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Michael Weghorn 02edbf7dc7 tdf#154303 wina11y: Don't truncate 64-bit states 
commit 8d8e6c84e5
    Date:   Sun Jul 3 20:29:28 2022 +0200

        [API CHANGE] Drop css::accessibility::XAccessibleStateSet

had introduced the use of a 64-bit integer with
bit flags for the accessible states.

However, `AccObjectWinManager::DecreaseState` and
`AccObjectWinManager::IncreaseState` were still using
unsigned short, resulting in truncation.

As one result, the `AccessibleEventId::STATE_CHANGED`
event with state `AccessibleStateType::VISIBLE`
from `OAccessibleMenuBaseComponent::SetVisible` would no
longer result in the `STATE_SYSTEM_INVISIBLE` being unset
and thus the the JAWS screen reader would no longer announce
the focused (but considered invisible) menu item.

Fix this by switching the param for those two methods to
sal_Int64 as well.

Change-Id: I714573e2691e82c6287a4b83f872f87568e46495
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/149255
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>
2023-03-22 06:36:58 +00:00
..
inc tdf#154303 wina11y: Don't truncate 64-bit states 2023-03-22 06:36:58 +00:00
source tdf#154303 wina11y: Don't truncate 64-bit states 2023-03-22 06:36:58 +00:00
CustomTarget_ia2_idl.mk wina11y: Drop unused AccessibleKey{Binding,Stroke}.idl 2022-08-05 17:35:16 +02:00
Library_uacccom.mk wina11y: Report actual app/toolkit name/version 2022-09-10 07:21:17 +02:00
Library_winaccessibility.mk Generally determine Rdb content from gb_*_set_componentfile calls 2021-12-10 08:14:24 +01:00
Makefile Add custom target to process IA2 COM idl files 2013-11-19 10:02:23 +00:00
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 prefer makefile-gmake-mode 2014-04-28 23:35:42 +09:00

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.