Android Studio NDK + OpenCV + CPP 測試程式（二十四）：

Android Studio NDK + OpenCV + CPP 測試程式（二十四）：

完成了 NDK（Native Development Kit）和 OpenCV 安裝和設置後，便可以測試 OpenCV 的 C++ 程式，現在 Android Studio 中已經可以調用 OpenCV 的C/C++。

Android Studio 的 NDK + OpenCV + CPP 測試程式

操作系統：Windows 7 64-bit 版本
開發環境：Android Studio 4.0.1 版本
Gradle 版本：6.1.1
手機測試版本：API 19
原程式：C:\Development\Development_Android\Android_Project\NDK
程式：C:\Development\Development_Android\Android_Project\NDK
NDK 版本：NDK 21.0.6113669 版本 Android

1﹒在 MainActivity有 Java 中載入庫，用作運行 APP。程式內用 native 方法聲明和調用 int[] Bitmap2Grey 和 String stringFromJNI()，Bitmap2Grey 用來轉換灰階圖像。
app / java / MainActivity.java：

package bugworkshop.blogspot.ndk;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;

import android.widget.TextView;

import org.opencv.android.OpenCVLoader;

import android.util.Log;

import android.graphics.Bitmap;

import android.graphics.BitmapFactory;

import android.view.View;

import android.widget.Button;

import android.widget.ImageView;

import android.widget.Toast;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

// Used to load the 'native-lib' library on application startup.

static {

System.loadLibrary("native-lib");

}

private Button btn_1;

private Button btn_2;

private ImageView imageView;

private Bitmap bitmap;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

// Example of a call to a native method

TextView tv = findViewById(R.id.sample_text);

tv.setText(stringFromJNI());

Toast.makeText(MainActivity.this, stringFromJNI(),Toast.LENGTH_LONG).show();

if (OpenCVLoader.initDebug()) {

Log.i("CV", "Load OpenCV Library Successful.");

tv.setText("Load OpenCV Library Successfully.");

} else {

Log.i("CV", "Load OpenCV Library Failed.");

tv.setText("Load OpenCV Library Failed.");;

}

btn_1 = (Button)findViewById(R.id.button_1);

imageView = (ImageView)findViewById(R.id.image);

bitmap = BitmapFactory.decodeResource(getResources(),R.drawable.face01);

btn_1.setOnClickListener(this);

btn_2 = (Button)findViewById(R.id.button_2);

btn_2.setOnClickListener(this);

}

public void showImage(){

bitmap = BitmapFactory.decodeResource(getResources(),R.drawable.face01);

imageView.setImageBitmap(bitmap);

}

public void gray(){

int w = bitmap.getWidth();

int h = bitmap.getHeight();

int[] piexls = new int[w*h];

bitmap.getPixels(piexls,0,w,0,0,w,h);

int[] resultData =Bitmap2Grey(piexls,w,h);

Bitmap resultImage = Bitmap.createBitmap(w,h, Bitmap.Config.ARGB_8888);

resultImage.setPixels(resultData,0,w,0,0,w,h);

imageView.setImageBitmap(resultImage);

}

@Override

public void onClick(View view){

switch(view.getId()){

case R.id.button_1:showImage();break;

case R.id.button_2:gray();break;

}

/**

* A native method that is implemented by the 'native-lib' native library,

* which is packaged with this application.

public native int[] Bitmap2Grey(int[] pixels,int w,int h);

/**

* A native method that is implemented by the 'native-lib' native library,

* which is packaged with this application.

public native String stringFromJNI();

@Override

public void onResume(){

super.onResume();

}

2﹒native-lib.cpp 是 C++ 程式。
app / cpp / native-lib.cpp：

#include<opencv2/opencv.hpp>

using namespace cv;

using namespace std;

extern "C"

JNIEXPORT jintArray JNICALL

Java_bugworkshop_blogspot_ndk_MainActivity_Bitmap2Grey(

JNIEnv *env,

jobject /* this */,jintArray buf,jint w,jint h) {

jint *cbuf;

jboolean ptfalse = false;

//讀取 int 陣列並轉為 Mat 類型

cbuf = env->GetIntArrayElements(buf, &ptfalse);

if(cbuf == NULL){

return 0;

}

Mat imgData(h, w, CV_8UC4, (unsigned char*)cbuf);

// 注意，Android 的 Bitmap 是 ARGB 四通道,而不是 RGB 三通道

cvtColor(imgData,imgData,CV_BGRA2GRAY);

cvtColor(imgData,imgData,CV_GRAY2BGRA);

int size=w * h;

jintArray result = env->NewIntArray(size);

env->SetIntArrayRegion(result, 0, size, (jint*)imgData.data);

env->ReleaseIntArrayElements(buf, cbuf, 0);

return result;

}

extern "C"

JNIEXPORT jstring JNICALL

Java_bugworkshop_blogspot_ndk_MainActivity_stringFromJNI(

JNIEnv* env,

jobject /* this */) {

std::string hello = "Hello from C++";

return env->NewStringUTF(hello.c_str());

}

3﹒介面內容佈局。
app / res / layout / active_main.xml：

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

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:app="http://schemas.android.com/apk/res-auto"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:orientation="vertical"

tools:context=".MainActivity">

<LinearLayout

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:layout_weight="1"

android:orientation="vertical">

<TextView

android:id="@+id/sample_text"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="Hello World!"

app:layout_constraintBottom_toBottomOf="parent"

app:layout_constraintLeft_toLeftOf="parent"

app:layout_constraintRight_toRightOf="parent"

app:layout_constraintTop_toTopOf="parent" />

<ImageView

android:id="@+id/image"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:layout_weight="1"

app:srcCompat="@drawable/face01" />

</LinearLayout>

<LinearLayout

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:layout_weight="1"

android:orientation="horizontal">

<Button

android:id="@+id/button_2"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:layout_weight="1"

android:text="Gray" />

<Button

android:id="@+id/button_1"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:layout_weight="1"

android:text="Color" />

</LinearLayout>

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