on 2006-05-07 8:48 PM, Laurence Harris at email@hidden wrote:
> Any performance issues, or would that only arise if something is actually
> accessing your applications?
There shouldn't be a performance impact on a "controlled" application, since
the accessibility routines built into all standard Carbon and Cocoa UI
elements are passive when they aren't being called, even if access for
assistive devices is turned on. Even when an assistive application is
"reading the screen" on an application's window or telling the target
application to check a checkbox or whatever, the accessibility code is at a
very low level and is very fast -- orders of magnitude faster than doing the
same thing via an AppleScript command.
There is reportedly a very slight performance impact on an "observed"
application -- that is, an application that an assistive application is
currently registered with in order to receive notifications when the target
application's UI elements are used. In Tiger and, I believe, in Panther, the
code was tweaked so that there is no performance penalty at all in an
application for which no assistive application is currently registered as an
observer, even if access for assistive devices is turned on. Even when an
assistive application is registered, the notification code was reportedly
optimized and is now much faster than it was in Jaguar.
When I use accessibility, I see no discernable impact. I believe you would
have to use profiling tools to see it. You can get a feel for it in the real
world by playing with Apple's Accessibility Inspector -- it's a screen
reader that is installed with Developer Tools. Launch it, then move the
mouse around over Photoshop windows while you're doing some intensive image
manipulation, and see if you notice an issue -- I don't think you will.
To see notifications in action, download the 30-day trial version of PreFab
UI Browser at www.prefab.com/uibrowser/. You can use its Notification drawer
to register to observe notifications from any target application, and open
the Notifications Log window to watch the notifications come in as you play
with the target application.
--
Bill Cheeseman - email@hidden
Quechee Software, Quechee, Vermont, USA
http://www.quecheesoftware.com
PreFab Software - http://www.prefab.com/scripting.html
The AppleScript Sourcebook - http://www.AppleScriptSourcebook.com
Vermont Recipes - http://www.stepwise.com/Articles/VermontRecipes
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