NDK和JNI
JNI是Java Native Interface（JAVA本地接口）的缩写，为了方便Java调用C、C++等本地代码所封装的一层接口。Java的跨平台特性导致了其本地交互能力的不足，一些和操作系统相关的特性java无法完成。
NDK是Android所提供的一个工具集合，通过NDK可以在Android中更加方便的通过JNI来访问本地代码。
总之，JNI是一个协议，NDK是服务JNI的工具。
在C:\Users\用户\AppData\Local\Android\Sdk\ndk-bundle目录下存放着ndk的信息，其中arm64就是我们平时用的手机的硬件架构。
ndk platforms.png
toolchains用于不同平台交叉编译，也是经常会报错的地方。
ndk toolchains 不同平台交叉编译.png
主要构成
涉及到C++与Kotlin之间的衔接的部分目录有：
gradle： \MagicCamera3\app\build.gradle
cmake： \MagicCamera3\app\CMakeLists.txt
cpp代码： \MagicCamera3\app\src\main\cpp\magicjni.cpp主函数
kotlin部分代码: \MagicCamera3\app\src\main\java\com\cangwang\magic\util\OpenGLJniLib.kt
从Cmake函数入手，CMake工具辅助我们结局C++代码的依赖关系，先指向用到的cpp代码src/main/cpp/magicjni.cpp等，再设置到依赖，包括：magicjni、android、GLESv3、EGL和log-lib。
# 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。。。。)
# 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} )
在项目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就是针对普通的或旧的arm cpu，armeabi-v7a是针对有浮点运算或高级扩展功能的arm cpu。gradle中定位了CMake的位置。
最后就是kotlin和C++代码的一一对应关系
先看kotlin代码：
package com.cangwang.magic.util
import android.content.res.AssetManager
import android.view.Surface
/**
* openGL辅助类
* 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
/**
* 创建magicBaseView
*/
external fun magicBaseCreate()
/**
* 变更触发magicBaseView
*/
external fun magicBaseChange(width:Int,height:Int)
/**
* 绘制
*/
external fun magicBaseDraw(matrix:FloatArray)
external fun magicBaseRelease()
/**
* 调整大小
*/
external fun magicAdjustSize(orientation:Int,isFront:Boolean,flipVertical:Boolean)
/**
* 相机滤镜创建
*/
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()
/**
* 图片滤镜创建
*/
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()
/**
* 设置美颜级别
*/
external fun setImageBeautyLevel(level:Int)
/**
* 获取滤镜列表
*/
external fun getFilterTypes():IntArray
/**
* 设置滤镜类型
*/
external fun setFilterType(type:Int)
external fun setImageFilterType(type:Int)
/**
* 设置美颜级别
*/
external fun setBeautyLevel(level:Int)
/**
* 摄像头保存图片
*/
external fun savePhoto(address:String):Boolean
/**
* 编辑保存图片
*/
external fun saveImage(address: String):Boolean
}
再看Cpp代码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) {}
//相机滤镜surfaceView初始化的时候创建
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) {}
//窗口大小设置，SurfaceView初始化后会触发一次
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) {}
//图片滤镜surfaceView初始化的时候创建
JNIEXPORT jint JNICALL
Java_com_cangwang_magic_util_OpenGLJniLib_magicImageFilterCreate(JNIEnv *env, jobject obj,
jobject surface,jobject assetManager,jstring imgPath,jint degree) {}
//窗口大小设置，SurfaceView初始化后会触发一次
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) {}
}
关联Cpp的函数命名需要注意，规则是：Java_全类名_方法名。
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