Recalculate EV on Iso change

lib/screens/metering/components/topbar/topbar.dart

@@ -18,6 +18,7 @@ class MeteringTopBar extends StatelessWidget {
   final double ev;
   final IsoValue iso;
   final double nd;
+  final ValueChanged<IsoValue> onIsoChanged;
 
   MeteringTopBar({
     required this.fastest,
@@ -25,6 +26,7 @@ class MeteringTopBar extends StatelessWidget {
     required this.ev,
     required this.iso,
     required this.nd,
+    required this.onIsoChanged,
     super.key,
   });
 
@@ -108,7 +110,7 @@ class MeteringTopBar extends StatelessWidget {
                                     _isoDialogKey.currentState?.close();
                                   },
                                   onSelect: (value) {
-                                    _isoDialogKey.currentState?.close();
+                                    _isoDialogKey.currentState?.close().then((_) => onIsoChanged(value));
                                   },
                                 ),
                               ),

lib/screens/metering/metering_bloc.dart

@@ -3,6 +3,7 @@ import 'dart:math';
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:lightmeter/models/exposure_pair.dart';
 import 'package:lightmeter/models/photography_value.dart';
+import 'package:lightmeter/utils/log_2.dart';
 
 import 'metering_event.dart';
 import 'metering_state.dart';
@@ -24,11 +25,23 @@ class MeteringBloc extends Bloc<MeteringEvent, MeteringState> {
             exposurePairs: [],
           ),
         ) {
+    on<IsoChangedEvent>(_onIsoChanged);
     on<MeasureEvent>(_onMeasure);
 
     add(const MeasureEvent());
   }
 
+  void _onIsoChanged(IsoChangedEvent event, Emitter emit) {
+    final ev = state.ev + log2(event.isoValue.value / state.iso.value);
+    emit(MeteringState(
+      iso: event.isoValue,
+      ev: ev,
+      evCompensation: state.evCompensation,
+      nd: state.nd,
+      exposurePairs: _buildExposureValues(ev),
+    ));
+  }
+
   /// https://www.scantips.com/lights/exposurecalc.html
   void _onMeasure(_, Emitter emit) {
     double log2(double x) => log(x) / log(2);
@@ -39,14 +52,13 @@ class MeteringBloc extends Bloc<MeteringEvent, MeteringState> {
 
     final evAtSystemIso = log2(pow(aperture.value, 2).toDouble()) - log2(shutterSpeed.value);
     final ev = evAtSystemIso - log2(iso.value / state.iso.value);
-    final exposurePairs = _buildExposureValues(ev);
 
     emit(MeteringState(
       iso: state.iso,
       ev: ev,
       evCompensation: state.evCompensation,
       nd: state.nd,
-      exposurePairs: exposurePairs,
+      exposurePairs: _buildExposureValues(ev),
     ));
   }
 

lib/screens/metering/metering_event.dart

@@ -1,7 +1,15 @@
+import 'package:lightmeter/models/photography_value.dart';
+
 abstract class MeteringEvent {
   const MeteringEvent();
 }
 
+class IsoChangedEvent extends MeteringEvent {
+  final IsoValue isoValue;
+
+  const IsoChangedEvent(this.isoValue);
+}
+
 class MeasureEvent extends MeteringEvent {
   const MeasureEvent();
 }

lib/screens/metering/metering_screen.dart

@@ -112,6 +112,7 @@ class _MeteringScreenState extends State<MeteringScreen> {
       ev: state.ev,
       iso: state.iso,
       nd: state.nd,
+      onIsoChanged: (value) => context.read<MeteringBloc>().add(IsoChangedEvent(value)),
     );
   }
 

lib/utils/log_2.dart

@@ -0,0 +1,3 @@
+import 'dart:math';
+
+double log2(double x) => log(x) / log(2);