrary("native-lib");

值得注意的是，JNI的方法是与路径名相关的，所以当我们以这样的方法调用native方法时，我们需要路径名匹配。

以上。