History

Michael Weghorn d4f6534e88 [API CHANGE] a11y: Use XAccessible for relation targets Use a Sequence of XAccessible rather than its base interface XInterface for AccessibleRelation's TargetSet. As the targets are accessible objects as well, anything other than XAccessible doesn't make much sense. Using XAccessible right away makes that clearer and avoids the need to query the XAccessible interface. (The winaccessibility bridge was already using `static_cast`, relying on the fact that the objects are XAccessibles.) The a11y UNO API is not published, so an API change should be unproblematic. Change-Id: I7f08e98d1ec303d5343d9a7954187cdd71495ebc Reviewed-on: https://gerrit.libreoffice.org/c/core/+/166586 Reviewed-by: Michael Weghorn <m.weghorn@posteo.de> Tested-by: Jenkins		2024-04-24 23:04:35 +02:00
..
inc	wina11y: Drop unnecessary null check and make static	2024-04-17 21:33:06 +02:00
source	[API CHANGE] a11y: Use XAccessible for relation targets	2024-04-24 23:04:35 +02:00
CustomTarget_ia2_idl.mk	tdf#135586 a11y: Make IAccessible2 an external and update it	2023-10-25 20:48:07 +02:00
Library_uacccom.mk	wina11y: Report actual app/toolkit name/version	2022-09-10 07:21:17 +02:00
Library_winaccessibility.mk	wina11y: Drop AccObjectManagerAgent indirection	2023-08-08 08:18:28 +02:00
Makefile
Module_winaccessibility.mk	Clean up dead uses of DISABLE_ATL	2019-01-24 21:23:56 +01:00
README.md	Updated README.md files to represent current code / use Markdown format	2021-04-07 17:47:16 +02:00
WinResTarget_uacccom.mk

README.md

Windows Accessibility Bridge

This code provides a bridge between our internal Accessibility interfaces (implemented on all visible 'things' in the suite: eg. windows, buttons, entry boxes etc.) - and the Windows MSAA / IAccessible2 COM interfaces that are familiar to windows users and Accessible Technologies (ATs) such as the NVDA screen reader.

The code breaks into three bits:

source/service/
- the UNO service providing the accessibility bridge. It essentially listens to events from the LibreOffice core and creates and synchronises COM peers for our internal accessibility objects when events arrive.
source/UAccCom/
- COM implementations of the MSAA / IAccessible2 interfaces to provide native peers for the accessibility code.
source/UAccCOMIDL/
- COM Interface Definition Language (IDL) for UAccCom.

Here is one way of visualising the code / control flow

VCL <-> UNO toolkit <-> UNO a11y <-> win a11y <-> COM / IAccessible2

vcl/ <-> toolkit/ <-> accessibility/ <-> winaccessibility/ <-> UAccCom/

Threading

It's possible that the UNO components are called from threads other than the main thread, so they have to be synchronized. It would be nice to put the component into a UNO apartment (and the COM components into STA) but UNO would spawn a new thread for it so it's not possible. The COM components also call into the same global AccObjectWinManager as the UNO components do so both have to be synchronized in the same way.

So we use the SolarMutex for all synchronization since anything else would be rather difficult to make work. Unfortunately there is a pre-existing problem in vcl with Win32 Window creation and destruction on non-main threads where a synchronous SendMessage is used while the SolarMutex is locked that can cause deadlocks if the main thread is waiting on the SolarMutex itself at that time and thus not handing the Win32 message; this is easy to trigger with JunitTests but hopefully not by actual end users.

Debugging / Playing with winaccessibility

If NVDA is running when soffice starts, IA2 should be automatically enabled and work as expected. In order to use 'accprobe' to debug it is necessary to override the check for whether an AT (like NVDA) is running; to do that use:

SAL_FORCE_IACCESSIBLE2=1 soffice.exe -writer

Then you can use accprobe to introspect the accessibility hierarchy remotely, checkout:

http://accessibility.linuxfoundation.org/a11yweb/util/accprobe/

But often it's more useful to look at NVDA's text output window.