Refactor OverlayPortal semantics (flutter#173005)

Fixes flutter#163576
Fixes flutter#175184

This PR refactored the grafting part on `OverlayPortal`. Originally, the
semantics tree of `OverlayPortal` was constructed/grafted in render
object phase to make sure the correctness of the traversal order.
However this resulted wrong hit-test order and the issue surfaced on
web. With the fact that on web we are not able to graft/correct hit-test
order tree, this PR:
* Reverts the original grafting of the `OverlayPortal` so the hit-test
order is always correct.
* Then, we adds the grafting and updates the traversal order when we
send `childrenInTraversalOrder` to engine.
* Updating `childrenInTraversalOrder` causes it have different length
from the length of `childrenInHitTestOrder` and wrong hit-test transform
of the `OverlayPortal` children because when the transform is
calculated, it assumes a correct traversal order. To fix these issues,
this PR also:
  * recalculates the transform for `OverlayPortal` children.
  * adds `hitTestTransform` property and pass it to Android engine.
* skip grafting for web because it assumes the same length of
`childrenInTraversalOrder` and `childrenInHitTestOrder`.
* added grafting by using `ARIA-owns` in web engine to fix the traversal
order.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

Author: QuncCccccc

engine/src/flutter/lib/ui/fixtures/ui_test.dart

@@ -176,6 +176,7 @@ void sendSemanticsUpdate() {
   String tooltip = "tooltip";
 
   final Float64List transform = Float64List(16);
+  final Float64List hitTestTransform = Float64List(16);
   final Int32List childrenInTraversalOrder = Int32List(0);
   final Int32List childrenInHitTestOrder = Int32List(0);
   final Int32List additionalActions = Int32List(0);
@@ -198,6 +199,26 @@ void sendSemanticsUpdate() {
   transform[13] = 0;
   transform[14] = 0;
   transform[15] = 0;
+
+  hitTestTransform[0] = 1;
+  hitTestTransform[1] = 0;
+  hitTestTransform[2] = 0;
+  hitTestTransform[3] = 0;
+
+  hitTestTransform[4] = 0;
+  hitTestTransform[5] = 1;
+  hitTestTransform[6] = 0;
+  hitTestTransform[7] = 0;
+
+  hitTestTransform[8] = 0;
+  hitTestTransform[9] = 0;
+  hitTestTransform[10] = 1;
+  hitTestTransform[11] = 0;
+
+  hitTestTransform[12] = 0;
+  hitTestTransform[13] = 0;
+  hitTestTransform[14] = 0;
+  hitTestTransform[15] = 0;
   builder.updateNode(
     id: 0,
     flags: SemanticsFlags.none,
@@ -209,6 +230,7 @@ void sendSemanticsUpdate() {
     platformViewId: -1,
     scrollChildren: 0,
     scrollIndex: 0,
+    traversalParent: 0,
     scrollPosition: 0,
     scrollExtentMax: 0,
     scrollExtentMin: 0,
@@ -227,6 +249,7 @@ void sendSemanticsUpdate() {
     tooltip: tooltip,
     textDirection: TextDirection.ltr,
     transform: transform,
+    hitTestTransform: hitTestTransform,
     childrenInTraversalOrder: childrenInTraversalOrder,
     childrenInHitTestOrder: childrenInHitTestOrder,
     additionalActions: additionalActions,
@@ -244,13 +267,18 @@ void sendSemanticsUpdateWithRole() {
   final SemanticsUpdateBuilder builder = SemanticsUpdateBuilder();
 
   final Float64List transform = Float64List(16);
+  final Float64List hitTestTransform = Float64List(16);
   final Int32List childrenInTraversalOrder = Int32List(0);
   final Int32List childrenInHitTestOrder = Int32List(0);
   final Int32List additionalActions = Int32List(0);
   // Identity matrix 4x4.
   transform[0] = 1;
   transform[5] = 1;
   transform[10] = 1;
+
+  hitTestTransform[0] = 1;
+  hitTestTransform[5] = 1;
+  hitTestTransform[10] = 1;
   builder.updateNode(
     id: 0,
     flags: SemanticsFlags.none,
@@ -262,6 +290,7 @@ void sendSemanticsUpdateWithRole() {
     platformViewId: -1,
     scrollChildren: 0,
     scrollIndex: 0,
+    traversalParent: 0,
     scrollPosition: 0,
     scrollExtentMax: 0,
     scrollExtentMin: 0,
@@ -280,6 +309,7 @@ void sendSemanticsUpdateWithRole() {
     tooltip: "tooltip",
     textDirection: TextDirection.ltr,
     transform: transform,
+    hitTestTransform: hitTestTransform,
     childrenInTraversalOrder: childrenInTraversalOrder,
     childrenInHitTestOrder: childrenInHitTestOrder,
     additionalActions: additionalActions,
@@ -298,13 +328,18 @@ void sendSemanticsUpdateWithLocale() {
   final SemanticsUpdateBuilder builder = SemanticsUpdateBuilder();
 
   final Float64List transform = Float64List(16);
+  final Float64List hitTestTransform = Float64List(16);
   final Int32List childrenInTraversalOrder = Int32List(0);
   final Int32List childrenInHitTestOrder = Int32List(0);
   final Int32List additionalActions = Int32List(0);
   // Identity matrix 4x4.
   transform[0] = 1;
   transform[5] = 1;
   transform[10] = 1;
+
+  hitTestTransform[0] = 1;
+  hitTestTransform[5] = 1;
+  hitTestTransform[10] = 1;
   builder.updateNode(
     id: 0,
     flags: SemanticsFlags.none,
@@ -319,6 +354,7 @@ void sendSemanticsUpdateWithLocale() {
     scrollPosition: 0,
     scrollExtentMax: 0,
     scrollExtentMin: 0,
+    traversalParent: 0,
     rect: Rect.fromLTRB(0, 0, 10, 10),
     identifier: "identifier",
     label: "label",
@@ -334,6 +370,7 @@ void sendSemanticsUpdateWithLocale() {
     tooltip: "tooltip",
     textDirection: TextDirection.ltr,
     transform: transform,
+    hitTestTransform: hitTestTransform,
     childrenInTraversalOrder: childrenInTraversalOrder,
     childrenInHitTestOrder: childrenInHitTestOrder,
     additionalActions: additionalActions,
@@ -370,6 +407,7 @@ void sendSemanticsUpdateWithIsLink() {
     platformViewId: -1,
     scrollChildren: 0,
     scrollIndex: 0,
+    traversalParent: 0,
     scrollPosition: 0,
     scrollExtentMax: 0,
     scrollExtentMin: 0,
@@ -388,6 +426,7 @@ void sendSemanticsUpdateWithIsLink() {
     tooltip: "tooltip",
     textDirection: TextDirection.ltr,
     transform: transform,
+    hitTestTransform: transform,
     childrenInTraversalOrder: childrenInTraversalOrder,
     childrenInHitTestOrder: childrenInHitTestOrder,
     additionalActions: additionalActions,

engine/src/flutter/lib/ui/semantics.dart

@@ -1817,6 +1817,21 @@ abstract class SemanticsUpdateBuilder {
   /// total number of child nodes that contribute semantics and `scrollIndex`
   /// is the index of the first visible child node that contributes semantics.
   ///
+  /// The `traversalParent` specifies the ID of the semantics node that serves as
+  /// the logical parent of this node for accessibility traversal. This
+  /// parameter is only used by the web engine to establish parent-child
+  /// relationships between nodes that are not directly connected in paint order.
+  /// To ensure correct accessibility traversal, `traversalParent` should be set
+  /// to the logical traversal parent node ID. This parameter is web-specific
+  /// because other platforms can complete grafting when generating the
+  /// semantics tree in traversal order. After grafting, the traversal order and
+  /// hit-test order will be different, which is acceptable for other platforms.
+  /// However, the web engine assumes these two orders are exactly the same, so
+  /// grafting cannot be performed ahead of time on web. Instead, the traversal
+  /// order is updated in the web engine by setting the `aria-owns` attribute
+  /// through this parameter. A value of -1 indicates no special traversal
+  /// parent. This parameter has no effect on other platforms.
+  ///
   /// The `rect` is the region occupied by this node in its own coordinate
   /// system.
   ///
@@ -1875,6 +1890,7 @@ abstract class SemanticsUpdateBuilder {
     required int platformViewId,
     required int scrollChildren,
     required int scrollIndex,
+    required int traversalParent,
     required double scrollPosition,
     required double scrollExtentMax,
     required double scrollExtentMin,
@@ -1893,6 +1909,7 @@ abstract class SemanticsUpdateBuilder {
     required String tooltip,
     required TextDirection? textDirection,
     required Float64List transform,
+    required Float64List hitTestTransform,
     required Int32List childrenInTraversalOrder,
     required Int32List childrenInHitTestOrder,
     required Int32List additionalActions,
@@ -1954,6 +1971,7 @@ base class _NativeSemanticsUpdateBuilder extends NativeFieldWrapperClass1
     required int platformViewId,
     required int scrollChildren,
     required int scrollIndex,
+    required int traversalParent,
     required double scrollPosition,
     required double scrollExtentMax,
     required double scrollExtentMin,
@@ -1972,6 +1990,7 @@ base class _NativeSemanticsUpdateBuilder extends NativeFieldWrapperClass1
     required String tooltip,
     required TextDirection? textDirection,
     required Float64List transform,
+    required Float64List hitTestTransform,
     required Int32List childrenInTraversalOrder,
     required Int32List childrenInHitTestOrder,
     required Int32List additionalActions,
@@ -2000,6 +2019,7 @@ base class _NativeSemanticsUpdateBuilder extends NativeFieldWrapperClass1
       platformViewId,
       scrollChildren,
       scrollIndex,
+      traversalParent,
       scrollPosition,
       scrollExtentMax,
       scrollExtentMin,
@@ -2021,6 +2041,7 @@ base class _NativeSemanticsUpdateBuilder extends NativeFieldWrapperClass1
       tooltip,
       textDirection != null ? textDirection.index + 1 : 0,
       transform,
+      hitTestTransform,
       childrenInTraversalOrder,
       childrenInHitTestOrder,
       additionalActions,
@@ -2048,6 +2069,7 @@ base class _NativeSemanticsUpdateBuilder extends NativeFieldWrapperClass1
       Int32,
       Int32,
       Int32,
+      Int32,
       Double,
       Double,
       Double,
@@ -2072,6 +2094,7 @@ base class _NativeSemanticsUpdateBuilder extends NativeFieldWrapperClass1
       Handle,
       Handle,
       Handle,
+      Handle,
       Int32,
       Handle,
       Int32,
@@ -2093,6 +2116,7 @@ base class _NativeSemanticsUpdateBuilder extends NativeFieldWrapperClass1
     int platformViewId,
     int scrollChildren,
     int scrollIndex,
+    int traversalParent,
     double scrollPosition,
     double scrollExtentMax,
     double scrollExtentMin,
@@ -2114,6 +2138,7 @@ base class _NativeSemanticsUpdateBuilder extends NativeFieldWrapperClass1
     String tooltip,
     int textDirection,
     Float64List transform,
+    Float64List hitTestTransform,
     Int32List childrenInTraversalOrder,
     Int32List childrenInHitTestOrder,
     Int32List additionalActions,

engine/src/flutter/lib/ui/semantics/semantics_node.h

@@ -141,6 +141,7 @@ struct SemanticsNode {
   int32_t platformViewId = -1;
   int32_t scrollChildren = 0;
   int32_t scrollIndex = 0;
+  int32_t traversalParent = 0;
   double scrollPosition = std::nan("");
   double scrollExtentMax = std::nan("");
   double scrollExtentMin = std::nan("");
@@ -160,6 +161,7 @@ struct SemanticsNode {
 
   SkRect rect = SkRect::MakeEmpty();  // Local space, relative to parent.
   SkM44 transform = SkM44{};          // Identity
+  SkM44 hitTestTransform = SkM44{};   // Identity
   std::vector<int32_t> childrenInTraversalOrder;
   std::vector<int32_t> childrenInHitTestOrder;
   std::vector<int32_t> customAccessibilityActions;

engine/src/flutter/lib/ui/semantics/semantics_update_builder.cc

@@ -41,6 +41,7 @@ void SemanticsUpdateBuilder::updateNode(
     int platformViewId,
     int scrollChildren,
     int scrollIndex,
+    int traversalParent,
     double scrollPosition,
     double scrollExtentMax,
     double scrollExtentMin,
@@ -62,6 +63,7 @@ void SemanticsUpdateBuilder::updateNode(
     std::string tooltip,
     int textDirection,
     const tonic::Float64List& transform,
+    const tonic::Float64List& hitTestTransform,
     const tonic::Int32List& childrenInTraversalOrder,
     const tonic::Int32List& childrenInHitTestOrder,
     const tonic::Int32List& localContextActions,
@@ -90,6 +92,7 @@ void SemanticsUpdateBuilder::updateNode(
   node.platformViewId = platformViewId;
   node.scrollChildren = scrollChildren;
   node.scrollIndex = scrollIndex;
+  node.traversalParent = traversalParent;
   node.scrollPosition = scrollPosition;
   node.scrollExtentMax = scrollExtentMax;
   node.scrollExtentMin = scrollExtentMin;
@@ -113,6 +116,11 @@ void SemanticsUpdateBuilder::updateNode(
     scalarTransform[i] = SafeNarrow(transform.data()[i]);
   }
   node.transform = SkM44::ColMajor(scalarTransform);
+  SkScalar scalarHitTestTransform[16];
+  for (int i = 0; i < 16; ++i) {
+    scalarHitTestTransform[i] = SafeNarrow(hitTestTransform.data()[i]);
+  }
+  node.hitTestTransform = SkM44::ColMajor(scalarHitTestTransform);
   node.childrenInTraversalOrder =
       std::vector<int32_t>(childrenInTraversalOrder.data(),
                            childrenInTraversalOrder.data() +

engine/src/flutter/lib/ui/semantics/semantics_update_builder.h

@@ -40,6 +40,7 @@ class SemanticsUpdateBuilder
       int platformViewId,
       int scrollChildren,
       int scrollIndex,
+      int traversalParent,
       double scrollPosition,
       double scrollExtentMax,
       double scrollExtentMin,
@@ -61,6 +62,7 @@ class SemanticsUpdateBuilder
       std::string tooltip,
       int textDirection,
       const tonic::Float64List& transform,
+      const tonic::Float64List& hitTestTransform,
       const tonic::Int32List& childrenInTraversalOrder,
       const tonic::Int32List& childrenInHitTestOrder,
       const tonic::Int32List& customAccessibilityActions,

engine/src/flutter/lib/web_ui/lib/semantics.dart

@@ -686,6 +686,7 @@ class SemanticsUpdateBuilder {
     required int platformViewId,
     required int scrollChildren,
     required int scrollIndex,
+    required int? traversalParent,
     required double scrollPosition,
     required double scrollExtentMax,
     required double scrollExtentMin,
@@ -704,6 +705,7 @@ class SemanticsUpdateBuilder {
     String? tooltip,
     TextDirection? textDirection,
     required Float64List transform,
+    required Float64List hitTestTransform,
     required Int32List childrenInTraversalOrder,
     required Int32List childrenInHitTestOrder,
     required Int32List additionalActions,
@@ -730,6 +732,7 @@ class SemanticsUpdateBuilder {
         textSelectionExtent: textSelectionExtent,
         scrollChildren: scrollChildren,
         scrollIndex: scrollIndex,
+        traversalParent: traversalParent,
         scrollPosition: scrollPosition,
         scrollExtentMax: scrollExtentMax,
         scrollExtentMin: scrollExtentMin,
@@ -748,6 +751,7 @@ class SemanticsUpdateBuilder {
         tooltip: tooltip,
         textDirection: textDirection,
         transform: engine.toMatrix32(transform),
+        hitTestTransform: engine.toMatrix32(hitTestTransform),
         childrenInTraversalOrder: childrenInTraversalOrder,
         childrenInHitTestOrder: childrenInHitTestOrder,
         additionalActions: additionalActions,