AX: should be able to compute AXPosition using the isolated tree

https://bugs.webkit.org/show_bug.cgi?id=267957
rdar://problem/121472048

Reviewed by Andres Gonzalez.

The relative frame that we're caching in the isolated tree is already
in the correct screen coordinates, all that's necessary is to cache
the screen relative position of the root, and then add them together.

We can update the cached root position when AXGeometryManager
updates object regions.

There isn't an easy way to write a layout test for this, as there
doesn't seem to be a way to move the window's origin.

In order to manually test this, I temporarily disabled AXRelativeFrame,
forcing VoiceOver to use AXPosition for every element, then I checked
that the bounds are correct when navigating and when moving and resizing
the window.

The main performance win I observe is when VoiceOver tries to focus on the
root web area when the page is busy. Without this patch, VoiceOver can
get blocked on the main thread, but with this patch it's no longer blocked.

* Source/WebCore/accessibility/AXGeometryManager.cpp:
(WebCore::AXGeometryManager::willUpdateObjectRegions):
* Source/WebCore/accessibility/isolatedtree/AXIsolatedObject.cpp:
(WebCore::AXIsolatedObject::screenRelativePosition const):
* Source/WebCore/accessibility/isolatedtree/AXIsolatedTree.cpp:
(WebCore::AXIsolatedTree::updateNodeProperties):
(WebCore::AXIsolatedTree::updateRootScreenRelativePosition):
* Source/WebCore/accessibility/isolatedtree/AXIsolatedTree.h:

Canonical link: https://commits.webkit.org/273716@main

Source/WebCore/accessibility/AXGeometryManager.cpp

@@ -112,6 +112,12 @@ void AXGeometryManager::willUpdateObjectRegions()
 {
     if (m_updateObjectRegionsTimer.isActive())
         m_updateObjectRegionsTimer.stop();
+
+    if (!m_cache)
+        return;
+
+    if (RefPtr tree = AXIsolatedTree::treeForPageID(m_cache->pageID()))
+        tree->updateRootScreenRelativePosition();
 }
 
 void AXGeometryManager::scheduleRenderingUpdate()

Source/WebCore/accessibility/isolatedtree/AXIsolatedObject.cpp

@@ -1206,6 +1206,15 @@ FloatPoint AXIsolatedObject::screenRelativePosition() const
     if (auto point = optionalAttributeValue<FloatPoint>(AXPropertyName::ScreenRelativePosition))
         return *point;
 
+    if (auto rootNode = tree()->rootNode()) {
+        if (auto rootPoint = rootNode->optionalAttributeValue<FloatPoint>(AXPropertyName::ScreenRelativePosition)) {
+            // Relative frames are top-left origin, but screen relative positions are bottom-left origin.
+            FloatRect rootRelativeFrame = rootNode->relativeFrame();
+            FloatRect relativeFrame = this->relativeFrame();
+            return { rootPoint->x() + relativeFrame.x(), rootPoint->y() + (rootRelativeFrame.maxY() - relativeFrame.maxY()) };
+        }
+    }
+
     return Accessibility::retrieveValueFromMainThread<FloatPoint>([&, this] () -> FloatPoint {
         if (auto* axObject = associatedAXObject())
             return axObject->screenRelativePosition();

Source/WebCore/accessibility/isolatedtree/AXIsolatedTree.cpp

@@ -645,6 +645,9 @@ void AXIsolatedTree::updateNodeProperties(AXCoreObject& axObject, const AXProper
         case AXPropertyName::CellScope:
             propertyMap.set(AXPropertyName::CellScope, axObject.cellScope().isolatedCopy());
             break;
+        case AXPropertyName::ScreenRelativePosition:
+            propertyMap.set(AXPropertyName::ScreenRelativePosition, axObject.screenRelativePosition());
+            break;
         case AXPropertyName::SelectedTextRange:
             propertyMap.set(AXPropertyName::SelectedTextRange, axObject.selectedTextRange());
             break;
@@ -1017,6 +1020,18 @@ void AXIsolatedTree::updateFrame(AXID axID, IntRect&& newFrame)
     m_pendingPropertyChanges.append({ axID, WTFMove(propertyMap) });
 }
 
+void AXIsolatedTree::updateRootScreenRelativePosition()
+{
+    AXTRACE("AXIsolatedTree::updateRootScreenRelativePosition"_s);
+    ASSERT(isMainThread());
+
+    if (!rootNode())
+        return;
+
+    if (auto* axRoot = rootNode()->associatedAXObject())
+        updateNodeProperties(*axRoot, { AXPropertyName::ScreenRelativePosition });
+}
+
 void AXIsolatedTree::removeNode(const AccessibilityObject& axObject)
 {
     AXTRACE("AXIsolatedTree::removeNode"_s);

Source/WebCore/accessibility/isolatedtree/AXIsolatedTree.h

@@ -348,6 +348,7 @@ class AXIsolatedTree : public ThreadSafeRefCountedAndCanMakeThreadSafeWeakPtr<AX
     void updateDependentProperties(AccessibilityObject&);
     void updatePropertiesForSelfAndDescendants(AccessibilityObject&, const AXPropertyNameSet&);
     void updateFrame(AXID, IntRect&&);
+    void updateRootScreenRelativePosition();
     void overrideNodeProperties(AXID, AXPropertyMap&&);
 
     double loadingProgress() { return m_loadingProgress; }