Rendering issues under Wayland with a Mixed DPI setup

[Aryan Ameri]

Hi,

Running Ubuntu Gnome 16.10 Yakkety with Wayland. 

I have a "Mixed DPI" setup with two monitors, one of which is high resolution
and requires DPI scaling set to 2, the other one has a normal resolution and
doesn't require DPI scaling. To be clear, this is a Macbook Pro with Retina
display, where the laptop's screen is high resolution, but it's connected to a
2560x1080 external monitor which doesn't require DPI scaling. 

macOS handles this well, setting the DPI scaling automatically for each monitor,
and applications also adapt seamlessly when moved from one to the other. X never
had any notions of a mixed DPI scaling so under X, I really could only use one
or the other monitor. Gnome 3 with Wayland comes close to properly handling it,
but it does suffer from some rather strange rendering problems: 

1) Menus in some GTK applications (including some default Gnome applications)
open at incorrect place. So if I click on the "File" or "Edit", the menu doesn't
show up where it should, instead it shows up half way down the screen. 

Notice for example in this screenshot where the "File" menu of Evolution opens. 

Screenshot 1: http://imgur.com/a/HiwAN

This problem is also present with the right-click menu in these applications. 

2) Some other applications, such as Firefox, do not have the above issue but
instead suffer from other issues, namely: 

a) The mouse cursor is huge while it hovers over the application's window. It
goes back to its normal size when the mouse goes outside that window. 

In these two screenshots, compare the size of the mouse when it's inside
Firefox's window to when it's outside it

Screenshot 2: http://imgur.com/a/DBnWL
Screenshot 3: http://imgur.com/a/12ycW

b) The same applications have a huge title bar. The title bar both takes up a
lot of vertical space, as well as uses too big a font. Refer to the previous two
screenshots to compare Firefox's title bar with that of Gnome Terminal for
example. 


3) Some other applications do not follow the correct DPI scaling at all. For
example in this screenshot, compare GIMP with Epiphany (the latter adjusts DPI
scaling correctly) 

Screenshot 4: http://imgur.com/a/f4Jn5

This problem exists amongst many other applications such as Chromium, as well as
qt-based applications. 

Are these issues known? I tried looking up but my google-fu might have failed
me. If these bugs are not known, I'd be happy to file bug reports but the
problem is I don't know where the problem lies and who the appropriate upstream
is. Is it an issue with Wayland? Gnome? Ubuntu? The GTK and Qt toolkits? 

Cheers
-- 
Aryan Ameri