[android] calculate EFL

android/app/src/main/kotlin/com/vodemn/lightmeter/MainActivity.kt

@@ -4,6 +4,7 @@ import android.os.Bundle
 import android.view.KeyEvent
 import android.view.WindowManager
 import androidx.core.view.WindowCompat
+import com.vodemn.lightmeter.PlatformChannels.CameraInfoPlatformChannel
 import io.flutter.embedding.android.FlutterActivity
 import io.flutter.embedding.engine.FlutterEngine
 import io.flutter.plugin.common.EventChannel
@@ -17,6 +18,8 @@ class MainActivity : FlutterActivity() {
     private var volumeEventsEmitter: EventSink? = null
     private var handleVolume = false
 
+    private val cameraInfoPlatformChannel = CameraInfoPlatformChannel()
+
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         WindowCompat.setDecorFitsSystemWindows(window, false)
@@ -24,6 +27,8 @@ class MainActivity : FlutterActivity() {
 
     override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
         super.configureFlutterEngine(flutterEngine)
+        cameraInfoPlatformChannel.onAttachedToEngine(flutterEngine.dartExecutor.binaryMessenger, context)
+
         keepScreenOnChannel = MethodChannel(
             flutterEngine.dartExecutor.binaryMessenger,
             "com.vodemn.lightmeter/keepScreenOn"
@@ -76,6 +81,7 @@ class MainActivity : FlutterActivity() {
         keepScreenOnChannel.setMethodCallHandler(null)
         volumeHandlingChannel.setMethodCallHandler(null)
         volumeEventChannel.setStreamHandler(null)
+        cameraInfoPlatformChannel.onDestroy()
         super.onDestroy()
     }
 

android/app/src/main/kotlin/com/vodemn/lightmeter/PlatformChannels/CameraInfoPlatformChannel.kt

@@ -0,0 +1,57 @@
+package com.vodemn.lightmeter.PlatformChannels
+
+import android.content.Context
+import android.hardware.camera2.CameraCharacteristics
+import android.hardware.camera2.CameraManager
+import android.hardware.camera2.CameraMetadata.LENS_FACING_BACK
+import io.flutter.plugin.common.BinaryMessenger
+import io.flutter.plugin.common.MethodCall
+import io.flutter.plugin.common.MethodChannel
+import kotlin.math.pow
+import kotlin.math.sqrt
+
+/** CameraInfoPlatformChannel */
+class CameraInfoPlatformChannel : MethodChannel.MethodCallHandler {
+    private lateinit var channel: MethodChannel
+    private lateinit var cameraManager: CameraManager
+    private var mainCameraEfl: Double? = null
+
+    fun onAttachedToEngine(binaryMessenger: BinaryMessenger, context: Context) {
+        channel = MethodChannel(binaryMessenger, "com.vodemn.lightmeter.CameraInfoPlatformChannel")
+        cameraManager = context.getSystemService(Context.CAMERA_SERVICE) as CameraManager
+        channel.setMethodCallHandler(this)
+    }
+
+    override fun onMethodCall(call: MethodCall, result: MethodChannel.Result) {
+        when (call.method) {
+            "mainCameraEfl" -> {
+                mainCameraEfl = mainCameraEfl ?: getMainCameraFocalLength35mm()
+                result.success(mainCameraEfl)
+            }
+            else -> result.notImplemented()
+        }
+    }
+
+    fun onDestroy() {
+        channel.setMethodCallHandler(null)
+    }
+
+    private fun getMainCameraFocalLength35mm(): Double? {
+        return cameraManager.cameraIdList.map {
+            cameraManager.getCameraCharacteristics(it)
+        }.first {
+            it.get(CameraCharacteristics.LENS_FACING) == LENS_FACING_BACK
+        }.focalLength35mm()
+    }
+
+    private fun CameraCharacteristics.focalLength35mm(): Double? {
+        val defaultFocalLength = get(CameraCharacteristics.LENS_INFO_AVAILABLE_FOCAL_LENGTHS)?.first()
+        val sensorSize = get(CameraCharacteristics.SENSOR_INFO_PHYSICAL_SIZE)
+        return if (defaultFocalLength != null && sensorSize != null) {
+            // https://en.wikipedia.org/wiki/35_mm_equivalent_focal_length#Conversions
+            43.27 * defaultFocalLength / sqrt(sensorSize.height.pow(2) + sensorSize.width.pow(2))
+        } else {
+            null
+        }
+    }
+}

lib/application_wrapper.dart

@@ -5,6 +5,7 @@ import 'package:flutter_native_splash/flutter_native_splash.dart';
 import 'package:lightmeter/data/analytics/analytics.dart';
 import 'package:lightmeter/data/analytics/api/analytics_firebase.dart';
 import 'package:lightmeter/data/caffeine_service.dart';
+import 'package:lightmeter/data/camera_info_service.dart';
 import 'package:lightmeter/data/haptics_service.dart';
 import 'package:lightmeter/data/light_sensor_service.dart';
 import 'package:lightmeter/data/permissions_service.dart';
@@ -99,11 +100,13 @@ class _ApplicationWrapperState extends State<ApplicationWrapper> {
     await Future.wait([
       SharedPreferences.getInstance(),
       const LightSensorService(LocalPlatform()).hasSensor(),
+      const CameraInfoService().mainCameraEfl(),
       remoteConfigService.activeAndFetchFeatures(),
       equipmentProfilesStorageService.init(),
       filmsStorageService.init(),
     ]).then((value) {
-      userPreferencesService = UserPreferencesService((value[0] as SharedPreferences?)!);
+      userPreferencesService = UserPreferencesService((value[0] as SharedPreferences?)!)
+        ..cameraFocalLength = value[2] as int?;
       hasLightSensor = value[1] as bool? ?? false;
     });
   }

lib/data/camera_info_service.dart

@@ -0,0 +1,18 @@
+import 'dart:io';
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/services.dart';
+
+class CameraInfoService {
+  @visibleForTesting
+  static const cameraInfoPlatformChannel = MethodChannel("com.vodemn.lightmeter.CameraInfoPlatformChannel");
+
+  const CameraInfoService();
+
+  Future<int?> mainCameraEfl() async {
+    if (Platform.isIOS) {
+      return null;
+    }
+    return (await cameraInfoPlatformChannel.invokeMethod<double?>('mainCameraEfl'))?.round();
+  }
+}