I've recently made the switch to Ubuntu 19.04 with KDE plasma. First off, congrats to all the folks out there that have made Linux usable to a computer user, not a professional. With little effort I was able to leave the Windows world and save myself a lot of headache. Now, my problem. 3 monitors, one is a 4K television with resolution sized to replicate 4 monitors though it is only recognized as 1 big monitor while I have two normal 1600x900 monitors to the right. Problem, when a new dialog, notification or program opens it is always in the far left upper corner of the 4k tv. I would prefer they open in the center monitor and I will move them if necessary. I've searched and searched for an answer so if this has already been asked please forgive, I couldn't find it.
11/23/19 Updated computer info: Homebuilt, Intel i5-4690, 4 core, 3.50GHZ; graphics card Intel HD 4600, NIC, sound all on motherboard; 16GB ram; 1TB HD; Kubuntu 19.04; standard monitors x2 are HP W2071d; tv monitor LG 43uk6300pue 4096x2160. Let me know if you need any more info. Thanks.
11/24/19 Update: The middle monitor has been set to primary all along but it didn't seem to affect the problem. The tv monitor is on the left, the 20" HP's are middle and right.
11/27/19 Answered Thanks Kenneth, that did the trick. System settings - Window Behavior - Advanced - Placement - Centered; new notifications, pdfs etc. open in center of window where application is. I only tested it with a few instances of each so longer term experience will be necessary. Obviously there is a tremendous amount of possible customization if I use "Window Rules" or "Kwin Scripts" but that is out of my pay grade. I just want convenient.
12/4/19 Update Additional info - Some windows need to be individually set to open where you want them, the above solution seems to be a bit hit or miss. Windows still open elsewhere but only a few with no real rhyme or reason. But notifications and most windows now open centered on the primary monitor.
22 Answers
I'm not fully sure. But in the display configuration try setting the middle monitor, on which you wish to see notifications/dialogs, to the "Primary display".
I don't think it is possible to do what you are asking (at least, not with the system settings menu), but you may be able to at least improve things somewhat.
At the very least, you should be able to get windows to open in the center of the "active" monitor, even if this is not always the middle monitor. Take a look at the settings under Window Management > Window Behavior. In particular, try playing with the options under "Multiscreen Behavior" on the Focus Tab, and the "Placement" option on the Advanced Tab.
Apparently the "primary monitor" setting that you already tried has more to do with panel placement than window placement.
It may be possible to get exactly what you want using KWin rules, though there may be undesired side effects. See this Reddit post.
