Fix accessibility location

- Fix GetBounds to return bounds which can be passed to
  AXNodeData.location. Bounds are returned in the following coordinates.
- Bounds of root node are relative to its container, i.e. focused
  window.
- Bounds of non-root node are relative to its tree's root.
- Bounds are returned in non-dip value.

      Android window with ChromeVox. Confirm that focus rectangle is
      shown on right location.

Bug: 764870
Test: enable --enable-chromevox-arc-support and navigate elements on
Change-Id: I052c3da643cd3e017b6256372221a6947410da65
Reviewed-on: https://chromium-review.googlesource.com/671168
Commit-Queue: Yuki Awano <yawano@chromium.org>
Reviewed-by: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#505284}

chrome/browser/chromeos/arc/accessibility/ax_tree_source_arc.cc

@@ -60,22 +60,6 @@ ui::AXEvent ToAXEvent(arc::mojom::AccessibilityEventType arc_event_type) {
   return ui::AX_EVENT_CHILDREN_CHANGED;
 }
 
-const gfx::Rect GetBounds(arc::mojom::AccessibilityNodeInfoData* node) {
-  exo::WMHelper* wm_helper = exo::WMHelper::GetInstance();
-  if (!wm_helper)
-    return gfx::Rect();
-
-  aura::Window* focused_window = wm_helper->GetFocusedWindow();
-  gfx::Rect bounds_in_screen = node->bounds_in_screen;
-  if (focused_window) {
-    aura::Window* toplevel_window = focused_window->GetToplevelWindow();
-    return gfx::ScaleToEnclosingRect(
-        bounds_in_screen,
-        1.0f / toplevel_window->layer()->device_scale_factor());
-  }
-  return bounds_in_screen;
-}
-
 bool GetBooleanProperty(arc::mojom::AccessibilityNodeInfoData* node,
                         arc::mojom::AccessibilityBooleanProperty prop) {
   if (!node->boolean_properties)
@@ -513,10 +497,20 @@ void AXTreeSourceArc::SerializeNode(mojom::AccessibilityNodeInfoData* node,
     out_data->AddBoolAttribute(ui::AX_ATTR_SCROLLABLE, true);
   }
 
-  const gfx::Rect bounds_in_screen = GetBounds(node);
-  out_data->location.SetRect(bounds_in_screen.x(), bounds_in_screen.y(),
-                             bounds_in_screen.width(),
-                             bounds_in_screen.height());
+  exo::WMHelper* wm_helper = exo::WMHelper::GetInstance();
+
+  // To get bounds of a node which can be passed to AXNodeData.location,
+  // - Root node must exist.
+  // - Window where this tree is attached to need to be focused.
+  if (root_id_ != -1 && wm_helper) {
+    aura::Window* focused_window = wm_helper->GetFocusedWindow();
+    if (focused_window) {
+      const gfx::Rect bounds_in_screen = GetBounds(node, focused_window);
+      out_data->location.SetRect(bounds_in_screen.x(), bounds_in_screen.y(),
+                                 bounds_in_screen.width(),
+                                 bounds_in_screen.height());
+    }
+  }
 
   if (out_data->role == ui::AX_ROLE_TEXT_FIELD && !text.empty())
     out_data->AddStringAttribute(ui::AX_ATTR_VALUE, text);
@@ -550,6 +544,35 @@ void AXTreeSourceArc::SerializeNode(mojom::AccessibilityNodeInfoData* node,
   }
 }
 
+const gfx::Rect AXTreeSourceArc::GetBounds(
+    mojom::AccessibilityNodeInfoData* node,
+    aura::Window* focused_window) const {
+  DCHECK(focused_window);
+  DCHECK(root_id_ != -1);
+
+  gfx::Rect node_bounds = node->bounds_in_screen;
+
+  if (node->id == root_id_) {
+    // Top level window returns its bounds in dip.
+    aura::Window* toplevel_window = focused_window->GetToplevelWindow();
+    float scale = toplevel_window->layer()->device_scale_factor();
+
+    // Bounds of root node is relative to its container, i.e. focused window.
+    node_bounds.Offset(
+        static_cast<int>(-1.0f * scale *
+                         static_cast<float>(toplevel_window->bounds().x())),
+        static_cast<int>(-1.0f * scale *
+                         static_cast<float>(toplevel_window->bounds().y())));
+
+    return node_bounds;
+  }
+
+  // Bounds of non-root node is relative to its tree's root.
+  gfx::Rect root_bounds = GetFromId(root_id_)->bounds_in_screen;
+  node_bounds.Offset(-1 * root_bounds.x(), -1 * root_bounds.y());
+  return node_bounds;
+}
+
 void AXTreeSourceArc::PerformAction(const ui::AXActionData& data) {
   delegate_->OnAction(data);
 }

chrome/browser/chromeos/arc/accessibility/ax_tree_source_arc.h

@@ -75,6 +75,14 @@ class AXTreeSourceArc
   void SerializeNode(mojom::AccessibilityNodeInfoData* node,
                      ui::AXNodeData* out_data) const override;
 
+  // Returns bounds of a node which can be passed to AXNodeData.location. Bounds
+  // are returned in the following coordinates depending on whether it's root or
+  // not.
+  // - Root node is relative to its container, i.e. focused window.
+  // - Non-root node is relative to the root node of this tree.
+  const gfx::Rect GetBounds(mojom::AccessibilityNodeInfoData* node,
+                            aura::Window* focused_window) const;
+
   // AXHostDelegate overrides.
   void PerformAction(const ui::AXActionData& data) override;