History

Michael Weghorn 4ef0af9c14 wina11y: Deduplicate mapping for IA2TextBoundaryType Add a local function 'lcl_matchIA2TextBoundaryType' that returns the UNO equivalent for the boundary type and use it from all 3 places that previously did the same mapping. Also, use the constants defined in the 'AccessibleTextType.hpp' header rather than hard-coding the values here again. It is unclear to me what the // In New UNO IAccessibleText.idl these constant values are defined as follows: comment refers to, which has been there since commit commit `a18bdb3bc0` Date: Thu Nov 14 08:18:05 2013 +0000 Integrate branch of IAccessible2 Just the winaccessibility directory initially. Change-Id: Ia21abb8d7088646ad6c1f83b3a03e7add716b0c0 (I don't see any IAccessibleText.idl anywhere. Maybe that was meant for some follow-up change that never took place in the end?) Change-Id: I6b8af2215948e8d0241e6f438c0f8cc00adc800f Reviewed-on: https://gerrit.libreoffice.org/c/core/+/119316 Tested-by: Jenkins Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>		2021-07-21 14:35:49 +02:00
..
inc
source
CustomTarget_ia2_idl.mk
Library_uacccom.mk
Library_winaccessibility.mk
Makefile
Module_winaccessibility.mk
README.md
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.