Android Studio + NDK JNI调用openCV图像处理

本文介绍如何通过android studio通过jni调用openCV，不使用Opencv Manager，使用静态编译openCV的方式，生成单独的一个so文件。

可先看上篇文章http://blog.csdn.net/cheng20150809/article/details/51348420，AndroidStudio基本的JNI编程。

1、新建一个空的Activity工程，添加Add->Folder->JNI Folder，并添加cpp文件（Windows下再多添加一个空的，只有一个cpp文件，ndk会报错），同样我们使用JNI动态注册的方式，避免较长的函数名。代码如下：

//
// Created by user on 16-5-4.
//
#include 
#include 

#include 
#include 
#include 
#include 
#include 
#include 

#include 
#include 

#ifndef LOG
#define LOG_TAG "imgprocess"
#define ALOGD(...) \
            __android_log_print(ANDROID_LOG_DEBUG, LOG_TAG, __VA_ARGS__);
#define ALOGE(...) \
            __android_log_print(ANDROID_LOG_ERROR, LOG_TAG, __VA_ARGS__);
#define ALOGV(...) \
            __android_log_print(ANDROID_LOG_VERBOSE, LOG_TAG, __VA_ARGS__);
#endif LOG


#ifndef NELEM
# define NELEM(x) ((int) (sizeof(x) / sizeof((x)[0])))
#endif

// 若这里不加namespace cv，则下面所有openCV的数据类型都要加cv::限定
using namespace cv;

// 传入一个bitmap对象，传出一个包含边缘信息的bitmap对象
// 注意前两个参数是JNIEnv* env, jobject thiz
// JNIEnv标识当前NDK环境的对象指针,可以通过该参数访问NDK中的内置成员，
// jobject表示调用当前NDK方法的Java对象，可以用该参数值访问调用该方法的Java对象成员。
jobject getEdge(JNIEnv* env, jobject thiz, jobject bitmap){

    AndroidBitmapInfo bitmapInfo;
    uint32_t* storedBitmapPixels = NULL;
    int pixelsCount;
    int ret = -1;

    // 读取bitmap基本信息
    if ((ret = AndroidBitmap_getInfo(env, bitmap, &bitmapInfo)) < 0) {
        return NULL;
    }
    ALOGD("width:%d height:%d stride:%d", bitmapInfo.width, bitmapInfo.height, bitmapInfo.stride);

    // 这里只处理RGBA_888类型的bitmap
    if (bitmapInfo.format != ANDROID_BITMAP_FORMAT_RGBA_8888) {
        return NULL;
    }

    // 提取像素值
    void* bitmapPixels = NULL;
    if ((ret = AndroidBitmap_lockPixels(env, bitmap, &bitmapPixels)) < 0) {
        return NULL;
    }

    // 生成openCV Mat矩阵
    Mat srcMat(Size(bitmapInfo.width, bitmapInfo.height), CV_8UC4);
    pixelsCount = bitmapInfo.height * bitmapInfo.width;
    memcpy(srcMat.data, bitmapPixels, sizeof(uint32_t) * pixelsCount);
    AndroidBitmap_unlockPixels(env, bitmap);

    // 处理求边缘得到desMat
    Mat desMat;
    Canny(srcMat, desMat, 30.0, 90.0, 3, true);

    // 通过JAVA层的Bitmap类，新建一个bitmap对象
    jclass bitmapCls = env->FindClass("android/graphics/Bitmap");
    jmethodID createBitmapFunction = env->GetStaticMethodID(bitmapCls, "createBitmap", "(IILandroid/graphics/Bitmap$Config;)Landroid/graphics/Bitmap;");
    jstring configName = env->NewStringUTF("ARGB_8888");
    jclass bitmapConfigClass = env->FindClass("android/graphics/Bitmap$Config");
    jmethodID valueOfBitmapConfigFunction = env->GetStaticMethodID(bitmapConfigClass, "valueOf", "(Ljava/lang/String;)Landroid/graphics/Bitmap$Config;");
    jobject bitmapConfig = env->CallStaticObjectMethod(bitmapConfigClass, valueOfBitmapConfigFunction, configName);
    jobject newBitmap = env->CallStaticObjectMethod(bitmapCls, createBitmapFunction, desMat.cols, desMat.rows, bitmapConfig);

    // 获取新bitmap的data数据指针
    bitmapPixels = NULL;
    if ((ret = AndroidBitmap_lockPixels(env, newBitmap, &bitmapPixels)) < 0) {
        return NULL;
    }

    // 将Mat数据写入bitmap
    uint32_t* newBitmapPixels = (uint32_t*)bitmapPixels;
    pixelsCount = srcMat.cols * desMat.rows;
    for (size_t i = 0; i < pixelsCount; i++) {
        memset(&(newBitmapPixels[i]), srcMat.data[i], 3);
    }

    AndroidBitmap_unlockPixels(env, newBitmap);
    return newBitmap;
}



// native函数所在的类
static const char *classPathName = "test/hc/cvtest/MainActivity";

//
static JNINativeMethod gMethods[] = {
        {"getEdge", "(Ljava/lang/Object;)Ljava/lang/Object;", (void*)getEdge},
};

int registerNativeMethods(JNIEnv* env, const char* className,
                             JNINativeMethod* gMethods, int numMethods)
{
    jclass clazz;

    clazz = env->FindClass(className);
    if (clazz == NULL) {
        ALOGE("Native registration unable to find class '%s'", className);
        return JNI_FALSE;
    }
    if (env->RegisterNatives(clazz, gMethods, numMethods) < 0) {
        ALOGE("RegisterNatives failed for '%s'", className);
        return JNI_FALSE;
    }

    return JNI_TRUE;
}

int register_jni_methods(JNIEnv* env)
{
    return registerNativeMethods(env, classPathName, gMethods, NELEM(gMethods));
}

jint JNI_OnLoad(JavaVM* vm, void*)
{
    JNIEnv* env = NULL;
    jint result = -1;

    if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) != JNI_OK) {
        ALOGE("ERROR: GetEnv failed\n");
        goto bail;
    }
    assert(env != NULL);

    if (register_jni_methods(env) < 0) {
        ALOGE("ERROR: native registration failed\n");
        goto bail;
    }

    ALOGE("SUCCESS: native registration successed\n");
    result = JNI_VERSION_1_4;

    bail:
    return result;
}

2、由于需要使用opencv的mk文件，这里我们不使用Android Studio的默认ndk编译，使用我们自己的mk文件。在jni目录中添加Android.mk和Application.mk文件。
Android.mk

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

#opencv
OPENCVROOT:=/local/tools/OpenCV-2.4.10-android-sdk/OpenCV-2.4.10-android-sdk
OPENCV_CAMERA_MODULES:=off
OPENCV_INSTALL_MODULES:=on
#OPENCV_LIB_TYPE:=SHARED
#静态编译
OPENCV_LIB_TYPE:=STATIC
include ${OPENCVROOT}/sdk/native/jni/OpenCV.mk


LOCAL_SRC_FILES := ImgProcess.cpp
LOCAL_LDLIBS += -llog
LOCAL_LDLIBS += -ljnigraphics
LOCAL_MODULE := imgprocess

include $(BUILD_SHARED_LIBRARY)

Application.mk

# CPU架构，目前有arm64-v8a，需要64位ndk以及较新的opencv
APP_ABI := armeabi, armeabi-v7a, x86 
APP_PLATFORM := android-16
APP_STL := gnustl_static

3、配置app的build.gradle，defaultConfig中添加一个编译ndk的task，生成的so文件将会生成在src/main/jniLibs这个目录中

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.3"

    defaultConfig {
        applicationId "test.hc.cvtest"
        minSdkVersion 15
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"

        // add begin for ndk
        sourceSets.main.jni.srcDirs = []

        task ndkBuild(type: Exec, description: 'Compile JNI source via NDK') {
            commandLine "$ndkDir/ndk-build",
                    'NDK_PROJECT_PATH=build/intermediates/ndk',
                    'NDK_LIBS_OUT=src/main/jniLibs',
                    'APP_BUILD_SCRIPT=src/main/jni/Android.mk',
                    'NDK_APPLICATION_MK=src/main/jni/Application.mk'
        }

        tasks.withType(JavaCompile) {
            compileTask -> compileTask.dependsOn ndkBuild
        }
        // add end for ndk
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

4、在gradle.properties中添加：

android.useDeprecatedNdk=true
ndkDir=/local/tools/android-ndk-r10

并在在local.properties中配置好ndk路径

ndk.dir=/local/tools/android-ndk-r10

5、新建一个java类，load lib库，并添加native函数即可