Android Studio 通过NDK调用OpenCV

所用as版本为2.0 ndk版本为r10d 安卓版本为5.0 系统为win10 opencv版本为3.1

首先新建一个工程

然后将sdk目录下的native文件夹复制过来

然后在app/src/main文件夹下新建一个文件夹 叫做jni 再在这个文件夹里新建两个文件 Application.mk Android.mk

接着修改一下gradle.properties文件和local.properties文件

gradle.properties内添加

android.useDeprecatedNdk=true

local.properties内添加ndk的路径

然后修改build.gradle，在android下添加

sourceSets.main.jni.srcDirs = []
    //禁止自带的ndk功能
    sourceSets.main.jniLibs.srcDirs = ['src/main/libs','src/main/jniLibs']
    //重定向so目录为src/main/libs和src/main/jniLibs，原来为src/main/jniLibs

    task ndkBuild(type: Exec, description: 'Compile JNI source with NDK') {
        Properties properties = new Properties()
        properties.load(project.rootProject.file('local.properties').newDataInputStream())
        def ndkDir = properties.getProperty('ndk.dir')

        if (org.apache.tools.ant.taskdefs.condition.Os.isFamily(org.apache.tools.ant.taskdefs.condition.Os.FAMILY_WINDOWS)) {
            commandLine "$ndkDir/ndk-build.cmd", '-C', file('src/main/jni').absolutePath
        } else {
            commandLine "$ndkDir/ndk-build", '-C', file('src/main/jni').absolutePath
        }
    }

    tasks.withType(JavaCompile) {
        compileTask -> compileTask.dependsOn ndkBuild
    }

    task ndkClean(type: Exec, description: 'Clean NDK Binaries') {
        Properties properties = new Properties()
        properties.load(project.rootProject.file('local.properties').newDataInputStream())
        def ndkDir = properties.getProperty('ndk.dir')

        if (org.apache.tools.ant.taskdefs.condition.Os.isFamily(org.apache.tools.ant.taskdefs.condition.Os.FAMILY_WINDOWS)) {
            commandLine "$ndkDir/ndk-build.cmd",'clean', '-C', file('src/main/jni').absolutePath
        } else {
            commandLine "$ndkDir/ndk-build",'clean', '-C', file('src/main/jni').absolutePath
        }
    }

    clean.dependsOn 'ndkClean'

修改完后如下

apply plugin: 'com.android.application'

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.3"

    defaultConfig {
        applicationId "com.example.chengk.opencvndk"
        minSdkVersion 21
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }


    sourceSets.main.jni.srcDirs = []
    //禁止自带的ndk功能
    sourceSets.main.jniLibs.srcDirs = ['src/main/libs','src/main/jniLibs']
    //重定向so目录为src/main/libs和src/main/jniLibs，原来为src/main/jniLibs

    task ndkBuild(type: Exec, description: 'Compile JNI source with NDK') {
        Properties properties = new Properties()
        properties.load(project.rootProject.file('local.properties').newDataInputStream())
        def ndkDir = properties.getProperty('ndk.dir')

        if (org.apache.tools.ant.taskdefs.condition.Os.isFamily(org.apache.tools.ant.taskdefs.condition.Os.FAMILY_WINDOWS)) {
            commandLine "$ndkDir/ndk-build.cmd", '-C', file('src/main/jni').absolutePath
        } else {
            commandLine "$ndkDir/ndk-build", '-C', file('src/main/jni').absolutePath
        }
    }

    tasks.withType(JavaCompile) {
        compileTask -> compileTask.dependsOn ndkBuild
    }

    task ndkClean(type: Exec, description: 'Clean NDK Binaries') {
        Properties properties = new Properties()
        properties.load(project.rootProject.file('local.properties').newDataInputStream())
        def ndkDir = properties.getProperty('ndk.dir')

        if (org.apache.tools.ant.taskdefs.condition.Os.isFamily(org.apache.tools.ant.taskdefs.condition.Os.FAMILY_WINDOWS)) {
            commandLine "$ndkDir/ndk-build.cmd",'clean', '-C', file('src/main/jni').absolutePath
        } else {
            commandLine "$ndkDir/ndk-build",'clean', '-C', file('src/main/jni').absolutePath
        }
    }

    clean.dependsOn 'ndkClean'
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    compile 'com.android.support:appcompat-v7:23.3.0'
}

接着创建一个java类，我这的为OPenCVCPP

代码为

package com.example.chengk.opencvndk;

/**
 * Created by chengk on 2016/5/25.
 */
public class OpenCVCPP {
    static {
        System.loadLibrary("OpenCV");
    }
    public static native int[] gray(int[] buf, int w, int h);
}

然后使用javah创建一个头文件 使用刚才创建的那个java类

我这里需要转到classes下的debug文件夹才能成功创建

javah -classpath . -jni com.example.chengk.opencvndk.OpenCVCPP

创建好后把那个文件复制到jni文件夹中
再在jni文件夹中创建一个cpp文件

代码为

//
// Created by chengk on 2016/5/25.
//

#include "com_example_chengk_opencvndk_OpenCVCPP.h"
#include 
#include 
#include 

using namespace cv;

extern "C" {

JNIEXPORT jintArray JNICALL Java_com_example_chengk_opencvndk_OpenCVCPP_gray(
        JNIEnv *env, jclass obj, jintArray buf, int w, int h);



JNIEXPORT jintArray JNICALL Java_com_example_chengk_opencvndk_OpenCVCPP_gray(
        JNIEnv *env, jclass obj, jintArray buf, int w, int h) {

    jint *cbuf;
    cbuf = env->GetIntArrayElements(buf, JNI_FALSE );
    if (cbuf == NULL) {
        return 0;
    }

    Mat imgData(h, w, CV_8UC4, (unsigned char *) cbuf);

    uchar* ptr = imgData.ptr(0);
    for(int i = 0; i < w*h; i ++){
        //计算公式：Y(亮度) = 0.299*R + 0.587*G + 0.114*B
        //对于一个int四字节，其彩色值存储方式为：BGRA
        int grayScale = (int)(ptr[4*i+2]*0.299 + ptr[4*i+1]*0.587 + ptr[4*i+0]*0.114);
        ptr[4*i+1] = grayScale;
        ptr[4*i+2] = grayScale;
        ptr[4*i+0] = grayScale;
    }

    int size = w * h;
    jintArray result = env->NewIntArray(size);
    env->SetIntArrayRegion(result, 0, size, cbuf);
    env->ReleaseIntArrayElements(buf, cbuf, 0);
    return result;
}
}

接着在Android.mk中添加

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)


OpenCV_INSTALL_MODULES := on
OpenCV_CAMERA_MODULES := off

OPENCV_LIB_TYPE :=STATIC

ifeq ("$(wildcard $(OPENCV_MK_PATH))","")
include ..\..\..\..\native\jni\OpenCV.mk
else
include $(OPENCV_MK_PATH)
endif

LOCAL_MODULE := OpenCV

LOCAL_SRC_FILES :=

LOCAL_LDLIBS +=  -lm -llog
LOCAL_SRC_FILES := com_example_chengk_opencvndk_OpenCVCPP.cpp

include $(BUILD_SHARED_LIBRARY)

倒数第二行是所需编译的cpp文件名

在Application.mk中添加

APP_STL := gnustl_static
APP_CPPFLAGS := -frtti -fexceptions
APP_ABI := armeabi armeabi-v7a x86
APP_PLATFORM := android-8

接着使用gradle构建一下

成功的话会看到这个

用来测试的代码

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Bitmap bitmap = ((BitmapDrawable) getResources().getDrawable(
                R.drawable.aaa)).getBitmap();
        int w = bitmap.getWidth(), h = bitmap.getHeight();
        int[] pix = new int[w * h];
        bitmap.getPixels(pix, 0, w, 0, 0, w, h);
        int [] resultPixes=OpenCVCPP.gray(pix,w,h);
        Bitmap result = Bitmap.createBitmap(w,h, Bitmap.Config.RGB_565);
        result.setPixels(resultPixes, 0, w, 0, 0,w, h);
        ImageView img=(ImageView)findViewById(R.id.imageView);
        img.setImageBitmap((result));
    }
}

测试用图片

运行结果

这样做安装包的体积还可以 不算上x86的支持的话不到10M