基于Android studio3.6的JNI教程之opencv实例详解

2023-07-28 16:00:14 53

基本环境：

Androidstudio3.6

NDK:r14b（尽量使用该版本）

Opencv3.4.1androidsdk

(1)新建工程OpenCVDemo，选择，一定要选择Nativec++类型，最后要选c++14支持。

(2)File->ProjectStructure->SDKLocation,设置这3个路径，NDK选择r14b。

(3)任意找一张图片，复制到res/drawable。

(4)修改布局文件res/layout/activity_main.xml

(5)修改java文件，app/src/main/java/com.example.opencvdemo/MainActivity

主要修改包括修改

继承OnClickListener类，

修改onCreate方法

增加c++的接口函数，getEdge

实现点击按钮的方法，

整体代码如下，

(6)Termi

packagecom.example.opencvdemo;
importandroidx.appcompat.app.AppCompatActivity;
importandroid.graphics.Bitmap;
importandroid.graphics.BitmapFactory;
importandroid.os.Bundle;
importandroid.view.View;
importandroid.widget.ImageView;
importandroid.widget.TextView;
publicclassMainActivityextendsAppCompatActivityimplementsView.OnClickListener{
//Usedtoloadthe'native-lib'libraryonapplicationstartup.
static{
System.loadLibrary("native-lib");
}
@Override
protectedvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
imageView=findViewById(R.id.imageView);
findViewById(R.id.show).setOnClickListener(this);
findViewById(R.id.process).setOnClickListener(this);
}
/**
*Anativemethodthatisimplementedbythe'native-lib'nativelibrary,
*whichispackagedwiththisapplication.
*/
//获得Canny边缘
publicnativevoidgetEdge(Objectbitmap);
privateImageViewimageView;
@Override
publicvoidonClick(Viewv){
if(v.getId()==R.id.show){
Bitmapbitmap=BitmapFactory.decodeResource(getResources(),R.drawable.test);
imageView.setImageBitmap(bitmap);
}else{
Bitmapbitmap=BitmapFactory.decodeResource(getResources(),R.drawable.test);
getEdge(bitmap);
imageView.setImageBitmap(bitmap);
}
}
}

nal下进入app\src\main\java这一层目录，执行，

javahcom.example.opencvdemo.MainActivity

将生成的com_example_opencvdemo_MainActivity.h，剪切到app/src/main/cpp目录下。

(7)修改app/src/main/cpp下面的native-lib.cpp，主要通过c++实现getEdge方法，主要代码如下，

#include
#include
#include"com_example_opencvdemo_MainActivity.h"
#include
#include
usingnamespacecv;
extern"C"
JNIEXPORTvoidJNICALL
Java_com_example_opencvdemo_MainActivity_getEdge(JNIEnv*env,jobjectobj,jobjectbitmap){
//TODO:implementgetEdge()
AndroidBitmapInfoinfo;
void*pixels;
CV_Assert(AndroidBitmap_getInfo(env,bitmap,&info)>=0);
CV_Assert(info.format==ANDROID_BITMAP_FORMAT_RGBA_8888||
info.format==ANDROID_BITMAP_FORMAT_RGB_565);
CV_Assert(AndroidBitmap_lockPixels(env,bitmap,&pixels)>=0);
CV_Assert(pixels);
if(info.format==ANDROID_BITMAP_FORMAT_RGBA_8888){
Mattemp(info.height,info.width,CV_8UC4,pixels);
Matgray;
cvtColor(temp,gray,COLOR_RGBA2GRAY);
Canny(gray,gray,125,225);
cvtColor(gray,temp,COLOR_GRAY2RGBA);
}else{
Mattemp(info.height,info.width,CV_8UC2,pixels);
Matgray;
cvtColor(temp,gray,COLOR_RGB2GRAY);
Canny(gray,gray,125,225);
cvtColor(gray,temp,COLOR_GRAY2RGB);
}
AndroidBitmap_unlockPixels(env,bitmap);
}

(8)修改CMakeLists.txt

包括增加opencv包含路径，增加opencv链接，增加目标库的链接（OpenCV_LIBS和jnigraphics）

全部代码如下，

#FormoreinformationaboutusingCMakewithAndroidStudio,readthe
#documentation:https://d.android.com/studio/projects/add-native-code.html
#SetstheminimumversionofCMakerequiredtobuildthenativelibrary.
cmake_minimum_required(VERSION3.4.1)
#Createsandnamesalibrary,setsitaseitherSTATIC
#orSHARED,andprovidestherelativepathstoitssourcecode.
#Youcandefinemultiplelibraries,andCMakebuildsthemforyou.
#GradleautomaticallypackagessharedlibrarieswithyourAPK.
#设置OpenCV-android-sdk路径
set(OpenCV_DIRE:/Android/OpenCV-android-sdk/sdk/native/jni)
find_package(OpenCVREQUIRED)
if(OpenCV_FOUND)
include_directories(${OpenCV_INCLUDE_DIRS})
message(STATUS"OpenCVlibrarystatus:")
message(STATUS"version:${OpenCV_VERSION}")
message(STATUS"libraries:${OpenCV_LIBS}")
message(STATUS"includepath:${OpenCV_INCLUDE_DIRS}")
else(OpenCV_FOUND)
message(FATAL_ERROR"OpenCVlibrarynotfound")
endif(OpenCV_FOUND)

set(CMAKE_SHARED_LINKER_FLAGS"${CMAKE_SHARED_LINKER_FLAGS}-Wl,--exclude-libs,libippicv.a-Wl,--exclude-libs,libippiw.a")

add_library(#Setsthenameofthelibrary.
native-lib

#Setsthelibraryasasharedlibrary.
SHARED

#Providesarelativepathtoyoursourcefile(s).
native-lib.cpp)

#Searchesforaspecifiedprebuiltlibraryandstoresthepathasa
#variable.BecauseCMakeincludessystemlibrariesinthesearchpathby
#default,youonlyneedtospecifythenameofthepublicNDKlibrary
#youwanttoadd.CMakeverifiesthatthelibraryexistsbefore
#completingitsbuild.

find_library(#Setsthenameofthepathvariable.
log-lib

#SpecifiesthenameoftheNDKlibrarythat
#youwantCMaketolocate.
log)

#SpecifieslibrariesCMakeshouldlinktoyourtargetlibrary.You
#canlinkmultiplelibraries,suchaslibrariesyoudefineinthis
#buildscript,prebuiltthird-partylibraries,orsystemlibraries.

target_link_libraries(#Specifiesthetargetlibrary.
native-lib
${OpenCV_LIBS}
jnigraphics
#Linksthetargetlibrarytotheloglibrary
#includedintheNDK.
${log-lib})

(9)修改app/build.gradle

主要增加cmake的cppFlags，arguments

全部代码如下，

applyplugin:'com.android.application'
android{
compileSdkVersion29
buildToolsVersion"29.0.3"
defaultConfig{
applicationId"com.example.opencvdemo"
minSdkVersion16
targetSdkVersion29
versionCode1
versionName"1.0"
testInstrumentationRunner"androidx.test.runner.AndroidJUnitRunner"
externalNativeBuild{
cmake{
cppFlags"-std=c++14-frtti-fexceptions"
arguments'-DANDROID_STL=gnustl_shared'//支持C++异常处理标准模板快,ndk16+需要注释
//abiFilters"armeabi-v7a","arm64-v8a","x86_64"
}
}
}
buildTypes{
release{
minifyEnabledfalse
proguardFilesgetDefaultProguardFile('proguard-android-optimize.txt'),'proguard-rules.pro'
}
}
externalNativeBuild{
cmake{
path"src/main/cpp/CMakeLists.txt"
version"3.10.2"
}
}
}
dependencies{
implementationfileTree(dir:'libs',include:['*.jar'])
implementation'androidx.appcompat:appcompat:1.1.0'
implementation'androidx.constraintlayout:constraintlayout:1.1.3'
testImplementation'junit:junit:4.12'
androidTestImplementation'androidx.test.ext:junit:1.1.1'
androidTestImplementation'androidx.test.espresso:espresso-core:3.2.0'
}

(10)整体目录结构如下，

运行程序，

代码链接：

References:

https://www.jianshu.com/p/6e16c0429044

https://www.bilibili.com/video/av55834524/

总结

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基于Android studio3.6的JNI教程之opencv实例详解

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