Reenable hero using the thumbnail

app/lib/flutter_util.dart

@@ -19,3 +19,44 @@ class CustomizableMaterialPageRoute extends MaterialPageRoute {
 }
 
 String getImageHeroTag(FileDescriptor file) => "imageHero(${file.fdPath})";
+
+// copied from flutter
+Widget defaultHeroFlightShuttleBuilder(
+  BuildContext flightContext,
+  Animation<double> animation,
+  HeroFlightDirection flightDirection,
+  BuildContext fromHeroContext,
+  BuildContext toHeroContext,
+) {
+  final Hero toHero = toHeroContext.widget as Hero;
+
+  final MediaQueryData? toMediaQueryData = MediaQuery.maybeOf(toHeroContext);
+  final MediaQueryData? fromMediaQueryData =
+      MediaQuery.maybeOf(fromHeroContext);
+
+  if (toMediaQueryData == null || fromMediaQueryData == null) {
+    return toHero.child;
+  }
+
+  final EdgeInsets fromHeroPadding = fromMediaQueryData.padding;
+  final EdgeInsets toHeroPadding = toMediaQueryData.padding;
+
+  return AnimatedBuilder(
+    animation: animation,
+    builder: (BuildContext context, Widget? child) {
+      return MediaQuery(
+          data: toMediaQueryData.copyWith(
+            padding: (flightDirection == HeroFlightDirection.push)
+                ? EdgeInsetsTween(
+                    begin: fromHeroPadding,
+                    end: toHeroPadding,
+                  ).evaluate(animation)
+                : EdgeInsetsTween(
+                    begin: toHeroPadding,
+                    end: fromHeroPadding,
+                  ).evaluate(animation),
+          ),
+          child: toHero.child);
+    },
+  );
+}

app/lib/widget/image_viewer.dart

@@ -1,3 +1,4 @@
+import 'package:cached_network_image/cached_network_image.dart';
 import 'package:cached_network_image_platform_interface/cached_network_image_platform_interface.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/widgets.dart';
@@ -8,9 +9,11 @@ import 'package:nc_photos/api/api_util.dart' as api_util;
 import 'package:nc_photos/cache_manager_util.dart';
 import 'package:nc_photos/entity/file_descriptor.dart';
 import 'package:nc_photos/entity/local_file.dart';
+import 'package:nc_photos/flutter_util.dart' as flutter_util;
 import 'package:nc_photos/k.dart' as k;
 import 'package:nc_photos/mobile/android/content_uri_image_provider.dart';
 import 'package:nc_photos/widget/cached_network_image_mod.dart' as mod;
+import 'package:nc_photos/widget/network_thumbnail.dart';
 import 'package:np_codegen/np_codegen.dart';
 
 part 'image_viewer.g.dart';
@@ -113,16 +116,61 @@ class RemoteImageViewer extends StatefulWidget {
 @npLog
 class _RemoteImageViewerState extends State<RemoteImageViewer> {
   @override
-  build(BuildContext context) => _ImageViewer(
+  void initState() {
+    super.initState();
+    WidgetsBinding.instance.addPostFrameCallback((_) {
+      if (mounted) {
+        // needed to get rid of the large image blinking during Hero animation
+        setState(() {});
+      }
+    });
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return _ImageViewer(
       canZoom: widget.canZoom,
       onHeightChanged: widget.onHeightChanged,
       onZoomStarted: widget.onZoomStarted,
       onZoomEnded: widget.onZoomEnded,
-        child: mod.CachedNetworkImage(
+      child: Stack(
+        fit: StackFit.passthrough,
+        children: [
+          Hero(
+            tag: flutter_util.getImageHeroTag(widget.file),
+            flightShuttleBuilder: (flightContext, animation, flightDirection,
+                fromHeroContext, toHeroContext) {
+              _isHeroDone = false;
+              animation.addStatusListener(_animationListener);
+              return flutter_util.defaultHeroFlightShuttleBuilder(
+                flightContext,
+                animation,
+                flightDirection,
+                fromHeroContext,
+                toHeroContext,
+              );
+            },
+            child: CachedNetworkImage(
+              fit: BoxFit.contain,
+              cacheManager: ThumbnailCacheManager.inst,
+              imageUrl: NetworkRectThumbnail.imageUrlForFile(
+                  widget.account, widget.file),
+              httpHeaders: {
+                "Authorization":
+                    Api.getAuthorizationHeaderValue(widget.account),
+              },
+              fadeInDuration: const Duration(),
+              filterQuality: FilterQuality.high,
+              imageRenderMethodForWeb: ImageRenderMethodForWeb.HttpGet,
+            ),
+          ),
+          if (_isHeroDone)
+            mod.CachedNetworkImage(
               cacheManager: LargeImageCacheManager.inst,
               imageUrl: _getImageUrl(widget.account, widget.file),
               httpHeaders: {
-            "Authorization": Api.getAuthorizationHeaderValue(widget.account),
+                "Authorization":
+                    Api.getAuthorizationHeaderValue(widget.account),
               },
               fit: BoxFit.contain,
               fadeInDuration: const Duration(),
@@ -136,7 +184,10 @@ class _RemoteImageViewerState extends State<RemoteImageViewer> {
                 return child;
               },
             ),
+        ],
+      ),
     );
+  }
 
   void _onItemLoaded() {
     if (!_isLoaded) {
@@ -146,7 +197,19 @@ class _RemoteImageViewerState extends State<RemoteImageViewer> {
     }
   }
 
+  void _animationListener(AnimationStatus status) {
+    if (status == AnimationStatus.completed) {
+      _isHeroDone = true;
+      if (mounted) {
+        setState(() {});
+      }
+    }
+  }
+
   var _isLoaded = false;
+  // initially set to true such that the large image will show when hero didn't
+  // run (i.e., when swiping in viewer)
+  var _isHeroDone = true;
 }
 
 class _ImageViewer extends StatefulWidget {

app/lib/widget/photo_list_item.dart

@@ -6,6 +6,7 @@ import 'package:nc_photos/account.dart';
 import 'package:nc_photos/app_localizations.dart';
 import 'package:nc_photos/entity/file_descriptor.dart';
 import 'package:nc_photos/entity/local_file.dart';
+import 'package:nc_photos/flutter_util.dart' as flutter_util;
 import 'package:nc_photos/k.dart' as k;
 import 'package:nc_photos/mobile/android/content_uri_image_provider.dart';
 import 'package:nc_photos/theme.dart';
@@ -63,6 +64,7 @@ class PhotoListImageItem extends PhotoListFileItem {
         previewUrl: previewUrl,
         isGif: file.fdMime == "image/gif",
         isFavorite: shouldShowFavoriteBadge && file.fdIsFavorite == true,
+        heroKey: flutter_util.getImageHeroTag(file),
       );
 
   final Account account;