Xwayland and weston’s scale=2 (hi-dpi display)

[Michael Stapelberg]

Hey,

I just got around to trying Wayland on my ThinkPad X1 Carbon 2015.

The machine has a 2560x1440px display with 220 DPI, hence I’m using it as a
“retina display”, i.e. with a scale factor of 2. On Xorg, I achieve this by
setting “Xft.dpi: 192” in my ~/.Xresources. All the applications then come
up with crystal-clear text, in comparison to a regular 96 dpi screen at
least… :)

When running weston without a ~/.config/weston.ini, everything is rendered
with the native resolution of 2560x1440px, meaning the text is unreadably
small (see the left weston-terminal window in
http://t.zekjur.net/xwayland-scale-1-x.png).

Therefore, I’ve set the following in my ~/.config/weston.ini:

  [output]
  name=eDP-1
  scale=2

This is recommended on
https://wiki.archlinux.org/index.php/Wayland#High_DPI_displays, but I’m not
sure if it’s actually the best method or the desired end state of hi-dpi
support in wayland/weston. My uncertainty stems from the fact that while
text in weston-terminal is rendered clearly, all assets (icons, mouse
cursors) are low-resolution, even though higher-resolution versions are
available.

For the actual issue I’m trying to describe, my test procedure is to use
“xrdb ~/.Xresources && urxvt”, then place the urxvt window such that it
occupies about half of the screen.

With scale=2 (see http://t.zekjur.net/xwayland-scale-2-x.png), I get a
window with about 640px width in xwininfo and an extremely big font. I
suppose this is because the Xwayland window (is that how it works?) is
scaled to 2x.

With scale=1 (see http://t.zekjur.net/xwayland-scale-1-x.png), I get a
window with about 1280px width in xwininfo and the font I expect.

So, it seems to me that I have to use scale=2 to get wayland apps to render
correctly on a hi-dpi screen, and scale=1 to get xwayland apps to render
correctly on a hi-dpi screen, and I obviously can’t do both at the same
time.

Shall I file a bug about this, or am I misunderstanding something?

Thanks,
Best regards,
Michael
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