Fix: PgUp/Dn, arrow scroll, Up arrow with large fonts, assert at start of text for indent

lib/src/widgets/editor/editor.dart

@@ -1384,6 +1384,13 @@ class RenderEditor extends RenderEditableContainerBox
     );
   }
 
+  /// Returns the TextPosition after moving by the vertical offset.
+  TextPosition getTextPositionMoveVertical(
+      TextPosition position, double verticalOffset) {
+    final caretOfs = localToGlobal(_getOffsetForCaret(position));
+    return getPositionForOffset(caretOfs.translate(0, verticalOffset));
+  }
+
   /// Returns the TextPosition above the given offset into the text.
   ///
   /// If the offset is already on the first line, the offset of the first
@@ -1434,11 +1441,10 @@ class RenderEditor extends RenderEditableContainerBox
     var newPosition = child.getPositionBelow(localPosition);
 
     if (newPosition == null) {
-      // There was no text above in the current child, check the direct
-      // sibling.
+      // There was no text below in the current child, check the direct sibling.
       final sibling = childAfter(child);
       if (sibling == null) {
-        // reached beginning of the document, move to the
+        // reached end of the document, move to the
         // last character
         newPosition = TextPosition(offset: document.length - 1);
       } else {
@@ -1501,6 +1507,11 @@ class QuillVerticalCaretMovementRun implements Iterator<TextPosition> {
     _currentTextPosition = _editor.getTextPositionAbove(_currentTextPosition);
     return true;
   }
+
+  void moveVertical(double verticalOffset) {
+    _currentTextPosition = _editor.getTextPositionMoveVertical(
+        _currentTextPosition, verticalOffset);
+  }
 }
 
 class EditableContainerParentData
@@ -1568,7 +1579,6 @@ class RenderEditableContainerBox extends RenderBox
 
   RenderEditableBox childAtPosition(TextPosition position) {
     assert(firstChild != null);
-
     final targetNode = container.queryChild(position.offset, false).node;
 
     var targetChild = firstChild;
@@ -1578,6 +1588,8 @@ class RenderEditableContainerBox extends RenderBox
       }
       final newChild = childAfter(targetChild);
       if (newChild == null) {
+        //  At start of document fails to find the position
+        targetChild = childAtOffset(const Offset(0, 0));
         break;
       }
       targetChild = newChild;

lib/src/widgets/quill/text_block.dart

@@ -691,7 +691,7 @@ class RenderEditableTextBlock extends RenderEditableContainerBox
 
   @override
   TextPosition globalToLocalPosition(TextPosition position) {
-    assert(container.containsOffset(position.offset) || container.length == 0,
+    assert(container.containsOffset(position.offset),
         'The provided text position is not in the current node');
     return TextPosition(
       offset: position.offset - container.documentOffset,

lib/src/widgets/quill/text_line.dart

@@ -922,10 +922,10 @@ class RenderEditableTextLine extends RenderEditableBox {
   @override
   TextPosition? getPositionAbove(TextPosition position) {
     /// Move up by fraction of the default font height, larger font sizes need larger offset
-    for ( var offset = -0.5; ; offset -= 0.25 ) {
+    for (var offset = -0.5;; offset -= 0.25) {
       final pos = _getPosition(position, offset);
-      if ( pos != position || offset <= -2.0 ) {
-        return  pos;
+      if (pos != position || offset <= -2.0) {
+        return pos;
       }
     }
   }

lib/src/widgets/raw_editor/raw_editor_actions.dart

@@ -607,3 +607,97 @@ class NavigateToDocumentBoundaryAction
     );
   }
 }
+
+/// An [Action] that scrolls the Quill editor scroll bar by the amount configured
+/// in the [ScrollIntent] given to it.
+///
+/// The default for a [ScrollIntent.type] set to [ScrollIncrementType.page] is 80% of the
+/// size of the scroll window, and for [ScrollIncrementType.line], 50 logical pixels.
+/// Modelled on 'class ScrollAction' in flutter's scrollable_helpers.dart
+class QuillEditorScrollAction extends ContextAction<ScrollIntent> {
+  QuillEditorScrollAction(this.state);
+
+  final QuillRawEditorState state;
+
+  @override
+  void invoke(ScrollIntent intent, [BuildContext? context]) {
+    final sc = state.scrollController;
+    final increment = switch (intent.type) {
+      ScrollIncrementType.line => 50.0,
+      ScrollIncrementType.page => 0.8 * sc.position.viewportDimension,
+    };
+    sc.position.moveTo(
+      sc.position.pixels +
+          (intent.direction == AxisDirection.down ? increment : -increment),
+      duration: const Duration(milliseconds: 100),
+      curve: Curves.easeInOut,
+    );
+  }
+}
+
+/// An [Action] that moves the caret by a page.
+///
+/// The default movement is 80% of the size of the scroll window.
+/// Modelled on 'class _UpdateTextSelectionVerticallyAction' in flutter's editable_text.dart
+class QuillEditorUpdateTextSelectionToAdjacentPageAction<
+    T extends DirectionalCaretMovementIntent> extends ContextAction<T> {
+  QuillEditorUpdateTextSelectionToAdjacentPageAction(this.state);
+
+  final QuillRawEditorState state;
+
+  QuillVerticalCaretMovementRun? _verticalMovementRun;
+  TextSelection? _runSelection;
+
+  void stopCurrentVerticalRunIfSelectionChanges() {
+    final runSelection = _runSelection;
+    if (runSelection == null) {
+      assert(_verticalMovementRun == null);
+      return;
+    }
+    _runSelection = state.textEditingValue.selection;
+    final currentSelection = state.controller.selection;
+    final continueCurrentRun = currentSelection.isValid &&
+        currentSelection.isCollapsed &&
+        currentSelection.baseOffset == runSelection.baseOffset &&
+        currentSelection.extentOffset == runSelection.extentOffset;
+    if (!continueCurrentRun) {
+      _verticalMovementRun = null;
+      _runSelection = null;
+    }
+  }
+
+  @override
+  void invoke(T intent, [BuildContext? context]) {
+    assert(state.textEditingValue.selection.isValid);
+
+    final collapseSelection = intent.collapseSelection ||
+        !state.widget.configurations.selectionEnabled;
+    final value = state.textEditingValue;
+    if (!value.selection.isValid) {
+      return;
+    }
+
+    final currentRun = state.renderEditor
+        .startVerticalCaretMovement(state.renderEditor.selection.extent);
+
+    final pageOffset = 0.8 * state.scrollController.position.viewportDimension;
+    currentRun.moveVertical(intent.forward ? pageOffset : -pageOffset);
+    final newExtent = currentRun.current;
+    final newSelection = collapseSelection
+        ? TextSelection.fromPosition(newExtent)
+        : value.selection.extendTo(newExtent);
+
+    Actions.invoke(
+      context!,
+      UpdateSelectionIntent(
+          value, newSelection, SelectionChangedCause.keyboard),
+    );
+    if (state.textEditingValue.selection == newSelection) {
+      _verticalMovementRun = currentRun;
+      _runSelection = newSelection;
+    }
+  }
+
+  @override
+  bool get isActionEnabled => state.textEditingValue.selection.isValid;
+}

lib/src/widgets/raw_editor/raw_editor_state.dart

@@ -713,6 +713,30 @@ class QuillRawEditorState extends EditorState
               control: !isDesktopMacOS,
               meta: isDesktopMacOS,
             ): const ScrollToDocumentBoundaryIntent(forward: true),
+
+            //  Arrow key scrolling
+            SingleActivator(
+              LogicalKeyboardKey.arrowUp,
+              control: !isDesktopMacOS,
+              meta: isDesktopMacOS,
+            ): const ScrollIntent(direction: AxisDirection.up),
+            SingleActivator(
+              LogicalKeyboardKey.arrowDown,
+              control: !isDesktopMacOS,
+              meta: isDesktopMacOS,
+            ): const ScrollIntent(direction: AxisDirection.down),
+            SingleActivator(
+              LogicalKeyboardKey.pageUp,
+              control: !isDesktopMacOS,
+              meta: isDesktopMacOS,
+            ): const ScrollIntent(
+                direction: AxisDirection.up, type: ScrollIncrementType.page),
+            SingleActivator(
+              LogicalKeyboardKey.pageDown,
+              control: !isDesktopMacOS,
+              meta: isDesktopMacOS,
+            ): const ScrollIntent(
+                direction: AxisDirection.down, type: ScrollIncrementType.page),
           }, {
             ...?widget.configurations.customShortcuts
           }),
@@ -1622,6 +1646,10 @@ class QuillRawEditorState extends EditorState
       QuillEditorUpdateTextSelectionToAdjacentLineAction<
           ExtendSelectionVerticallyToAdjacentLineIntent>(this);
 
+  late final _adjacentPageAction =
+      QuillEditorUpdateTextSelectionToAdjacentPageAction<
+          ExtendSelectionVerticallyToAdjacentPageIntent>(this);
+
   late final QuillEditorToggleTextStyleAction _formatSelectionAction =
       QuillEditorToggleTextStyleAction(this);
 
@@ -1695,7 +1723,12 @@ class QuillRawEditorState extends EditorState
     QuillEditorApplyHeaderIntent: _applyHeaderAction,
     QuillEditorApplyCheckListIntent: _applyCheckListAction,
     QuillEditorApplyLinkIntent: QuillEditorApplyLinkAction(this),
-    ScrollToDocumentBoundaryIntent: NavigateToDocumentBoundaryAction(this)
+    ScrollToDocumentBoundaryIntent: NavigateToDocumentBoundaryAction(this),
+
+    //  Paging and scrolling
+    ExtendSelectionVerticallyToAdjacentPageIntent:
+        _makeOverridable(_adjacentPageAction),
+    ScrollIntent: QuillEditorScrollAction(this),
   };
 
   @override