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

[Bill Spitzak]

Have the X emulator assume the client set the scale to the one determined
from the dpi in the .Xresources?



On Sun, Nov 8, 2015 at 6:10 PM, Jonas Ådahl <jadahl at gmail.com> wrote:

> On Sat, Nov 07, 2015 at 09:48:59PM +0100, Michael Stapelberg wrote:
> > 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.
>
> Pretty much. weston pretty much assumes that X11 clients are simply just
> not HiDPI capable, and will just scale up as if it was a Wayland client,
> and this produces this result.
>
> As a side note, in mutter we currently don't scale up Xwayland client
> surfaces because of this reason; in GNOME, clients tend to be rendered
> with respect to the DPI (i.e. at double the scale if the DPI is high
> enough), and since the X server has no clue about the scale in use, it
> will always set the buffer scale to 1. Pointer cursors has the same
> issue; the X side of things might be aware of it (but without the actual
> X server having any idea of what's going on).
>
> An issue with this is that non-DPI-aware X clients will look very tiny;
> but this since that wasn't really a regression from before, we are
> currently living with it. Another issue is that even though the display
> server is aware of each monitor's individual DPI, X11 windows will not
> adapt their size to the monitor.
>
> A possible way to deal with this in the future is to add per window
> properties specifying the scale the client actually drew its content
> with, an X11 equivalent of wl_surface.set_buffer_scale more or less.
> This might be problematic though because of race conditions and what
> not, and I'm not aware of it being tried out anywhere.
>
> >
> > Shall I file a bug about this, or am I misunderstanding something?
>
> Feel free to report one. I took a quick look, but couldn't see any
> existing bug in the fdo bug tracker which covers this.
>
>
> Jonas
>
> >
> > Thanks,
> > Best regards,
> > Michael
>
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> > wayland-devel at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/wayland-devel
>
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