Visibility of text selection handlers

packages/zefyr/lib/src/rendering/editor.dart

@@ -97,6 +97,7 @@ abstract class RenderAbstractEditor {
 class RenderEditor extends RenderEditableContainerBox
     implements RenderAbstractEditor {
   RenderEditor({
+    ViewportOffset? offset,
     List<RenderEditableBox>? children,
     required NotusDocument document,
     required TextDirection textDirection,
@@ -143,6 +144,19 @@ class RenderEditor extends RenderEditableContainerBox
     markNeedsSemanticsUpdate();
   }
 
+  Offset get _paintOffset => Offset(0.0, -(offset?.pixels ?? 0.0));
+
+  ViewportOffset? get offset => _offset;
+  ViewportOffset? _offset;
+
+  set offset(ViewportOffset? value) {
+    if (_offset == value) return;
+    if (attached) _offset?.removeListener(markNeedsPaint);
+    _offset = value;
+    if (attached) _offset?.addListener(markNeedsPaint);
+    markNeedsLayout();
+  }
+
   /// The region of text that is selected, if any.
   ///
   /// The caret position is represented by a collapsed selection.
@@ -196,8 +210,6 @@ class RenderEditor extends RenderEditableContainerBox
   /// visible on the screen.
   ValueListenable<bool> get selectionStartInViewport =>
       _selectionStartInViewport;
-
-  // TODO: implement selectionStartInViewport
   final ValueNotifier<bool> _selectionStartInViewport =
       ValueNotifier<bool>(true);
 
@@ -211,10 +223,44 @@ class RenderEditor extends RenderEditableContainerBox
   /// This bool indicates whether the text is scrolled so that the handle is
   /// inside the text field viewport, as opposed to whether it is actually
   /// visible on the screen.
-  // TODO: implement selectionEndInViewport
   ValueListenable<bool> get selectionEndInViewport => _selectionEndInViewport;
   final ValueNotifier<bool> _selectionEndInViewport = ValueNotifier<bool>(true);
 
+  void _updateSelectionExtentsVisibility(Offset effectiveOffset) {
+    final visibleRegion = Offset.zero & size;
+    final startPosition =
+        TextPosition(offset: selection.start, affinity: selection.affinity);
+    final startOffset = _getOffsetForCaret(startPosition);
+    // TODO(justinmc): https://github.com/flutter/flutter/issues/31495
+    // Check if the selection is visible with an approximation because a
+    // difference between rounded and unrounded values causes the caret to be
+    // reported as having a slightly (< 0.5) negative y offset. This rounding
+    // happens in paragraph.cc's layout and TextPainer's
+    // _applyFloatingPointHack. Ideally, the rounding mismatch will be fixed and
+    // this can be changed to be a strict check instead of an approximation.
+    const visibleRegionSlop = 0.5;
+    _selectionStartInViewport.value = visibleRegion
+        .inflate(visibleRegionSlop)
+        .contains(startOffset + effectiveOffset);
+
+    final endPosition =
+        TextPosition(offset: selection.end, affinity: selection.affinity);
+    final endOffset = _getOffsetForCaret(endPosition);
+    _selectionEndInViewport.value = visibleRegion
+        .inflate(visibleRegionSlop)
+        .contains(endOffset + effectiveOffset);
+  }
+
+  // returns offset relative to this at which the caret will be painted
+  // given a global TextPosition
+  Offset _getOffsetForCaret(TextPosition position) {
+    final child = childAtPosition(position);
+    final childPosition = child.globalToLocalPosition(position);
+    final boxParentData = child.parentData as BoxParentData;
+    final localOffsetForCaret = child.getOffsetForCaret(childPosition);
+    return boxParentData.offset + localOffsetForCaret;
+  }
+
   /// Finds the closest scroll offset that fully reveals the editing cursor.
   ///
   /// The `scrollOffset` parameter represents current scroll offset in the
@@ -513,6 +559,7 @@ class RenderEditor extends RenderEditableContainerBox
   @override
   void paint(PaintingContext context, Offset offset) {
     defaultPaint(context, offset);
+    _updateSelectionExtentsVisibility(offset + _paintOffset);
     _paintHandleLayers(context, getEndpointsForSelection(selection));
   }
 

packages/zefyr/lib/src/widgets/editor.dart

@@ -8,6 +8,7 @@ import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
 import 'package:notus/notus.dart';
 import 'package:zefyr/src/widgets/baseline_proxy.dart';
+import 'package:zefyr/src/widgets/single_child_scroll_view.dart';
 
 import '../rendering/editor.dart';
 import '../services/keyboard.dart';
@@ -1111,10 +1112,25 @@ class RawEditorState extends EditorState
       child = BaselineProxy(
         textStyle: _themeData.paragraph.style,
         padding: baselinePadding,
-        child: SingleChildScrollView(
+        child: ZefyrSingleChildScrollView(
           controller: _scrollController,
           physics: widget.scrollPhysics,
-          child: child,
+          viewportBuilder: (_, offset) => CompositedTransformTarget(
+            link: _toolbarLayerLink,
+            child: _Editor(
+              key: _editorKey,
+              offset: offset,
+              document: widget.controller.document,
+              selection: widget.controller.selection,
+              hasFocus: _hasFocus,
+              textDirection: _textDirection,
+              startHandleLayerLink: _startHandleLayerLink,
+              endHandleLayerLink: _endHandleLayerLink,
+              onSelectionChanged: _handleSelectionChanged,
+              padding: widget.padding,
+              children: _buildChildren(context),
+            ),
+          ),
         ),
       );
     }
@@ -1210,6 +1226,7 @@ class _Editor extends MultiChildRenderObjectWidget {
   _Editor({
     required Key key,
     required List<Widget> children,
+    this.offset,
     required this.document,
     required this.textDirection,
     required this.hasFocus,
@@ -1220,6 +1237,7 @@ class _Editor extends MultiChildRenderObjectWidget {
     this.padding = EdgeInsets.zero,
   }) : super(key: key, children: children);
 
+  final ViewportOffset? offset;
   final NotusDocument document;
   final TextDirection textDirection;
   final bool hasFocus;
@@ -1232,6 +1250,7 @@ class _Editor extends MultiChildRenderObjectWidget {
   @override
   RenderEditor createRenderObject(BuildContext context) {
     return RenderEditor(
+      offset: offset,
       document: document,
       textDirection: textDirection,
       hasFocus: hasFocus,
@@ -1246,6 +1265,7 @@ class _Editor extends MultiChildRenderObjectWidget {
   @override
   void updateRenderObject(
       BuildContext context, covariant RenderEditor renderObject) {
+    renderObject.offset = offset;
     renderObject.document = document;
     renderObject.node = document.root;
     renderObject.textDirection = textDirection;