Add offsetFromOrigin and localOffsetFromOrigin to DragUpdateDetails similar to LongPressMoveUpdateDetails, eliminates the need to hold the state of lastDragStartDetails

Author: Renzo Olivares

packages/flutter/lib/src/gestures/drag_details.dart

@@ -140,13 +140,17 @@ class DragUpdateDetails {
     this.primaryDelta,
     required this.globalPosition,
     Offset? localPosition,
+    this.offsetFromOrigin = Offset.zero,
+    Offset? localOffsetFromOrigin,
   }) : assert(delta != null),
        assert(
          primaryDelta == null
            || (primaryDelta == delta.dx && delta.dy == 0.0)
            || (primaryDelta == delta.dy && delta.dx == 0.0),
        ),
-       localPosition = localPosition ?? globalPosition;
+       assert(offsetFromOrigin != null),
+       localPosition = localPosition ?? globalPosition,
+       localOffsetFromOrigin = localOffsetFromOrigin ?? offsetFromOrigin;
 
   /// Recorded timestamp of the source pointer event that triggered the drag
   /// event.
@@ -191,6 +195,16 @@ class DragUpdateDetails {
   /// Defaults to [globalPosition] if not specified in the constructor.
   final Offset localPosition;
 
+  /// A delta offset from the point where the drag initially contacted
+  /// the screen to the point where the pointer is currently located (the
+  /// present [globalPosition]) when this callback is triggered.
+  final Offset offsetFromOrigin;
+
+  /// A local delta offset from the point where the drag initially contacted
+  /// the screen to the point where the pointer is currently located (the
+  /// present [localPosition]) when this callback is triggered.
+  final Offset localOffsetFromOrigin;
+
   @override
   String toString() => '${objectRuntimeType(this, 'DragUpdateDetails')}($delta)';
 }

packages/flutter/lib/src/gestures/monodrag.dart

@@ -479,6 +479,8 @@ abstract class DragGestureRecognizer extends OneSequenceGestureRecognizer {
         primaryDelta: primaryDelta,
         globalPosition: globalPosition,
         localPosition: localPosition,
+        offsetFromOrigin: globalPosition - _initialPosition.global,
+        localOffsetFromOrigin: localPosition! - _initialPosition.local,
       );
       invokeCallback<void>('onUpdate', () => onUpdate!(details));
     }

packages/flutter/lib/src/gestures/tap_and_drag.dart

@@ -42,6 +42,8 @@ class TapAndDragGestureRecognizer extends OneSequenceGestureRecognizer {
 
   GestureTapAndDragCancelCallback? onCancel;
 
+  // Drag related state
+  late OffsetPair _initialPosition;
   _DragState _state = _DragState.ready;
 
   // For consecutive tap
@@ -123,11 +125,14 @@ class TapAndDragGestureRecognizer extends OneSequenceGestureRecognizer {
           primaryDelta: null,
           globalPosition: event.position,
           localPosition: event.localPosition,
+          offsetFromOrigin: event.position - _initialPosition.global,
+          localOffsetFromOrigin: event.localPosition - _initialPosition.local,
         );
         invokeCallback<void>('onUpdate', () => onUpdate!(details, _dragTapCount!));
       } else if (_state == _DragState.possible) {
         print('is zoom start ${event is PointerPanZoomStartEvent}');
         _state = _DragState.accepted;
+        _initialPosition = OffsetPair(global: event.position, local: event.localPosition);
         DragStartDetails details = DragStartDetails(
           sourceTimeStamp: event.timeStamp,
           globalPosition: event.position,

packages/flutter/lib/src/widgets/text_selection.dart

@@ -32,19 +32,6 @@ export 'package:flutter/services.dart' show TextSelectionDelegate;
 /// called.
 const Duration _kDragSelectionUpdateThrottle = Duration(milliseconds: 50);
 
-/// Signature for when a pointer that's dragging to select text has moved again.
-///
-/// The first argument [startDetails] contains the details of the event that
-/// initiated the dragging.
-///
-/// The second argument [updateDetails] contains the details of the current
-/// pointer movement. It's the same as the one passed to [DragGestureRecognizer.onUpdate].
-///
-/// This signature is different from [GestureDragUpdateCallback] to make it
-/// easier for various text fields to use [TextSelectionGestureDetector] without
-/// having to store the start position.
-typedef DragSelectionUpdateCallback = void Function(DragStartDetails startDetails, DragUpdateDetails updateDetails, int tapCount);
-
 /// The type for a Function that builds a toolbar's container with the given
 /// child.
 ///
@@ -2115,7 +2102,7 @@ class TextSelectionGestureDetectorBuilder {
   ///  * [TextSelectionGestureDetector.onDragSelectionUpdate], which triggers
   ///    this callback./lib/src/material/text_field.dart
   @protected
-  void onDragSelectionUpdate(DragStartDetails startDetails, DragUpdateDetails updateDetails, int tapCount) {
+  void onDragSelectionUpdate(DragUpdateDetails details, int tapCount) {
     if (!delegate.selectionEnabled) {
       return;
     }
@@ -2125,32 +2112,33 @@ class TextSelectionGestureDetectorBuilder {
       final Offset startOffset = renderEditable.maxLines == 1
           ? Offset(renderEditable.offset.pixels - _dragStartViewportOffset, 0.0)
           : Offset(0.0, renderEditable.offset.pixels - _dragStartViewportOffset);
+      final Offset dragStartGlobalPosition = details.globalPosition - details.offsetFromOrigin;
 
       // Select word by word.
       if (tapCount == 2) {
         return renderEditable.selectWordsInRange(
-          from: startDetails.globalPosition - startOffset,
-          to: updateDetails.globalPosition,
+          from: dragStartGlobalPosition - startOffset,
+          to: details.globalPosition,
           cause: SelectionChangedCause.drag,
         );
       }
       return renderEditable.selectPositionAt(
-        from: startDetails.globalPosition - startOffset,
-        to: updateDetails.globalPosition,
+        from: dragStartGlobalPosition - startOffset,
+        to: details.globalPosition,
         cause: SelectionChangedCause.drag,
       );
     }
 
     if (_shiftTapDragSelection!.isCollapsed
         || (defaultTargetPlatform != TargetPlatform.iOS
             && defaultTargetPlatform != TargetPlatform.macOS)) {
-      return _extendSelection(updateDetails.globalPosition, SelectionChangedCause.drag);
+      return _extendSelection(details.globalPosition, SelectionChangedCause.drag);
     }
 
     // If the drag inverts the selection, Mac and iOS revert to the initial
     // selection.
     final TextSelection selection = editableText.textEditingValue.selection;
-    final TextPosition nextExtent = renderEditable.getPositionForPoint(updateDetails.globalPosition);
+    final TextPosition nextExtent = renderEditable.getPositionForPoint(details.globalPosition);
     final bool isShiftTapDragSelectionForward =
         _shiftTapDragSelection!.baseOffset < _shiftTapDragSelection!.extentOffset;
     final bool isInverted = isShiftTapDragSelectionForward
@@ -2179,7 +2167,7 @@ class TextSelectionGestureDetectorBuilder {
         SelectionChangedCause.drag,
       );
     } else {
-      _extendSelection(updateDetails.globalPosition, SelectionChangedCause.drag);
+      _extendSelection(details.globalPosition, SelectionChangedCause.drag);
     }
   }
 
@@ -2321,7 +2309,7 @@ class TextSelectionGestureDetector extends StatefulWidget {
   /// The frequency of calls is throttled to avoid excessive text layout
   /// operations in text fields. The throttling is controlled by the constant
   /// [_kDragSelectionUpdateThrottle].
-  final DragSelectionUpdateCallback? onDragSelectionUpdate;
+  final GestureTapAndDragUpdateCallback? onDragSelectionUpdate;
 
   /// Called when a mouse that was previously dragging is released.
   final GestureDragEndCallback? onDragSelectionEnd;
@@ -2376,17 +2364,13 @@ class _TextSelectionGestureDetectorState extends State<TextSelectionGestureDetec
     widget.onSingleTapCancel?.call();
   }
 
-  DragStartDetails? _lastDragStartDetails;
   DragUpdateDetails? _lastDragUpdateDetails;
   Timer? _dragUpdateThrottleTimer;
   int? _dragTapCount;
 
   void _handleDragStart(DragStartDetails details, int tapCount) {
     print('drag start');
-    assert(_lastDragStartDetails == null);
-    print('passed assert');
     print('tap count $tapCount');
-    _lastDragStartDetails = details;
     if (tapCount != 2) {
       widget.onDragSelectionStart?.call(details);
     }
@@ -2408,15 +2392,13 @@ class _TextSelectionGestureDetectorState extends State<TextSelectionGestureDetec
   /// Once the drag gesture ends, any pending drag update will be fired
   /// immediately. See [_handleDragEnd].
   void _handleDragUpdateThrottled() {
-    assert(_lastDragStartDetails != null);
     assert(_lastDragUpdateDetails != null);
-    widget.onDragSelectionUpdate?.call(_lastDragStartDetails!, _lastDragUpdateDetails!, _dragTapCount!);
+    widget.onDragSelectionUpdate?.call(_lastDragUpdateDetails!, _dragTapCount!);
     _dragUpdateThrottleTimer = null;
     _lastDragUpdateDetails = null;
   }
 
   void _handleDragEnd(TapUpDetails upDetails, DragEndDetails endDetails, int tapCount) {
-    assert(_lastDragStartDetails != null);
     print('drag end');
     print('tap count $tapCount');
     _handleTapUp(upDetails, tapCount);
@@ -2429,7 +2411,6 @@ class _TextSelectionGestureDetectorState extends State<TextSelectionGestureDetec
     widget.onDragSelectionEnd?.call(endDetails);
     _dragTapCount = null;
     _dragUpdateThrottleTimer = null;
-    _lastDragStartDetails = null;
     _lastDragUpdateDetails = null;
   }