add basic support for focus and metering

app/src/main/kotlin/com/simplemobiletools/camera/activities/MainActivity.kt

@@ -568,6 +568,10 @@ class MainActivity : SimpleActivity(), PhotoProcessor.MediaSavedListener, Camera
         video_rec_curr_timer.text = seconds.getFormattedDuration()
     }
 
+    override fun onFocusCamera(xPos: Float, yPos: Float) {
+        mFocusCircleView.drawFocusCircle(xPos, yPos)
+    }
+
     fun setRecordingState(isRecording: Boolean) {
         runOnUiThread {
             if (isRecording) {

app/src/main/kotlin/com/simplemobiletools/camera/implementations/CameraXPreview.kt

@@ -7,6 +7,9 @@ import android.net.Uri
 import android.os.Environment
 import android.provider.MediaStore
 import android.util.Log
+import android.view.GestureDetector
+import android.view.GestureDetector.SimpleOnGestureListener
+import android.view.MotionEvent
 import android.view.OrientationEventListener
 import android.view.Surface
 import androidx.appcompat.app.AppCompatActivity
@@ -152,6 +155,7 @@ class CameraXPreview(
             captureUseCase,
         )
         preview?.setSurfaceProvider(viewFinder.surfaceProvider)
+        setupFocus()
     }
 
     private fun setupCameraObservers() {
@@ -261,6 +265,38 @@ class CameraXPreview(
         return AspectRatio.RATIO_16_9
     }
 
+    @SuppressLint("ClickableViewAccessibility")
+    // source: https://stackoverflow.com/a/60095886/10552591
+    private fun setupFocus() {
+        val gestureDetector = GestureDetector(activity, object : SimpleOnGestureListener() {
+            override fun onSingleTapConfirmed(event: MotionEvent?): Boolean {
+                Log.i(TAG, "onSingleTapConfirmed: x=${event?.x}, y=${event?.y}")
+                return event?.let {
+                    val factory: MeteringPointFactory = SurfaceOrientedMeteringPointFactory(viewFinder.width.toFloat(), viewFinder.height.toFloat())
+                    val xPos = event.x
+                    val yPos = event.y
+                    val autoFocusPoint = factory.createPoint(event.x, event.y)
+                    try {
+                        val focusMeteringAction = FocusMeteringAction.Builder(autoFocusPoint, FocusMeteringAction.FLAG_AF)
+                            .disableAutoCancel()
+                            .build()
+                        camera?.cameraControl?.startFocusAndMetering(focusMeteringAction)
+                        listener.onFocusCamera(xPos, yPos)
+                        Log.i(TAG, "start focus")
+                    } catch (e: CameraInfoUnavailableException) {
+                        Log.e(TAG, "cannot access camera", e)
+                    }
+                    true
+                } ?: false
+            }
+        })
+        viewFinder.setOnTouchListener { _, event ->
+            Log.i(TAG, "setOnTouchListener: x=${event.x}, y=${event.y}")
+            gestureDetector.onTouchEvent(event)
+            true
+        }
+    }
+
     override fun onStart(owner: LifecycleOwner) {
         orientationEventListener.enable()
     }

app/src/main/kotlin/com/simplemobiletools/camera/implementations/CameraXPreviewListener.kt

@@ -13,4 +13,5 @@ interface CameraXPreviewListener {
     fun onVideoRecordingStarted()
     fun onVideoRecordingStopped()
     fun onVideoDurationChanged(durationNanos: Long)
+    fun onFocusCamera(xPos: Float, yPos: Float)
 }