My various settings in X to get programs working on my HiDPI display
Back when I got my HiDPI display (a 27" Dell P2715Q), I wrote an entry about what the core practical problems with HiDPI seemed to be on Linux and talked in general terms about what HiDPI related settings were available but I never wrote about what specific things I was setting and where. Today I'm going to remedy this, partly for my own future use for the hopeful future day when I need to duplicate this at work. Since I'm doing this two years after the fact, there will be an exciting element of software archaeology involved, because now I have to find all of those settings from the clues I left behind in earlier entries.
As mentioned in my old entry, the Dell P2715Q
is a 163 DPI display. To make the X server itself know the correct
DPI, I run it with a '
-dpi 163' command line argument. I don't
use XDM or any other graphical login manager; I
start the X server from a text console with a nest of shell scripts,
so I can supply custom arguments this way. I don't do anything with
xrandr, which came up
with plausible reported screen dimensions of 597mm x 336mm and didn't
appear to need any changes.
I use xsettingsd as my
XSettings daemon, and set two DPI related
Gdk/UnscaledDPI 166912 Xft/DPI 166912
Both of these values are my 163 DPI multiplied by 1024. For Xft/DPI, this is documented in the Xsettings registry. I'm not sure if I found documentation for Gdk/UnscaledDPI or just assumed it would be in the same units as Xft/DPI.
There is also an X resource setting:
As we can see, this is just the DPI.
Then I set some environment variables, which (in 2018) came from Arch's HiDPI page, the Gnome wiki, and the GTK3+ X page. First there is a setting to tell Qt apps to honor the screen DPI:
Then there is a pair of GTK settings to force GTK+ applications to scale their UI elements up to HiDPI but not scale the text, as explained in more depth in my original entry:
export GDK_SCALE=2 export GDK_DPI_SCALE=0.5
These three environment variables are only necessary for Qt and GTK+ applications, not basic X applications. Basic X applications seem to work fine with some combination of the Xft.dpi X resource and the XSettings system.
If you're running remote X applications from your HiDPI X session, as I am these days, they will automatically see your Xft.dpi X resource and your XSettings settings. They won't normally see your (my) specially set environment variables. Fortunately I mostly run basic X applications that only seem to use X resources and perhaps XSettings, and so basically just work the same as your local versions.
(At least after you fix any problems you have with X cursors on the remote machines.)
At the moment I'm not sure if setting the environment variables for
remote X programs (for instance by logging in with '
setting them by hand, and then running the relevant program) works
just the same as setting them locally. Some testing suggests that
it probably is; while I see some visual differences, this is probably
partly just because I haven't adjusted my remote programs that I'm
testing with the way I have my regularly used local ones (after
all, I normally use them on my work regular DPI displays and hopefully
some day I'll be doing that again).
The final setting I make is in Firefox. As mentioned in passing in
this entry, I manually set the
layout.css.devPixelsPerPx to 1.7, which
is down from what would be the default of '2' based on my overall
settings. I found that if I left Firefox alone with these other
settings, its font sizes looked too big to me. A devPixelsPerPx
setting of 1.7 is about right for what the Arch Wiki Firefox
suggests should be correct here, and it looks good to me which
is what I care about most.
Sidebar: X resources tweaks to specific applications
Xterm sizes the width of the scrollbar in pixels, which isn't ideal on a HiDPI display. It is normally 14 pixels, so I increased it to:
Urxvt needs the same tweak but it's called something different:
I think I also tried to scale up XTerm's menu fonts but I'm not sure it actually worked, and I seem to have the same X resource settings (with the same comments) in my work X resource file.