Re: GNOME Shell Magnifier Advanced Settings and Testing

Hello, Joseph.

As concerning the Mouse Position Polling under Unity, this was done through the Compiz eZoom settings. I don't think I did a good job at clarifying. When I made the changes to the GNOME Shell magnifier code, I did this while I was in Unity. I then logged out of Unity and went back into GNOME to test what I changed. I apologize for not clarifying that.

As far as the dialog goes, I was indeed referring to the magnifier Preferences Dialog, and I would love to have a copy for testing, but if it would be too much trouble then please don't worry about it; I do not want you to have to take time away from more important things. If all else, I can just learn to use GSettings and proceed from there.

I am really excited about where everything is going in the way of Linux Accessibility!

Thanks for taking the time to read through my messages and for giving your input and advice.

Take care.

On 01/27/2012 07:54 AM, Joseph Scheuhammer wrote:
Hi Robert,

Thanks very much for your input!
I saw some screenshots of a more advanced dialog for magnifier settings on the GNOME Shell magnification page [1].

I assume you are talking about the " Magnifier Preferences Dialog" section [1]. You might also want to track the work on the proposed 3.4 features [2]. There is a page about the preferences dialog [3], inversion/brightness/contrast effects [4], and focus tracking [5].

I also read some references to a testing dialog here [2], but it seems that this has been discontinued (?).

Yes, it has been discontinued even though I still use if for testing (I wrote it). I'm not sure exactly when the control panel is going to be released, but if you can't wait, and you really want a copy of the test dialog, I could probably put something together for you. Or, get the control panel to you before it's released. Note, I said "probably", meaning I'd want to proceed with caution as I don't want to muck up your system accidentally.

I have been reading through this file:


and, unfortunately, I really would not know where to begin as far as the settings are concerned ...

Yes, that's the source code, but it's not really the thing to read to find out the settings. That's like looking for a needle in a haystack :-). The preferences (the GSettings) are listed at the beginning [6] of the GNOME Shell Magnifier page that you cited, although it is a technical description. But, for now, take a look at the "User Features" section [6] and see if you can make sense of it. I'll happily answer any questions you might have.


So I contemplated whether I should change this value from 50 to 1. I gave in and did it!

I made the changes from within Unity2D, so I logged out and then logged into GNOME Shell. I crossed my fingers and then hit CTRL+ALT+M, the keyboard shortcut I set to activate the magnifier...and...VOILA! Super smooth panning!

I'm not sure if you changed the magnifier code or something else in Unity2D (or both). I'll try changing just the magnifier.js code to use a poll frequency of "1" as you did to see what happens. FYI, I'm developing on Fedora-16 -- no Unity there.

Secondly, in a perfect world there shouldn't be any polling at all. The magnifier is polling the mouse to detect when it moves and to determine where it is on the screen. There should be a way for the magnifier to ask to be notified when the mouse moves (a callback scenario). Alas, that capacity does not exist within X11, which is locus of that information.

Thirdly, you wrote:
How likely is it that decreasing this value from 50 to 1 will cause possible instabilities? Is it set to 50 for any given reason (I am sure there has to be a reason)? I ask this because it is the same way with Compiz, but it seems (in either case) that the lower the Poll Interval (Compiz) or Poll Frequency (GNOME shell Magnifier) the more smoothly panning is in fullscreen magnification mode.

Poll too often, and the system slows down since it's spending a too much time asking "where's the mouse?". That probably explains the panning lag you are seeing. Poll too infrequently and the position information is out of sync with the actual mouse. A consequence is that the the magnified mouse cursor image is positioned incorrectly (it lags behind the actual mouse), and that could lead to clicking on something that you didn't mean to click on. The polling frequency was set to 50 since that was a reasonable compromise.

But, it almost sounds like the frequency should be a user preference. I say "almost" since there should be a value that represents an adequate compromise. And, I'm not sure what other factors are at play -- for example, with a faster graphics system, perhaps polling more frequently would not lead to any detriment. Hmmm....

Is there a need for testers as concerning the magnifier?

Absolutely! Especially user testing. The magnifier was developed based on a number of inputs. The older gnome CORBA service -- "gnome-mag" -- needed to be replaced. The GNOME Shell magnifier represents a partial duplication of gnome-mag's functionality. Also, others were asked for their input along the way. For example, one of my co-workers is an occupational therapist who works with low vision clients, and I've asked her for guidance on numerous occasions. Having actual users out there saying what they need or want is another important source.

Thanks for taking the time to read through my tons of e-mails, ...

All I can say to that is:  "keep them coming".

Thanks, and I hope this helps.


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