前言
以前的文章中《OpenCV简介与Android SDK环境》列出过OpenCV4Android的开发，不过当时是用的Java实现，做了一些Demo后慢慢发现，在图像处理中用JAVA调OpenCV的开发处理速度是个瓶颈，所以才激起了学习NDK开发的想法，具体NDK开发的配置可以看我前面的文章《Android NDK编程（一）---NDK介绍及环境搭建》，本章主要说后面的OpenCV在Android NDK开发的环境搭建。
准备工作
开发环境
- Android Studio 3.3.2
- NDK 19.2.5345600
- OpenCV for Android 4.1.0
NDK的搭建
详见《Android NDK编程（一）---NDK介绍及环境搭建》
OpenCV下载及准备
下载地址：https://opencv.org/releases/
找到最新版本4.1.0的下载地址，点击Android进入下载
下载完后就是我们下图红框中的ZIP文件，然后我们解压一下后即生成了OpenCV-android-sdk的文件夹（下图蓝框）
OpenCV4Android项目配置
1.创建项目
我们打开Android Studio新建一个项目，选择Native C
将程序名称改为OpenCVDemo
C Stand选择为C 11
点击Finish后我们完成了项目的创建
2.修改build.gradle文件
双击build.gradle文件
修改要我们要支持的CPU架构下
调用OpenCV4Android中的so动态库用于打包进APK，下图中红框内的路径就是我们上面下载的OpenCV4.1.0中的动态库路径
我们看一下那个路径
完整的build.gradle代码
代码语言：javascript复制apply plugin: 'com.android.application'
android {
compileSdkVersion 28
defaultConfig {
applicationId "dem.vac.opencvdemo"
minSdkVersion 14
targetSdkVersion 28
versionCode 1
versionName "1.0"
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
externalNativeBuild {
cmake {
cppFlags "-std=c 11"
//我们的APP要支持的CPU架构
abiFilters'x86','armeabi-v7a'
}
}
}
//加上
sourceSets{
main{
//当前这个目录下的库文件会被调用并且被打包进apk中
jniLibs.srcDirs = ['D:/PersonalStudio/OpenCV-android-sdk/sdk/native/libs']
}
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
}
}
externalNativeBuild {
cmake {
path "src/main/cpp/CMakeLists.txt"
}
}
}
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'com.android.support:appcompat-v7:28.0.0'
implementation 'com.android.support.constraint:constraint-layout:1.1.3'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:1.0.2'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
}
3.修改CMakeLists.txt文件
下图中标红框的地方就是我在原来的CMakeLists.txt中修改的地方
完整的CMakeList.txt代码
代码语言：javascript复制# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html
# Sets the minimum version of CMake required to build the native library.
cmake_minimum_required(VERSION 3.4.1)
#该变量为真时会创建完整版本的Makefile
set(CMAKE_VERBOSE_MAKEFILE on)
#定义变量ocvlibs使后面的命令可以使用定位具体的库文件
set(opencvlibs "D:/PersonalStudio/OpenCV-android-sdk/sdk/native/libs")
#调用头文件的具体路径
include_directories(D:/PersonalStudio/OpenCV-android-sdk/sdk/native/jni/include)
#增加我们的动态库
add_library(libopencv_java4 SHARED IMPORTED)
#建立链接
set_target_properties(libopencv_java4 PROPERTIES IMPORTED_LOCATION
"${opencvlibs}/${ANDROID_ABI}/libopencv_java4.so")
# 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.
add_library( # Sets the name of the library.
native-lib
# Sets the library as a shared library.
SHARED
# Provides a relative path to your source file(s).
native-lib.cpp)
# 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.
native-lib libopencv_java4
# Links the target library to the log library
# included in the NDK.
${log-lib})划重点
修改完后我们需要点击选项上的Build-Refresh Linked C Projects
完成后我们展开native-lib下面的includes后里面有个opencv2已经添加进来了，如下图：
上面我们的Android Studio通过NDK配置OpenCV已经完下了，下面开始我就可以进行代码的编写了。
-END-
