Android如何通过cmake的方式接入opencv

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简述

上篇我们通过Java sdk的方式已经将opencv接入到项目中了，如果想使用opencv sdk 提供的 C++ 头文件与 .so动态库,自己封装jni这样使用上篇的方式显然是不能实现的。所以本篇我们介绍通过cmake的方式接入opencv。

接入步骤

1、新建jni项目

Android如何通过cmake的方式接入opencv

具体创建过程参考上篇：通过Java sdk方式接入opencv 。

2、导入so库

在项目app/src/main目录下新建jniLibs，并将解压后的opencv sdk 目录下对应的路径 sdk/native/libs 中的文件复制到jniLibs中。

Android如何通过cmake的方式接入opencv

2、导入cpp文件

将opencv sdk 目录下对应的路径 sdk/native/jni/include 中的文件复制到cpp目录中。

Android如何通过cmake的方式接入opencv

3、修改CMakeLists

将src/main/cpp 中的CMakeLists移动到app目录下。

Android如何通过cmake的方式接入opencv

2.修改CMakeLists中的内容

# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html
# 设置CMAKE的版本号
cmake_minimum_required(VERSION 3.4.1)

# 设置include文件夹的地址
include_directories(${CMAKE_SOURCE_DIR}/src/main/cpp/include)

# 设置opencv的动态库
add_library(libopencv_java4 SHARED IMPORTED)
set_target_properties(libopencv_java4 PROPERTIES IMPORTED_LOCATION
    ${CMAKE_SOURCE_DIR}/src/main/jniLibs/${ANDROID_ABI}/libopencv_java4.so)

add_library( # Sets the name of the library.
    native-lib #.so库名 可自定义

    # Sets the library as a shared library.
    SHARED

    # Provides a relative path to your source file(s).
    src/main/cpp/native-lib.cpp)

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)

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})

修改app 中的build.gradle文件 defaultConfig 中配置cmake和ndk

externalNativeBuild {
    cmake {
      cppFlags "-std=c++11"
      arguments "-DANDROID_STL=c++_shared"
    }
}
ndk{
   abiFilters "armeabi-v7a","arm64-v8a"
}

android 中配置jniLibs

sourceSets{
   main{
     jniLibs.srcDirs = ['src/main/jniLibs']
   }
}

android 中配置cmake和ndk相关

externalNativeBuild {
    cmake {
      path file('CMakeLists.txt')
      version "3.10.2"
    }
  }

splits {
  abi {
    enable true
    reset()
    include 'x86', 'x86_64', 'armeabi-v7a', 'arm64-v8a' //select ABIs to build APKs for
    universalApk true //generate an additional APK that contains all the ABIs
  }
}

如果是老项目则不必配置splits否则会报错，只需要干掉下面的代码

splits {
  abi {
    enable true
    reset()
    include 'x86', 'x86_64', 'armeabi-v7a', 'arm64-v8a' //select ABIs to build APKs for
    universalApk true //generate an additional APK that contains all the ABIs
  }
}

最终配置完的代码为：

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'

android {
  compileSdkVersion 29

  defaultConfig {
    applicationId "com.jd.opencv"
    minSdkVersion 23
    targetSdkVersion 29
    versionCode 1
    versionName "1.0"

    testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"

    externalNativeBuild {
      cmake {
        cppFlags "-std=c++11"
        arguments "-DANDROID_STL=c++_shared"
      }
    }
    ndk{
      abiFilters "armeabi-v7a","arm64-v8a"
    }
  }

  sourceSets{
    main{
      jniLibs.srcDirs = ['src/main/jniLibs']
    }
  }

  buildTypes {
    release {
      minifyEnabled false
      proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
    }
  }

  externalNativeBuild {
    cmake {
      path file('CMakeLists.txt')
      version "3.10.2"
    }
  }

  splits {
    abi {
      enable true
      reset()
      include 'x86', 'x86_64', 'armeabi-v7a', 'arm64-v8a' //select ABIs to build APKs for
      universalApk true //generate an additional APK that contains all the ABIs
    }
  }

  project.ext.versionCodes = ['armeabi': 1, 'armeabi-v7a': 2, 'arm64-v8a': 3, 'mips': 5, 'mips64': 6, 'x86': 8, 'x86_64': 9]

  android.applicationVariants.all { variant ->
    variant.outputs.each { output ->
      output.versionCodeOverride =
          project.ext.versionCodes.get(output.getFilter(com.android.build.OutputFile.ABI), 0) * 1000000 + android.defaultConfig.versionCode
    }
  }
}

dependencies {
  implementation fileTree(dir: 'libs', include: ['*.jar'])
  implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
  implementation 'androidx.appcompat:appcompat:1.1.0'
  implementation 'androidx.core:core-ktx:1.2.0'
  implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
  testImplementation 'junit:junit:4.12'
  androidTestImplementation 'androidx.test.ext:junit:1.1.1'
  androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
}

使用

我们将一张彩色图片通过 opencv 处理成一张灰色的照片。

1、编写处理照片的代码。

创建native代码

object NativeLibUtils{

  init {
    System.loadLibrary("native-lib")
  }

  external fun bitmap2Grey(pixels: IntArray, w: Int, h: Int): IntArray
}

创建 jni 代码

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

using namespace cv;
using namespace std;


extern "C"
JNIEXPORT jintArray JNICALL
Java_com_mp5a5_opencv_NativeLibUtils_bitmap2Gray(JNIEnv *env, jobject instance, jintArray pixels,
                         jint w, jint h) {
  jint *cur_array;

  jboolean isCopy = static_cast(false);

  cur_array = env->GetIntArrayElements(pixels, &isCopy);
  if (cur_array == NULL) {
    return 0;
  }

  Mat img(h, w, CV_8UC4, (unsigned char *) cur_array);

  cvtColor(img, img, CV_BGRA2GRAY);
  cvtColor(img, img, CV_GRAY2BGRA);

  int size = w * h;
  jintArray result = env->NewIntArray(size);
  env->SetIntArrayRegion(result, 0, size, (jint *) img.data);
  env->ReleaseIntArrayElements(pixels, cur_array, 0);
  return result;
}

调用 native 代码来实现彩色图片转换成灰色图片

private fun showGrayImg() {
  val w = bitmap.width
  val h = bitmap.height
  val pixels = IntArray(w * h)
  bitmap.getPixels(pixels, 0, w, 0, 0, w, h)
  val resultData: IntArray = NativeLibUtils.bitmap2Gray(pixels, w, h)
  val resultImage = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888)
  resultImage.setPixels(resultData, 0, w, 0, 0, w, h)
  iv_image.setImageBitmap(resultImage)
}

完整转换的代码

class OpenCvActivity : AppCompatActivity(), View.OnClickListener {

  private lateinit var bitmap: Bitmap

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_opencv)
    bitmap = BitmapFactory.decodeResource(resources, R.mipmap.person)
    iv_image.setImageBitmap(bitmap)
    btn_btn1.setOnClickListener(this)
    btn_btn2.setOnClickListener(this)
  }

  override fun onClick(v: View?) {
    v?.id?.let {
      when (it) {
        R.id.btn_btn1 -> {
          showGrayImg()
        }
        R.id.btn_btn2 -> {
          showRgbImg()
        }
      }
    }
  }

  private fun showRgbImg() {
    bitmap = BitmapFactory.decodeResource(resources, R.mipmap.person)
    iv_image.setImageBitmap(bitmap)
  }

  private fun showGrayImg() {
    val w = bitmap.width
    val h = bitmap.height
    val pixels = IntArray(w * h)
    bitmap.getPixels(pixels, 0, w, 0, 0, w, h)
    val resultData: IntArray = NativeLibUtils.bitmap2Gray(pixels, w, h)
    val resultImage = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888)
    resultImage.setPixels(resultData, 0, w, 0, 0, w, h)
    iv_image.setImageBitmap(resultImage)
  }
}

<?xml version="1.0" encoding="utf-8"?>

显示效果：

Android如何通过cmake的方式接入opencv

效果图

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Android如何通过cmake的方式接入opencv

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