Android Studio + NDK JNI調用openCV圖像處理

本文介紹如何通過android studio通過jni調用openCV，不使用Opencv Manager，使用靜態編譯openCV的方式，生成單獨的一個so文件。

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

1、新建一個空的Activity工程，添加Add->Folder->JNI Folder，並添加cpp文件（Windows下再多添加一個空的，只有一個cpp文件，ndk會報錯），同樣我們使用JNI動態註冊的方式，避免較長的函數名。代碼如下：

//
// Created by user on 16-5-4.
//
#include <jni.h>
#include <android/log.h>

#include <string.h>
#include <stdio.h>
#include <android/bitmap.h>
#include <assert.h>
#include <opencv2/core/core.hpp>
#include <opencv2/core/mat.hpp>

#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>

#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

// 若這裏不加namespace cv，則下面所有openCV的數據類型都要加cv::限定
using namespace cv;

// 傳入一個bitmap對象，傳出一個包含邊緣信息的bitmap對象
// 注意前兩個參數是JNIEnv* env, jobject thiz
// JNIEnv標識當前NDK環境的對象指針,可以通過該參數訪問NDK中的內置成員，
// jobject表示調用當前NDK方法的Java對象，可以用該參數值訪問調用該方法的Java對象成員。
jobject getEdge(JNIEnv* env, jobject thiz, jobject bitmap){

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

    // 讀取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);

    // 這裏只處理RGBA_888類型的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矩陣
    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);

    // 處理求邊緣得到desMat
    Mat desMat;
    Canny(srcMat, desMat, 30.0, 90.0, 3, true);

    // 通過JAVA層的Bitmap類，新建一個bitmap對象
    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);

    // 獲取新bitmap的data數據指針
    bitmapPixels = NULL;
    if ((ret = AndroidBitmap_lockPixels(env, newBitmap, &bitmapPixels)) < 0) {
        return NULL;
    }

    // 將Mat數據寫入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函數所在的類
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、由於需要使用opencv的mk文件，這裏我們不使用Android Studio的默認ndk編譯，使用我們自己的mk文件。在jni目錄中添加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
#靜態編譯
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架構，目前有arm64-v8a，需要64位ndk以及較新的opencv
APP_ABI := armeabi, armeabi-v7a, x86 
APP_PLATFORM := android-16
APP_STL := gnustl_static

3、配置app的build.gradle，defaultConfig中添加一個編譯ndk的task，生成的so文件將會生成在src/main/jniLibs這個目錄中

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

並在在local.properties中配置好ndk路徑

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

5、新建一個java類，load lib庫，並添加native函數即可