Bug#874054: Setting QT_LINUX_ACCESSIBILITY_ALWAYS_ON=1 has a huge negative performance impact, should not be always on

[Samuel Thibault]

Control: reassign -1 libqt5core5a
Control: retitle -1 Setting QT_LINUX_ACCESSIBILITY_ALWAYS_ON=1 has a huge negative performance impact, qt accessibility should not always send all messages

Hello,

Lisandro Damián Nicanor Pérez Meyer, on sam. 02 sept. 2017 11:02:15 -0300, wrote:
> According to [upstream] setting QT_LINUX_ACCESSIBILITY_ALWAYS_ON=1 has a
> huge negative performace impact on Qt,

Upstream said "big", not "huge" :)

> so it should not be enabled by default.

On the long run, it really should.  Just hiding issues is not the way
forward :)

Also, note that if the performance is so bad, it means something *needs*
to be fixed, otherwise blind users will get the bad performance, and
nobody will be there to fix it, because nobody notices it except blind
users, who are left with little hope to fix it by themselves.

> Upstream suggested that maybe we should try to only set this variable if
> the appropriate hardware is found.

Sebastian Humenda, on sam. 02 sept. 2017 16:18:16 +0200, answered:
> This is not a good idea, because not all screen reader users have dedicated
> hardware. Users only using speech for navigation would be without Qt a11y.

Exactly.

> Couldn't we detect whether a screen reader (Orca) is installed, or is this a
> default on Desktop systems, these days?

It is a default, and that is on purpose.

Lisandro Damián Nicanor Pérez Meyer, on sam. 02 sept. 2017 11:28:51 -0300, wrote:
> On the other hand people needing a11y really need to get this on as
> simple as possible.

And that's precisely the issue.

If at-spi is not installed and enabled by default, it's a real pain to
make a system accessible with a screen reader: you first have to divine
which package should be installed, then enable accessibility in some
control panel, and log out / re login, so that at-spi gets started. That
just can not work.  While having it enabled by default, ready to be
activated, it's just a matter of pressing e.g. ctrl-alt-s to start
speech.  That's a *huge* difference for blind people.  This is discussed
in more details in my talk at DC15.

https://summit.debconf.org/debconf15/meeting/290/thanks-for-maintaining-a-desktop-environment-but-is-it-accessible/

Lisandro Damián Nicanor Pérez Meyer, on sam. 02 sept. 2017 14:34:01 -0300, wrote:
> Basically: Qt issuing all the necessary messages for a11y in machines
> not needing a11y makes a lot of cpu power waste, whether you notice it
> or not.

Ok, so it seems Qt does not implement the optimization that Gtk did.
Normally Qt should only send events that were requested by a screen
reader.

See the notification part of

https://www.freedesktop.org/wiki/Accessibility/Walkthrough/

It'd be useful if you could contribute text for the Qt part, btw :)

Samuel