>> https://phabricator.kde.org/D12405#251159 > >> graesslin.Apr 21 2018, 7:01 PM >> I also cannot imagine this to work due to the fact how X11 works. There is >> just no mapping from window to screen. No window can know on which screen it >> is. Not even KWin knows that as the window manager (screen is not a constant >> property, but evaluated every time it is accessed, it's based on the >> distance to closest screen). Especially for overlapping windows it's very >> difficult to try to get to which screen it belongs. It gets even more >> complicated when things like panning and overlapping screens get into it. So >> I wouldn't trust this thing in Qt to work due to the pain we have in KWin >> especially with these problems.
On 01/08/18 12:33, Bruno Pagani wrote: > OK, then maybe you’ve just stumbled upon one of the numerous HiDPI Qt bugs… Which brings me back to the original post. If I could figure out how to do it this way, https://blog.summercat.com/configuring-mixed-dpi-monitors-with-xrandr.html because that sounds like it would avoid this problem. > The tricky parts > > There were two aspects I found problematic: > > First, the fact that the two monitors have differing DPI means each monitor > needs different settings to account for that. xrandr allows setting the DPI > via --dpi, but this applies globally to all monitors. I dealt with this by > setting the global DPI to that of the highest DPI monitor, and then used > --scale to adjust the lower DPI monitor. > > Second, switching back and forth between dual monitors to one monitor lead to > interesting behaviour. For example, I kept losing the scale setting on the > lower DPI monitor. Previously on the list ProgAndy said: > The panning option might be there as a workaround for a bug in xorg. > Since xorg 1.20 the patch to resolve that should be included, so you can try > your configuration without panning. I feel he might be right based on the results I had with xrandr --output eDP1 --pos 5120x0 --auto \ --output DP1 --pos 0x0 --auto --scale 2x2 > I had a semi-working setup with little trouble, but it involved restarting X > when I wanted to switch between dual and single monitors. This worked, but > obviously was inconvenient. I wanted a solution that would work without > restarts. I do think he might be right. It does seem like it might be also a workaround for this Qt5 issue. >From that blog post: > Single monitor (external) > > If I want to use only the lower DPI monitor, then I run this command: > > xrandr --dpi 276 --fb 3840x2160 \ > --output eDP-1 --off \ > --output DP-1-2 --scale 2x2 --panning 3840x2160 > > Most of these options are similar to the first command's. The main difference > is disabling the laptop monitor with --output eDP-1 --off. > > Note 3840x2160 comes from 1920*2 x 1080*2. > > You might wonder why I set high DPI and scale the lower DPI monitor here. > Wouldn't it be simpler to set a lower DPI and use the monitor's native > resolution? That's possible, but since I've configured other things (such as > my X terminal fonts) to a size suitable for a high DPI screen, I'd have to > adjust settings elsewhere. Keeping the DPI the same and continuing to scale > allows me to avoid that. Since I'm scaling, I need to configure a large > screen and set panning for the same reasons as before. I was able to get that working using my numbers for the Dell 30" 3008WFP xrandr --dpi 220 --fb 8960x5360 \ --output eDP1 --mode 3840x2160 --pos 5120x0 \ --output DP1 --scale 2x2 --pos 0x0 --panning 5120x3200+3840+0 However with the Dual Monitors not so much; > Dual monitors > > When I want to use both monitors, this is the command I run: > > xrandr --dpi 276 --fb 7040x3960 \ > --output eDP-1 --mode 3200x1800 \ > --output DP-1-2 --scale 2x2 --pos 3200x0 --panning 3840x2160+3200+0 > > Here's an explanation of the options: > > Global options: > --dpi 276 sets the DPI to 276. > --fb 7040x3960 creates one screen with resolution 7040x3960. This is > the combined resolution of the two monitors. The high DPI monitor has > 3200x1800 resolution. The lower DPI monitor has 1920x1080 resolution, but I > double it as I scale it by 2 (see below). Combine these like so: 3200+1920*2 > x 1800+1080*2 = 7040x3960. Both monitors share this screen. > High DPI monitor options (--output eDP-1): > --mode 3200x1800 says to use resolution 3200x1800. This is the > default, but specifying it is necessary if the monitor is disabled (as it is > when using the external monitor by itself) as it enables the monitor. > Lower DPI monitor options (--output DP-1-2): > --scale 2x2 is similar to zooming out. This is necessary as we set > the DPI globally to that of the high DPI monitor. > --pos positions it to the right of the laptop monitor. > --panning allows our pointer to access the whole area. Using the numbers I calculated: eDP1 (30" @ 2560x1600) DP1 (13.3" @ 3840x2160) 3840+2560*2=8960 2160+1600*2=5360 xrandr --dpi 220 --fb 8960x5360 \ --output eDP1 --scale 1x1 --mode 3840x2160 --pos 5120x0 \ --output DP1 --scale 2x2 --pos 0x0 --panning 5120x3200+3200+0 using that I am seeing https://i.imgur.com/gTAsRUe.jpg which is a bit strange but getting closer. I think i am messing up the last part of panning the +3200+0 bit. Eric.. You have a very similar setup, to me. I shall give that a try soon. -- Tyler
