Re: [orca-list] Off-Screen-Model Suggestions

[Jason White <jason jasonjgw net>]

Keith Hinton <keithint1234 gmail com> wrote:
> I was wondering if there is a chance in the future or if it currently
> exists, that Orca could use an Off Screen Model, or at least provide a
> hotkey on desktop and laptop layouts that will be able to refresh
> Orca's view of what's being displayed on the screen?

If Orca's representation of what is being displayed isn't up to date, then
it's a bug, probably in the application with which Orca is interacting. Please
report it to the Orca Bugzilla.

Regarding the more general question, off-screen models were widely implemented
in the early to mid 1990s by proprietary assistive technologies under several
operating systems. The Mercator project attempted to devise an off-screen
model for the X Window System, but they concluded that this was an infeasible
approach and so developed the concept of an accessibility API, which is what
Orca is based upon.

With an off-screen model, as I understand it, the assistive technology
interrogates the low-level video events in an effort to determine what is
happening in the user interface. The advantage is that no cooperation from
applications and UI libraries is required; the disadvantage is that when the
off-screen model is inaccurate, the user gets incorrect information regarding
the user interface. Off-screen models are also difficult to implement and
complex pieces of software. In fact, I don't know whether it would be possible
to write one in a contemporary X Window System environment. Then there are
performance issues to consider.