Implement i18n features in the a11y API. (#4029)

lib/ui/semantics.dart

@@ -203,7 +203,8 @@ class SemanticsUpdateBuilder extends NativeFieldWrapperClass2 {
   /// asynchronously, the [Window.onSemanticsAction] callback might be called
   /// with an action that is no longer possible.
   ///
-  /// The `label` is a string that describes this node.
+  /// The `label` is a string that describes this node. Its reading direction is
+  /// given by `textDirection`.
   ///
   /// The `rect` is the region occupied by this node in its own coordinate
   /// system.
@@ -216,6 +217,7 @@ class SemanticsUpdateBuilder extends NativeFieldWrapperClass2 {
     int actions,
     Rect rect,
     String label,
+    TextDirection textDirection,
     Float64List transform,
     Int32List children
   }) {
@@ -229,6 +231,7 @@ class SemanticsUpdateBuilder extends NativeFieldWrapperClass2 {
                 rect.right,
                 rect.bottom,
                 label,
+                textDirection != null ? textDirection.index + 1 : 0,
                 transform,
                 children);
   }
@@ -241,6 +244,7 @@ class SemanticsUpdateBuilder extends NativeFieldWrapperClass2 {
     double right,
     double bottom,
     String label,
+    int textDirection,
     Float64List transform,
     Int32List children
   ) native "SemanticsUpdateBuilder_updateNode";

lib/ui/semantics/semantics_node.h

@@ -45,6 +45,8 @@ struct SemanticsNode {
   int32_t flags = 0;
   int32_t actions = 0;
   std::string label;
+  int32_t textDirection = 0; // 0=unknown, 1=rtl, 2=ltr
+
   SkRect rect = SkRect::MakeEmpty();
   SkMatrix44 transform = SkMatrix44(SkMatrix44::kIdentity_Constructor);
   std::vector<int32_t> children;

lib/ui/semantics/semantics_update_builder.cc

@@ -42,6 +42,7 @@ void SemanticsUpdateBuilder::updateNode(int id,
                                         double right,
                                         double bottom,
                                         std::string label,
+                                        int textDirection,
                                         const tonic::Float64List& transform,
                                         const tonic::Int32List& children) {
   SemanticsNode node;
@@ -50,6 +51,7 @@ void SemanticsUpdateBuilder::updateNode(int id,
   node.actions = actions;
   node.rect = SkRect::MakeLTRB(left, top, right, bottom);
   node.label = label;
+  node.textDirection = textDirection;
   node.transform.setColMajord(transform.data());
   node.children = std::vector<int32_t>(
       children.data(), children.data() + children.num_elements());

lib/ui/semantics/semantics_update_builder.h

@@ -33,6 +33,7 @@ class SemanticsUpdateBuilder
                   double right,
                   double bottom,
                   std::string label,
+                  int textDirection,
                   const tonic::Float64List& transform,
                   const tonic::Int32List& children);
 

shell/platform/android/io/flutter/view/AccessibilityBridge.java

@@ -190,7 +190,7 @@ class AccessibilityBridge extends AccessibilityNodeProvider {
                 if ((object.actions & SEMANTICS_ACTION_SCROLL_UP) != 0) {
                     mOwner.dispatchSemanticsAction(virtualViewId, SEMANTICS_ACTION_SCROLL_UP);
                 } else if ((object.actions & SEMANTICS_ACTION_SCROLL_LEFT) != 0) {
-                    // TODO(ianh): bidi support
+                    // TODO(ianh): bidi support using textDirection
                     mOwner.dispatchSemanticsAction(virtualViewId, SEMANTICS_ACTION_SCROLL_LEFT);
                 } else if ((object.actions & SEMANTICS_ACTION_INCREASE) != 0) {
                     mOwner.dispatchSemanticsAction(virtualViewId, SEMANTICS_ACTION_INCREASE);
@@ -203,7 +203,7 @@ class AccessibilityBridge extends AccessibilityNodeProvider {
                 if ((object.actions & SEMANTICS_ACTION_SCROLL_DOWN) != 0) {
                     mOwner.dispatchSemanticsAction(virtualViewId, SEMANTICS_ACTION_SCROLL_DOWN);
                 } else if ((object.actions & SEMANTICS_ACTION_SCROLL_RIGHT) != 0) {
-                    // TODO(ianh): bidi support
+                    // TODO(ianh): bidi support using textDirection
                     mOwner.dispatchSemanticsAction(virtualViewId, SEMANTICS_ACTION_SCROLL_RIGHT);
                 } else if ((object.actions & SEMANTICS_ACTION_DECREASE) != 0) {
                     mOwner.dispatchSemanticsAction(virtualViewId, SEMANTICS_ACTION_DECREASE);
@@ -347,6 +347,20 @@ class AccessibilityBridge extends AccessibilityNodeProvider {
         sendAccessibilityEvent(0, AccessibilityEvent.TYPE_WINDOW_CONTENT_CHANGED);
     }
 
+    private enum TextDirection {
+        UNKNOWN, LTR, RTL;
+
+        public static TextDirection fromInt(int value) {
+            switch (value) {
+                case 1:
+                    return RTL;
+                case 2:
+                    return LTR;
+            }
+            return UNKNOWN;
+        }
+    }
+
     private class SemanticsObject {
         SemanticsObject() { }
 
@@ -355,6 +369,7 @@ class AccessibilityBridge extends AccessibilityNodeProvider {
         int flags;
         int actions;
         String label;
+        TextDirection textDirection;
 
         private float left;
         private float top;
@@ -394,6 +409,8 @@ class AccessibilityBridge extends AccessibilityNodeProvider {
             else
                 label = strings[stringIndex];
 
+            textDirection = TextDirection.fromInt(buffer.getInt());
+
             left = buffer.getFloat();
             top = buffer.getFloat();
             right = buffer.getFloat();

shell/platform/android/platform_view_android.cc

@@ -421,7 +421,7 @@ bool PlatformViewAndroid::ResourceContextMakeCurrent() {
 
 void PlatformViewAndroid::UpdateSemantics(
     std::vector<blink::SemanticsNode> update) {
-  constexpr size_t kBytesPerNode = 25 * sizeof(int32_t);
+  constexpr size_t kBytesPerNode = 26 * sizeof(int32_t);
   constexpr size_t kBytesPerChild = sizeof(int32_t);
 
   JNIEnv* env = fml::jni::AttachCurrentThread();
@@ -443,6 +443,8 @@ void PlatformViewAndroid::UpdateSemantics(
     std::vector<std::string> strings;
     size_t position = 0;
     for (const blink::SemanticsNode& node : update) {
+      // If you edit this code, make sure you update kBytesPerNode
+      // above to match the number of values you are sending.
       buffer_int32[position++] = node.id;
       buffer_int32[position++] = node.flags;
       buffer_int32[position++] = node.actions;
@@ -452,6 +454,7 @@ void PlatformViewAndroid::UpdateSemantics(
         buffer_int32[position++] = strings.size();
         strings.push_back(node.label);
       }
+      buffer_int32[position++] = node.textDirection;
       buffer_float32[position++] = node.rect.left();
       buffer_float32[position++] = node.rect.top();
       buffer_float32[position++] = node.rect.right();

shell/platform/darwin/ios/framework/Source/accessibility_bridge.mm

@@ -23,10 +23,10 @@ blink::SemanticsAction GetSemanticsActionForScrollDirection(
   // directions, which is why the following maps left to right and vice versa.
   switch (direction) {
     case UIAccessibilityScrollDirectionRight:
-    case UIAccessibilityScrollDirectionPrevious:  // TODO(abarth): Support RTL.
+    case UIAccessibilityScrollDirectionPrevious:  // TODO(abarth): Support RTL using _node.textDirection.
       return blink::SemanticsAction::kScrollLeft;
     case UIAccessibilityScrollDirectionLeft:
-    case UIAccessibilityScrollDirectionNext:  // TODO(abarth): Support RTL.
+    case UIAccessibilityScrollDirectionNext:  // TODO(abarth): Support RTL using _node.textDirection.
       return blink::SemanticsAction::kScrollRight;
     case UIAccessibilityScrollDirectionUp:
       return blink::SemanticsAction::kScrollDown;