[xmir] Dialogs/fonts are scaled way too big

[Ken VanDine]

Testing out the gimp on my flo, some pretty basic use cases are unusable. Attempting to export the image as a png shows the dialog that I attached to the bug. The font is huge, buttons are huge and not all the buttons and options are even on the screen.

[Christopher Townsend (townsend)]

The version of xmir in ppa:libertine-team/devel fixes this issue. Leaving this open until a new version of xmir is in the overlay PPA.

[Daniel van Vugt (vanvugt)]

Wait, did I fix this or someone else? And where?

[Daniel van Vugt (vanvugt)]

AFAIK, we have not done anything that changes scale or DPI in Xmir. So this is possibly not an Xmir bug at all. Something wrong with the launcher/config/environment instead.

[Daniel van Vugt (vanvugt)]

Is there any way to reproduce this without Libertine? I've never seen it happen myself.

[Daniel van Vugt (vanvugt)]

I think it's likely we need to involve other packages/projects in this bug. I'm not sure how Xmir itself could be involved other than here:

Xmir reports the physical display dimensions from Mir through XRandR:

$ xrandr
Screen 0: minimum 320 x 200, current 1920 x 1200, maximum 32767 x 32767
VGA-0 disconnected
DP-0 disconnected
HDMI-0 disconnected
DP-1 disconnected
HDMI-1 disconnected
DP-2 connected 1920x1200+0+0 520mm x 320mm
   1920x1200@60.0Hz 59.88*+
DP-3 disconnected

However (by design) if you are using non-rootless mode and happen to resize the root window then those physical display dimensions are removed. Apparently because the root window no longer relates to a physical output any more:

$ xrandr
Screen 0: minimum 320 x 200, current 1612 x 1055, maximum 32767 x 32767

So it's possible that clients like GTK might get confused by the loss of the display information with which to calculate the output DPI. Just a wild guess...

[Daniel van Vugt (vanvugt)]

Waaait a minute... Is it Mir just reporting junk screen dimensions on 'flo'? Does anyone have a flo and able to tell me what the output of 'mirout' is?

[Christopher Townsend (townsend)]

As a data point, everything looks fine when using a Libertine chroot on a *desktop* system based on Vivid+overlay. I only see this on my N4, so it seems specific to either arm or the phones themselves or both.

[Christopher Townsend (townsend)]

And another data point is that the scaling issue did not occur on my N4 when using Xmir from https://launchpad.net/~libertine-team/+archive/ubuntu/devel/+packages.

As a matter of fact, I downgraded xmir to the version in the libertine PPA and the scaling issue no longer occurs, so I'm pretty sure this is an Xmir issue on arm.

[Christopher Townsend (townsend)]

Just to be clear, this was seen originally in version 2:1.17.2-1ubuntu0.1~overlay5 from the overlay PPA. The issue goes away in version 2:1.17.2-1ubuntu0.1~overlay5+ppa1 from the libertine PPA. And the issue is back again with version 2:1.17.2-1ubuntu0.1~overlay6 from the overlay PPA.

[Christopher Townsend (townsend)]

Ok, another interesting data point. If I use '--rootless --flatten' and remove Compiz from the equation, then scaling is fine, so it seems it's specific to non-rootless on arm.

[Daniel van Vugt (vanvugt)]

Reproduced. The issue appears to be:

(gimp:20084): Gimp-Widgets-WARNING **: GDK returned bogus values for the screen resolution, using 96 dpi instead.
(gimp:20084): Gimp-Widgets-WARNING **: GDK returned bogus values for the screen resolution, using 96 dpi instead.

which sounds wrong for two reasons:
  1. Even after working around #6, xrandr reports valid dimensions (61mm x 102mm)
  2. If gimp/GDK really is falling back to 96 dpi then fonts would not appear large at all. They would appear normal (too small).

[Daniel van Vugt (vanvugt)]

Hmm this is probably it...

$ xdpyinfo
...
screen #0:
  dimensions: 768x1222 pixels (0x0 millimeters)
  resolution: 2147483647x2147483647 dots per inch

[Daniel van Vugt (vanvugt)]

And fixed.

$ xdpyinfo
...
screen #0:
  dimensions: 768x1222 pixels (61x97 millimeters)
  resolution: 320x320 dots per inch

https://git.launchpad.net/~xmir-team/xorg-server/+git/xmir/commit/?id=82c297b651c4bc45ad6ec591aae33280df3c726b

[Daniel van Vugt (vanvugt)]

Also, GIMP is still buggy. It's fallback to 96 DPI is clearly broken but with Xmir fixed we can hopefully avoid needing to fix GIMP.

[Daniel van Vugt (vanvugt)]

Fixed rootless too:
https://git.launchpad.net/~xmir-team/xorg-server/+git/xmir/commit/?id=cb043eb35dbd2a8c418f328396b882be31de4cab

Warning:
Now the bug is fixed you're still going to see some (significant but no longer absurd) font size differences between apps because the apps themselves are actually quite different. Gimp and Firefox honour the screen DPI and will scale up for the phone screen (less so than before the bug was fixed). However other simpler GTK apps don't bother and will appear very small still. This is down to the apps themselves being well written for high-DPI or not.

If in doubt, check 'xdpyinfo' to see what the physical screen dimensions being reported by Xmir are.

[Daniel van Vugt (vanvugt)]

xorg-server (2:1.17.3-2ubuntu2) xenial; urgency=medium