Android-Kotlin-Native-CV-Examples

This is a Android Studio Kotlin project to demo some OpenCV operations. Some examples include native OpenCV functions and JNI calls.

Requirement:

Android Studio 3+

OpenCV version: 3.4.1

How to create the native OpenCV project

Make sure you have Android SDK up to date, with NDK installed and CMake
Download OpenCV SDK for Android from OpenCV.org and decompress the zip file
Create a new Android Studio project
- Check Include C++ and Kotlin support
- Choose empty Activity
- In C++ Support, you can check -fexceptions and -frtti
Import OpenCV library module
- New -> Import Module
- Choose the YOUR_OPENCV_SDK/sdk/java folder
- Unckeck replace jar, unckeck replace lib, unckeck create gradle-style
- Set the OpenCV library module up to fit your SDK
  
  Edit openCVLibrary/build.gradle to fit your SDK:
```
compileSdkVersion 28
defaultConfig {
    minSdkVersion 25
    targetSdkVersion 28
}
```
- Add OpenCV module dependency in your app module
  - File -> Project structure -> Module app -> Dependencies tab -> New module dependency -> choose OpenCV library module

Create a folder named jniLibs in app/src/main and copy the files from YOUR_OPENCV_SDK/sdk/native/libs to that folder

Set the app build.gradle

Add abiFilters

externalNativeBuild {
    cmake {
        cppFlags "-frtti -fexceptions"
        abiFilters 'x86', 'x86_64', 'armeabi-v7a', 'arm64-v8a'
    }
}

Add openCV jniLibs directory to point to the libs

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

Create a folder named include in app/src/main/cpp/include and copy the header files from YOUR_OPENCV_SDK/sdk/native/jni/include.

Configure the CMakeLists.txt file

After the cmake_minimum_required, add

include_directories(src/main/cpp/include)
add_library( lib_opencv SHARED IMPORTED )
set_target_properties(lib_opencv PROPERTIES IMPORTED_LOCATION ${CMAKE_CURRENT_SOURCE_DIR}/src/main/jniLibs/${ANDROID_ABI}/libopencv_java3.so)

At the end of the file add lib_opencv to the target_link_libraries list

target_link_libraries(
        native-lib
        lib_opencv
        ${log-lib})

Grant camera permission

Add the following lines in the AndroidManifest.xml file

<uses-permission android:name="android.permission.CAMERA"/>
<uses-feature android:name="android.hardware.camera"/>
<uses-feature android:name="android.hardware.camera.autofocus"/>
<uses-feature android:name="android.hardware.camera.front"/>
<uses-feature android:name="android.hardware.camera.front.autofocus"/>

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