Smoother Panning in GNOME Shell Magnifier

Alan Bell alanbell at
Thu Jan 26 09:11:41 UTC 2012

I guess there must be a performance penalty from polling the mouse so 
often (can't imagine why that setting exists if there isn't one) and 
that value is in milliseconds, so 1/1000 of a second. Assuming a screen 
refresh rate of 60Hz each screen refresh takes 16ms so I think if the 
setting is put at 15ms then a mouse poll will happen during every screen 
refresh cycle. From my testing I can't tell the difference between a 
setting of 15 and a setting of 1. Whatever the performance hit is (I 
couldn't detect one but a low performance netbook might struggle) I 
would imagine that a setting of 15 would be easier to argue to move to 
than 1 because its only a change of about a factor of 3 rather than a 
factor of 50.
Is 15 as good as 1 for you?


On 26/01/12 02:01, Robert cole wrote:
> Hello, everyone.
> Well, I did a slight bit of tinkering with the GNOME Shell Magnifier 
> settings today (I love that I can tinker in Linux!).
> I am not trying to complain by any means, so I hope that this does not 
> sound as such. I have been trying out Unity2D in Ubuntu 11.10, which I 
> recently installed onto my desktop system to replace Linux Mint 12. I 
> love how the GNOME Shell Magnifier is coming along, but at the present 
> time it does not pan as smoothly as I am used to, which makes it 
> slightly more difficult to read and to navigate my system. The same 
> can be said for panning using Compiz's eZoom plugin on a fresh install 
> of Ubuntu--it does not pan so smoothly either.
> Well...I learned through experience that I could change the value for 
> Compiz's Mouse position polling plugin to smoothen things out. (Just 
> for the record, the GNOME Shell Magnifier pans much more smoothly by 
> default as compared to Compiz's default settings under Unity.) Anyway, 
> I learned that if I decrease the Mouse Poll Interval from 40 to 1 
> panning was very smooth...well...just beautiful to me.
> So today, rather than bother the list by asking where I could find the 
> settings files for the Zoom feature, I figured I'd do some 
> exploration. I ran the basic command:
> locate magnifier
> and this file stood out to me:
> /usr/share/gnome-shell/js/ui/magnifier.js
> I am not a professional programmer, but I figured I'd take a look at 
> this file. I fired up nano (after making a backup of the file to my 
> /home directory) and began reading. I found the following line under 
> the first set of functions at the top of the file (section comment 
> below):
> // Keep enums in sync with GSettings schemas
> [...]
> 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! This made me love GNOME Shell even more than I 
> already do!
> My questions as concerning this thread, though, is this: 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.
> In any case, I just wanted to put this on the list to get some input. 
> As I mentioned earlier, I am definitely not a professional programmer. 
> I took classes in C++, Visual Basic, and Python throughout the years, 
> but I the class content was quite basic.
> thanks for any input regarding this subject. I'm really looking 
> forward to GNOME 3.4!
> Take care.
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