[Webkit-unassigned] [Bug 193348] New: AX: Introduce a static accessibility tree

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Fri Jan 11 00:01:37 PST 2019


            Bug ID: 193348
           Summary: AX: Introduce a static accessibility tree
           Product: WebKit
           Version: Other
          Hardware: All
                OS: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Accessibility
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: cfleizach at apple.com
                CC: webkit-bug-importer at group.apple.com

In order to improve performance when requesting the accessibility hierarchy, we introduce the idea of a "static accessibility tree" which could be accessed on a different thread by assistive technologies.

That is accomplished by storing all the data needed to answer accessibility attribute queries in a static object that mirrors the "live" AccessibilityObjects (which interact with both DOM and Render trees).

These static objects are generally created after layout is done and final tasks are being performed. They are then stored in the static tree representation and able to be read from anywhere.

Tactically this is done with AXStaticTreeNodes inside of an AXStaticTreeCache. The TreeNodes implement an AccessibilityObjectInterface shared with AccessibilityObject

This allows the wrappers to access either one depending on conditions and platforms without significant code duplication or re-organization.

This first patch, outline the architecture. The remaining work is 

1) Store remaining attributes that are accessed within the wrappers
2) Allow accessibility to access this static tree on a different thread
3) Handle parameterized attributes that may require sync back to main thread

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