Add optional two page mode

lib/sheet_viewer_page.dart

@@ -26,6 +26,7 @@ class _SheetViewerPageState extends State<SheetViewerPage> {
   bool isFullscreen = false;
   late Future<bool> documentLoaded;
   PdfDocument? document;
+  bool twoPageMode = true;
 
   @override
   void initState() {
@@ -79,7 +80,21 @@ class _SheetViewerPageState extends State<SheetViewerPage> {
           if (snapshot.hasData && document != null) {
             numPages = document!.pages.length;
 
-            return GestureDetector(
+            return Stack(
+              children: [
+                Container(
+                  alignment: Alignment.bottomLeft,
+                  margin: EdgeInsets.all(10),
+                  child: FloatingActionButton(
+                    onPressed: () {
+                      setState(() {
+                        twoPageMode = !twoPageMode;
+                      });
+                    },
+                    child: Icon(twoPageMode ? Icons.filter_1 : Icons.filter_2),
+                  ),
+                ),
+                GestureDetector(
                   onTapUp: (TapUpDetails details) {
                     // Get the size of the screen
                     final screenWidth = MediaQuery.of(context).size.width;
@@ -123,14 +138,19 @@ class _SheetViewerPageState extends State<SheetViewerPage> {
                           ),
                         ],
                       ),
-                  // PdfPageView(
-                  //   key: ValueKey(page),
-                  //   document: document,
-                  //   pageNumber: page + 1,
-                  //   alignment: Alignment.center,
-                  // ),
+                      Visibility(
+                        visible: twoPageMode == true,
+                        child: PdfPageView(
+                          key: ValueKey(page),
+                          document: document,
+                          pageNumber: page + 1,
+                          alignment: Alignment.center,
+                        ),
+                      ),
                     ],
                   ),
+                ),
+              ],
             );
           } else if (snapshot.hasError) {
             return Center(