MainActivity.kt

package com.example.nativeopencvandroidtemplate

import android.Manifest
import android.app.Activity
import android.content.pm.PackageManager
import android.os.Bundle
import androidx.core.app.ActivityCompat
import android.util.Log
import android.view.SurfaceView
import android.view.WindowManager
import android.widget.Toast
import org.opencv.android.CameraBridgeViewBase
import org.opencv.android.OpenCVLoader
import org.opencv.core.Mat

class MainActivity : Activity(), CameraBridgeViewBase.CvCameraViewListener2 {

    private var mOpenCvCameraView: CameraBridgeViewBase? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        window.addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON)

        // Request camera permission
        ActivityCompat.requestPermissions(
            this,
            arrayOf(Manifest.permission.CAMERA),
            CAMERA_PERMISSION_REQUEST
        )

        setContentView(R.layout.activity_main)

        mOpenCvCameraView = findViewById<CameraBridgeViewBase>(R.id.main_surface)
        mOpenCvCameraView?.apply {
            visibility = SurfaceView.VISIBLE
            setCvCameraViewListener(this@MainActivity)
        }
    }

    override fun onRequestPermissionsResult(
        requestCode: Int,
        permissions: Array<String>,
        grantResults: IntArray
    ) {
        when (requestCode) {
            CAMERA_PERMISSION_REQUEST -> {
                if (grantResults.isNotEmpty() && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    mOpenCvCameraView?.setCameraPermissionGranted()
                } else {
                    Toast.makeText(this, "Camera permission required", Toast.LENGTH_LONG).show()
                }
            }
        }
    }

    override fun onResume() {
        super.onResume()

        // Initialize OpenCV
        if (!OpenCVLoader.initLocal()) {
            Log.e(TAG, "OpenCV initialization failed")
            Toast.makeText(this, "OpenCV initialization failed", Toast.LENGTH_LONG).show()
            return
        }

        // Load native library
        try {
            System.loadLibrary("native-lib")
        } catch (e: UnsatisfiedLinkError) {
            Log.e(TAG, "Failed to load native library: ${e.message}")
            Toast.makeText(this, "Failed to load native library", Toast.LENGTH_LONG).show()
            return
        }

        mOpenCvCameraView?.enableView()
    }

    override fun onPause() {
        super.onPause()
        mOpenCvCameraView?.disableView()
    }

    override fun onDestroy() {
        super.onDestroy()
        mOpenCvCameraView?.disableView()
    }

    override fun onCameraViewStarted(width: Int, height: Int) {}

    override fun onCameraViewStopped() {}

    override fun onCameraFrame(frame: CameraBridgeViewBase.CvCameraViewFrame): Mat {
        // Get current camera frame as grayscale
        val mat = frame.gray()

        // Process frame with native code
        adaptiveThresholdFromJNI(mat.nativeObjAddr)

        return mat
    }

    private external fun adaptiveThresholdFromJNI(matAddr: Long)

    companion object {
        private const val TAG = "MainActivity"
        private const val CAMERA_PERMISSION_REQUEST = 1
    }
}