a strange condition on X - is there a full display magnifier?

[Skaperen]

this happened just once, and i don't what feature this might be and how it got enabled. i later rebooted again and this strange condition did not come back. just before dinner i rebooted to do an upgrade, but i didn't have enough time. i logged in 4 users, one of which is the digital clock display user. dinner was earlier than usual, tonight. as usual, i left the computer running on the clock display. after dinner, i noticed the right side of the clock was cut off at the edge and there was no xfce panel being display. when i got back to the computer and turned the mouse back on, i was planning to first see what was up with the panel being gone or covered by the clock window. instead, as i moved the mouse around the contents on the screen also moved slowly in the opposite direction. it was still working with a 1920x1080 buffer as far as a few programs could see. the monitor was getting a subset of the 1920x1080. it looked at least 90%. fonts did look larger. i could find out the buffer size (1920x1080) but i could not find a tool that would reveal what X thought the display size is (the video it was sending out to the monitor). i switched user among the 4 users i had logged in. this only affected 2 of the users. the other 2 were normal. their screens did not move around.

is this some kind of magnify feature that i don't know about? it could be nice to use if i had control over it, especially if i can go back to normal when done. i'm wondering how i might have engaged that. i find nothing suggestive in the keyboard shortcuts or list of installed packages. if this was a magnifier is was doing only about a 10% increase. the difference, unlike xmag, is that it was magnifying the whole screen. googling for this finds such a feature for all popular systems, with it being built-in on Mac OS X. what is not clear is whether these are window (like xmag) magnifiers or full screen magnifiers (like what i effectively had). i tried scanning /usr but grepping for "magn" has no useful results and "mag" has too many to read (5943) because of so many names with word like "image".

i am particularly curious how i could have accidentally enabled in for 2 users.

[Skaperen]

i found the feature in xfce ... alt+mouse scroll zooms the whole screen in and out ... nice

[Holger_Gehrke]

Yeah, it's a new(-ish) feature in XFCE 4.11 (or so), so it's been there for the last three or four years. Found out about it a few days after getting my first pair of reading glasses a few months ago.

If you want the old behaviour (alt+scrollwheel on titlebar of a window changes it's transparency) back, you can set the property 'zoom_desktop' in the channel xfwm4 of xfconf to false either using xfce4-settings-editor or with

xfconf-query -c xfwm4 -p /general/zoom_desktop --set false

Might even be possible to write a script to toggle between the two states and assign it to a key ...

Holger

[Skaperen]

i don't think i need the old feature. i may, some day, look for the zoom source code to see if i can change it to not move the view when the mouse moves within the area being viewed.

[Skaperen]

if i can change the way mouse movement works ... not move viewed portion until the point hits the edge, than drag the view as the mouse tries to move the pointer past the edge ... then it could be useful, in some cases, to run X with a buffer even larger than the video display, with the viewed area the same size as the video display.

[Holger_Gehrke]

That's already possible with xrandr with the --fb and --panning options. Example

xrandr --output HDMI-0 --fb 3840x2160 --panning 3840x2160

gives me a moving "window" of 1920x1080 (display resolution) into a desktop of 3840x2160. There's several more optional parameters to '--panning' to control the panning behaviour.

Holger

[Skaperen]

does xrandr do this to only one instance of X? i usually run several userids, each on their own X server, switched around with os.execvp('dm-tool',['dm-tool','switch-to-user',sys.argv[1]]) (Python), via lightdm.

[Skaperen]

is that command correct? i see "3840x2160" in it twice and "1920x1080" not at all.

[Holger_Gehrke]

re. #7:
AFAIK it should only affect the display it's connecting to, either set through the option '-d' or '--display' or taken from '$DISPLAY'.

re. #8:
I probably phrased that badly. '--fb' defines the size of the framebuffer, '--panning' defines the area to move around in and they can be different. The sizes of the moving "window" is the resolution the display is set to, which on my machines is currently 1920x1080. If I changed resolution it wouldn't affect either the buffer or the panning area, so I could just as easily have a movable 1024x768 'window' in that buffer by using '--mode 1024x768'.

Holger

PS: while playing around with this I got into several situation where I couldn't come up with the right parameters to undo my changes. No need to panic if that happens, 'xfce4-display-settings' (either from the command-line or from 'Menu'->'Settings'->'Display Settings' will restore everything to it's normal state.

[Skaperen]

so, what does "--panning 3840x2160" do?

i going to set this up on one userid intend to watch 4K videos online.