Improve the long press to zoom feature.

lib/pages/reader/images.dart

@@ -115,6 +115,10 @@ class _GalleryModeState extends State<_GalleryMode>
 
   var imageStates = <State<ComicImage>>{};
 
+  bool isLongPressing = false;
+
+  int fingers = 0;
+
   @override
   void initState() {
     reader = context.reader;
@@ -144,7 +148,28 @@ class _GalleryModeState extends State<_GalleryMode>
 
   @override
   Widget build(BuildContext context) {
-    return PhotoViewGallery.builder(
+    return Listener(
+      onPointerDown: (event) {
+        fingers++;
+      },
+      onPointerUp: (event) {
+        fingers--;
+      },
+      onPointerCancel: (event) {
+        fingers--;
+      },
+      onPointerMove: (event) {
+        if (isLongPressing) {
+          var controller = photoViewControllers[reader.page]!;
+          Offset value = event.delta;
+          if (isLongPressing) {
+            controller.updateMultiple(
+              position: controller.position + value,
+            );
+          }
+        }
+      },
+      child: PhotoViewGallery.builder(
         backgroundDecoration: BoxDecoration(
           color: context.colorScheme.surface,
         ),
@@ -219,6 +244,7 @@ class _GalleryModeState extends State<_GalleryMode>
             context.readerScaffold.update();
           }
         },
+      ),
     );
   }
 
@@ -312,7 +338,7 @@ class _GalleryModeState extends State<_GalleryMode>
 
   @override
   void handleLongPressDown(Offset location) {
-    if (!appdata.settings['enableLongPressToZoom']) {
+    if (!appdata.settings['enableLongPressToZoom'] || fingers != 1) {
       return;
     }
     var photoViewController = photoViewControllers[reader.page]!;
@@ -322,16 +348,18 @@ class _GalleryModeState extends State<_GalleryMode>
       target,
       Offset(size.width / 2 - location.dx, size.height / 2 - location.dy),
     );
+    isLongPressing = true;
   }
 
   @override
   void handleLongPressUp(Offset location) {
-    if (!appdata.settings['enableLongPressToZoom']) {
+    if (!appdata.settings['enableLongPressToZoom'] || !isLongPressing) {
       return;
     }
     var photoViewController = photoViewControllers[reader.page]!;
     double target = photoViewController.getInitialScale!.call()!;
     photoViewController.animateScale?.call(target);
+    isLongPressing = false;
   }
 
   Timer? keyRepeatTimer;