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

[Michal Suchanek]

DPI is read from the X server, not Xresources.

You can probably adjust DPI by the scale factor in X emulation, Or not
scale emulated X windows as suggested.

Thanks

Michal

On 9 November 2015 at 19:42, Bill Spitzak <spitzak at gmail.com> wrote:
> 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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