836a226205
When handling a SELECTION_CHANGED_REMOVE event, AccDescendantManagerEventListener previously emitted a corresponding EVENT_OBJECT_SELECTIONREMOVE MSAA event with the removed child's ID as a parameter, then deleted that child's accessibility object. This resulted in the accessibility object no longer being available if accessibility tools queried for the object just received in the EVENT_OBJECT_SELECTIONREMOVE event. As a consequence, no 'event_selectionRemove' would be triggered for any table cell object on NVDA side, so an updated selection would not be announced for that case. To keep child objects available for such cases, don't delete the corresponding object in the handler for the SELECTION_CHANGED_REMOVE handler, but remember it for deletion and only do the actual deletion once a subsequent different event is handled. With this in place, the announcement for multiple selected cells in Calc generally works with the NVDA screen reader and a pending NVDA pull request [1] by Leonard de Ruijter in place (s.a. discussion in NVDA issue [2] for more background and further information). (There are still cases where events in response to selection changes are missing, as described e.g. in tdf#118508 and tdf#118748, but those are not winaccessibility-specific and it's the same when using the gtk3 VCL plugin with the Orca screen reader on Linux.) [1] https://github.com/nvaccess/nvda/pull/12849 [2] https://github.com/nvaccess/nvda/issues/9310 Change-Id: I7a46060c501ba9b8288e7c127121a535c60ce2bc Reviewed-on: https://gerrit.libreoffice.org/c/core/+/122169 Tested-by: Jenkins Reviewed-by: Michael Weghorn <m.weghorn@posteo.de> |
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|---|---|---|
| .. | ||
| inc | ||
| source | ||
| CustomTarget_ia2_idl.mk | ||
| Library_uacccom.mk | ||
| Library_winaccessibility.mk | ||
| Makefile | ||
| Module_winaccessibility.mk | ||
| README.md | ||
| WinResTarget_uacccom.mk | ||
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/IAccessible2interfaces to provide native peers for the accessibility code.
- COM implementations of the
-
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.