From a42896f61242f0588623c461bfd9a9a34171ec37 Mon Sep 17 00:00:00 2001
From: Julian Mutter <julian.mutter@comumail.de>
Date: Wed, 22 Oct 2025 19:15:35 +0200
Subject: [PATCH] change two-page turn to happen after half of pdf page

---
 lib/sheet_viewer_page.dart | 54 +++++++++++++++++++++++++++++++-------
 1 file changed, 44 insertions(+), 10 deletions(-)

diff --git a/lib/sheet_viewer_page.dart b/lib/sheet_viewer_page.dart
index 7f09ffa..9c59c0b 100644
--- a/lib/sheet_viewer_page.dart
+++ b/lib/sheet_viewer_page.dart
@@ -1,3 +1,5 @@
+import 'dart:math';
+
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
@@ -9,6 +11,7 @@ import 'package:sheetless/bt_pedal_shortcuts.dart';
 import 'package:sheetless/sheet.dart';
 import 'package:sheetless/storage_helper.dart';
 import 'package:flutter_fullscreen/flutter_fullscreen.dart';
+import 'package:sheetless/utility.dart';
 
 class SheetViewerPage extends StatefulWidget {
   final Sheet sheet;
@@ -224,19 +227,25 @@ class TouchablePages extends StatelessWidget {
 
         final touchAreaWidth = mediaQuery.size.width;
 
+        final (leftPageSize, rightPageSize) = pages.calcPageSizesScaled(
+          mediaQuery.size,
+        );
+
         if (details.localPosition.dy < 2 * pixelsPerCm &&
             details.localPosition.dx >= touchAreaWidth - 2 * pixelsPerCm &&
             pages.config.fullscreen) {
           onExitSheetViewer();
         } else if (details.localPosition.dy < 2 * pixelsPerCm) {
           onToggleFullscreen();
-        } else if (details.localPosition.dx < touchAreaWidth / 4 &&
-            pages.config.twoPageMode) {
+        } else if (pages.config.twoPageMode &&
+            details.localPosition.dx <
+                touchAreaWidth / 2 - leftPageSize.width / 2) {
           onTurnPage(-2);
         } else if (details.localPosition.dx < touchAreaWidth / 2) {
           onTurnPage(-1);
-        } else if (details.localPosition.dx > touchAreaWidth * 3 / 4 &&
-            pages.config.twoPageMode) {
+        } else if (pages.config.twoPageMode &&
+            details.localPosition.dx >
+                touchAreaWidth / 2 + rightPageSize!.width / 2) {
           onTurnPage(2);
         } else {
           onTurnPage(1);
@@ -258,7 +267,7 @@ class PaintablePages extends StatelessWidget {
       child: LayoutBuilder(
         builder: (context, constraints) {
           final maxSize = Size(constraints.maxWidth, constraints.maxHeight);
-          final pageSizeScaled = pages.calcCurrentPageSizeScaled(maxSize);
+          final (pageSizeScaled, _) = pages.calcPageSizesScaled(maxSize);
           return DrawingBoard(
             background: SizedBox(
               width: pageSizeScaled.width,
@@ -328,7 +337,7 @@ class Pages extends StatelessWidget {
             child: Stack(
               children: [
                 PdfPageView(
-                  key: ValueKey(currentPageNumber),
+                  key: ValueKey(currentPageNumber + 1),
                   document: document,
                   pageNumber: currentPageNumber + 1,
                   maximumDpi: 300,
@@ -350,12 +359,37 @@ class Pages extends StatelessWidget {
     );
   }
 
-  Size calcCurrentPageSizeScaled(Size parentSize) {
-    return _calcScaledPageSize(parentSize, _getCurrentPageSizeUnscaled());
+  (Size, Size?) calcPageSizesScaled(Size parentSize) {
+    if (config.twoPageMode) {
+      Size leftPageSizeUnscaled = _getPageSizeUnscaled(currentPageNumber);
+      Size rightPageSizeUnscaled = _getPageSizeUnscaled(currentPageNumber + 1);
+      Size combinedPageSizesUnscaled = Size(
+        leftPageSizeUnscaled.width + rightPageSizeUnscaled.width,
+        max(leftPageSizeUnscaled.height, rightPageSizeUnscaled.height),
+      );
+      Size combinedPageSizesScaled = _calcScaledPageSize(
+        parentSize,
+        combinedPageSizesUnscaled,
+      );
+      double scaleFactor =
+          combinedPageSizesScaled.width / combinedPageSizesUnscaled.width;
+      return (
+        leftPageSizeUnscaled * scaleFactor,
+        rightPageSizeUnscaled * scaleFactor,
+      );
+    } else {
+      return (
+        _calcScaledPageSize(
+          parentSize,
+          _getPageSizeUnscaled(currentPageNumber),
+        ),
+        null,
+      );
+    }
   }
 
-  Size _getCurrentPageSizeUnscaled() {
-    return document.pages.elementAt(currentPageNumber).size;
+  Size _getPageSizeUnscaled(int pageNumber) {
+    return document.pages.elementAt(pageNumber).size;
   }
 
   Size _calcScaledPageSize(Size parentSize, Size pageSize) {