NDK和JNI

JNI是Java Native Interface（JAVA本地接口）的縮寫(xiě)，為了方便Java調(diào)用C林艘、C++等本地代碼所封裝的一層接口混坞。Java的跨平臺(tái)特性導(dǎo)致了其本地交互能力的不足究孕，一些和操作系統(tǒng)相關(guān)的特性java無(wú)法完成。
NDK是Android所提供的一個(gè)工具集合厨诸，通過(guò)NDK可以在Android中更加方便的通過(guò)JNI來(lái)訪問(wèn)本地代碼泳猬。
總之，JNI是一個(gè)協(xié)議埋心，NDK是服務(wù)JNI的工具忙上。

在C:\Users\用戶\AppData\Local\Android\Sdk\ndk-bundle目錄下存放著ndk的信息，其中arm64就是我們平時(shí)用的手機(jī)的硬件架構(gòu)茬斧。

ndk platforms.png

toolchains用于不同平臺(tái)交叉編譯项秉，也是經(jīng)常會(huì)報(bào)錯(cuò)的地方。

ndk toolchains 不同平臺(tái)交叉編譯.png

主要構(gòu)成

涉及到C++與Kotlin之間的銜接的部分目錄有：
gradle： \MagicCamera3\app\build.gradle
cmake： \MagicCamera3\app\CMakeLists.txt
cpp代碼： \MagicCamera3\app\src\main\cpp\magicjni.cpp主函數(shù)
kotlin部分代碼: \MagicCamera3\app\src\main\java\com\cangwang\magic\util\OpenGLJniLib.kt

從Cmake函數(shù)入手怖喻，CMake工具輔助我們結(jié)局C++代碼的依賴關(guān)系锚沸，先指向用到的cpp代碼src/main/cpp/magicjni.cpp等涕癣，再設(shè)置到依賴，包括：magicjni恬叹、android同眯、GLESv3、EGL和log-lib硅确。

# 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.

include_directories(${CMAKE_SOURCE_DIR} src/main/cpp)

add_library( # Sets the name of the library.
             magicjni

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
        src/main/cpp/magicjni.cpp
        # 省略若干行菱农。柿估。。的妖。)

# 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.
                       magicjni
                       android
                       GLESv3
                       EGL

                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib} )

在項(xiàng)目app的gradle build中：

android {
    defaultConfig {
        applicationId "com.cangwang.magic"
        // ......
        externalNativeBuild {
            cmake {
                cppFlags "-std=c++11 -fexceptions"
            }
        }
        ndk {
            abiFilters "armeabi-v7a"
        }
    }
    externalNativeBuild {
        cmake {
            path "CMakeLists.txt"
        }
    }
}

其中：armeabi就是針對(duì)普通的或舊的arm cpu嫂粟，armeabi-v7a是針對(duì)有浮點(diǎn)運(yùn)算或高級(jí)擴(kuò)展功能的arm cpu墨缘。gradle中定位了CMake的位置。

最后就是kotlin和C++代碼的一一對(duì)應(yīng)關(guān)系
先看kotlin代碼：

package com.cangwang.magic.util

import android.content.res.AssetManager
import android.view.Surface

/**
 * openGL輔助類(lèi)
 * Created by cangwang on 2018/10/12.
 */
object OpenGLJniLib{
    init {
        System.loadLibrary("magicjni")
    }

    /**
     * 初始化magicBaseView
     */
    external fun magicBaseInit(surface:Surface, width:Int, height:Int, manager: AssetManager):Int

    /**
     * 創(chuàng)建magicBaseView
     */
    external fun magicBaseCreate()

    /**
     * 變更觸發(fā)magicBaseView
     */
    external fun magicBaseChange(width:Int,height:Int)

    /**
     * 繪制
     */
    external fun magicBaseDraw(matrix:FloatArray)

    external fun magicBaseRelease()

    /**
     * 調(diào)整大小
     */
    external fun magicAdjustSize(orientation:Int,isFront:Boolean,flipVertical:Boolean)


    /**
     * 相機(jī)濾鏡創(chuàng)建
     */
    external fun magicFilterCreate(surface:Surface,manager: AssetManager):Int

    external fun magicFilterChange(width:Int,height:Int)

    external fun magicFilterDraw(matrix:FloatArray,isTakePhoto:String)

    external fun magicFilterRelease()


    /**
     * 圖片濾鏡創(chuàng)建
     */
    external fun magicImageFilterCreate(surface:Surface,manager: AssetManager,path:String,degree:Int):Int

    external fun magicImageFilterChange(width:Int,height:Int)

    external fun magicImageFilterDraw(matrix:FloatArray,isSavePhoto:String)

    external fun magicImageFilterRelease()

    /**
     * 設(shè)置美顏級(jí)別
     */
    external fun setImageBeautyLevel(level:Int)


    /**
     * 獲取濾鏡列表
     */
    external fun getFilterTypes():IntArray

    /**
     * 設(shè)置濾鏡類(lèi)型
     */
    external fun setFilterType(type:Int)

    external fun setImageFilterType(type:Int)

    /**
     * 設(shè)置美顏級(jí)別
     */
    external fun setBeautyLevel(level:Int)

    /**
     * 攝像頭保存圖片
     */
    external fun savePhoto(address:String):Boolean

    /**
     * 編輯保存圖片
     */
    external fun saveImage(address: String):Boolean
}

再看Cpp代碼main方法：

#include <jni.h>
#include <android/log.h>
#include <android/asset_manager.h>
#include <android/asset_manager_jni.h>
#include <android/native_window_jni.h>
#include <mutex>
#include <thread>
#include <stdio.h>
#include <malloc.h>
#include <GLES3/gl3.h>
#include <src/main/cpp/filter/MagicFilterFactory.h>
#include <src/main/cpp/image/ImageFilter.h>
#include "src/main/cpp/camera/CameraEngine.h"
#include "src/main/cpp/camera/CameraFilter.h"

#define LOG_TAG "magicjni"
#define ALOGE(...) __android_log_print(ANDROID_LOG_ERROR, LOG_TAG, __VA_ARGS__)
#define ALOGV(...) __android_log_print(ANDROID_LOG_VERBOSE, LOG_TAG, __VA_ARGS__)
extern "C" {

    std::mutex gMutex;
    CameraEngine *glCamera = nullptr;
    CameraFilter *glCameraFilter = nullptr;
    ImageFilter *glImageFilter = nullptr;
    AAssetManager *aAssetManager = nullptr;

    JNIEXPORT jint JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_magicBaseInit(JNIEnv *env, jobject obj,
                                                            jobject surface,jint width,jint height,jobject assetManager) {}


    JNIEXPORT void JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_magicBaseCreate(JNIEnv *env, jobject obj) {}

    JNIEXPORT void JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_magicBaseChange(JNIEnv *env, jobject obj,jint width,jint height) {}

    JNIEXPORT void JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_magicBaseDraw(JNIEnv *env, jobject obj,jfloatArray matrix_) {}

    JNIEXPORT void JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_magicBaseRelease(JNIEnv *env, jobject obj) {}

    JNIEXPORT void JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_magicAdjustSize(JNIEnv *env, jobject obj,jint orientation,jboolean isFront,jboolean flipVertical) {}

    //相機(jī)濾鏡surfaceView初始化的時(shí)候創(chuàng)建
    JNIEXPORT jint JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_magicFilterCreate(JNIEnv *env, jobject obj,
                                                            jobject surface,jobject assetManager) {}

    JNIEXPORT void JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_magicFilterSet(JNIEnv *env, jobject obj,
                                                                jobject surface,jobject assetManager) {}

    //窗口大小設(shè)置卸亮，SurfaceView初始化后會(huì)觸發(fā)一次
    JNIEXPORT void JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_magicFilterChange(JNIEnv *env, jobject obj,jint width,jint height) {}

    JNIEXPORT void JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_magicFilterDraw(JNIEnv *env, jobject obj,jfloatArray matrix_,jstring address) {}

    JNIEXPORT void JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_magicFilterRelease(JNIEnv *env, jobject obj) {}

    //圖片濾鏡surfaceView初始化的時(shí)候創(chuàng)建
    JNIEXPORT jint JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_magicImageFilterCreate(JNIEnv *env, jobject obj,
                                                                jobject surface,jobject assetManager,jstring imgPath,jint degree) {}

    //窗口大小設(shè)置嫡良，SurfaceView初始化后會(huì)觸發(fā)一次
    JNIEXPORT void JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_magicImageFilterChange(JNIEnv *env, jobject obj,jint width,jint height) {}

    JNIEXPORT void JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_magicImageFilterDraw(JNIEnv *env, jobject obj,jfloatArray matrix_,jstring address) {}

    JNIEXPORT void JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_magicImageFilterRelease(JNIEnv *env, jobject obj) {}


    JNIEXPORT jintArray JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_getFilterTypes(JNIEnv *env, jobject obj) {}

    JNIEXPORT void JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_setFilterType(JNIEnv *env, jobject obj,jint type) {}

    JNIEXPORT void JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_setImageFilterType(JNIEnv *env, jobject obj,jint type) {}

    JNIEXPORT void JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_setImageBeautyLevel(JNIEnv *env, jobject obj,jint level) {}


    JNIEXPORT void JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_setBeautyLevel(JNIEnv *env, jobject obj,jint level) {}

    JNIEXPORT jboolean JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_savePhoto(JNIEnv *env, jobject obj,jstring address) {}

    JNIEXPORT jboolean JNICALL
    Java_com_cangwang_magic_util_OpenGLJniLib_saveImage(JNIEnv *env, jobject obj,jstring address) {}

}

關(guān)聯(lián)Cpp的函數(shù)命名需要注意寝受，規(guī)則是：Java_全類(lèi)名_方法名罕偎。