[SuperEditor][Android] Fix auto-scrolling start region (Resolves #2000)…

… (#2036)

super_editor/lib/src/default_editor/document_gestures_touch_android.dart

@@ -1388,6 +1388,18 @@ class SuperEditorAndroidControlsOverlayManagerState extends State<SuperEditorAnd
   @visibleForTesting
   bool get wantsToDisplayMagnifier => _controlsController!.shouldShowMagnifier.value;
 
+  /// Returns the `RenderBox` for the scrolling viewport.
+  ///
+  /// If this widget has an ancestor `Scrollable`, then the returned
+  /// `RenderBox` belongs to that ancestor `Scrollable`.
+  ///
+  /// If this widget doesn't have an ancestor `Scrollable`, then this
+  /// widget includes a `ScrollView` and this `State`'s render object
+  /// is the viewport `RenderBox`.
+  RenderBox get viewportBox =>
+      (context.findAncestorScrollableWithVerticalScroll?.context.findRenderObject() ?? context.findRenderObject())
+          as RenderBox;
+
   void _onSelectionChange() {
     final selection = widget.selection.value;
     if (selection == null) {
@@ -1547,11 +1559,12 @@ class SuperEditorAndroidControlsOverlayManagerState extends State<SuperEditorAnd
       documentLayout.getDocumentOffsetFromAncestorOffset(_dragHandleSelectionGlobalFocalPoint.value!),
     )!;
 
+    final centerOfContentInContentSpace = documentLayout.getRectForPosition(nearestPosition)!.center;
+
     // Move the magnifier focal point to match the drag x-offset, but always remain focused on the vertical
     // center of the line.
-    final centerOfContentAtNearestPosition = documentLayout.getAncestorOffsetFromDocumentOffset(
-      documentLayout.getRectForPosition(nearestPosition)!.center,
-    );
+    final centerOfContentAtNearestPosition =
+        documentLayout.getAncestorOffsetFromDocumentOffset(centerOfContentInContentSpace);
     _magnifierFocalPoint.value = Offset(
       _magnifierFocalPoint.value!.dx + dragDx,
       centerOfContentAtNearestPosition.dy,
@@ -1581,10 +1594,17 @@ class SuperEditorAndroidControlsOverlayManagerState extends State<SuperEditorAnd
     // Update the auto-scroll focal point so that the viewport scrolls if we're
     // close to the boundary.
     widget.dragHandleAutoScroller.value?.updateAutoScrollHandleMonitoring(
-      dragEndInViewport: centerOfContentAtNearestPosition,
+      dragEndInViewport: _contentOffsetInViewport(centerOfContentInContentSpace),
     );
   }
 
+  /// Converts the [offset] in content space to an offset in the viewport space.
+  Offset _contentOffsetInViewport(Offset offset) {
+    final documentLayout = widget.getDocumentLayout();
+    final globalOffset = documentLayout.getGlobalOffsetFromDocumentOffset(offset);
+    return viewportBox.globalToLocal(globalOffset);
+  }
+
   @override
   Widget build(BuildContext context) {
     return OverlayPortal(

super_editor/test/super_editor/supereditor_scrolling_test.dart

@@ -201,6 +201,54 @@ void main() {
       );
     });
 
+    testWidgetsOnMobile('starts auto-scrolling when dragging near the top', (tester) async {
+      final scrollController = ScrollController();
+
+      // Pump an editor with an appbar above the editor so we make sure that
+      // auto-scroll starts when the user dragged near the top of the editor,
+      // not at the top of the screen.
+      await tester
+          .createDocument()
+          .withLongTextContent()
+          .withScrollController(scrollController)
+          .withEditorSize(Size(300, 300))
+          .autoFocus(true)
+          .withAppBar(100.0)
+          .pump();
+
+      // Scroll all the way to the bottom.
+      scrollController.jumpTo(scrollController.position.maxScrollExtent);
+      await tester.pumpAndSettle();
+
+      // Place the caret at approximately at the middle of the first visible line.
+      await tester.tapAt(tester.getTopLeft(find.byType(SuperEditor)) + Offset(150, 20));
+      await tester.pump(kDoubleTapTimeout);
+
+      final scrollOffsetBeforeDrag = scrollController.offset;
+
+      // Drag the handle a bit to the top.
+      final dragGesture = await tester.startGesture(tester.getCenter(
+        SuperEditorInspector.findMobileCaretDragHandle(),
+      ));
+      await dragGesture.moveBy(Offset(0, -20));
+      await tester.pump();
+
+      // Pump some frames to let the auto-scroll kick in.
+      for (int i = 0; i < 60; i += 1) {
+        await tester.pump();
+      }
+
+      // Release the gesture.
+      await dragGesture.up();
+      await tester.pump();
+
+      // Ensure the editor scrolled up.
+      expect(scrollController.offset, lessThan(scrollOffsetBeforeDrag));
+
+      // Let the long-press timer resolve.
+      await tester.pump(kLongPressTimeout);
+    });
+
     testWidgetsOnDesktop("auto-scrolls to caret position", (tester) async {
       const windowSize = Size(800, 600);
       tester.view.physicalSize = windowSize;

super_editor/test/super_editor/supereditor_test_tools.dart

@@ -262,6 +262,14 @@ class TestSuperEditorConfigurator {
     return this;
   }
 
+  /// Configures the [SuperEditor] to display an [AppBar] with the given height above the [SuperEditor].
+  ///
+  /// If [withCustomWidgetTreeBuilder] is used, this setting is ignored.
+  TestSuperEditorConfigurator withAppBar(double height) {
+    _config.appBarHeight = height;
+    return this;
+  }
+
   /// Configures the [SuperEditor] to use the given [scrollController]
   TestSuperEditorConfigurator withScrollController(ScrollController? scrollController) {
     _config.scrollController = scrollController;
@@ -438,6 +446,17 @@ class TestSuperEditorConfigurator {
       // Flutter to pick the web shortcuts.
       shortcuts: defaultFlutterShortcuts,
       home: Scaffold(
+        appBar: _config.appBarHeight != null
+            ? PreferredSize(
+                preferredSize: ui.Size(double.infinity, _config.appBarHeight!),
+                child: SafeArea(
+                  child: SizedBox(
+                    height: _config.appBarHeight!,
+                    child: ColoredBox(color: Colors.yellow),
+                  ),
+                ),
+              )
+            : null,
         body: superEditor,
       ),
       debugShowCheckedModeBanner: false,
@@ -674,6 +693,7 @@ class SuperEditorTestConfiguration {
   final plugins = <SuperEditorPlugin>{};
 
   WidgetTreeBuilder? widgetTreeBuilder;
+  double? appBarHeight;
 }
 
 /// Must return a widget tree containing the given [superEditor]