[Gimp-developer] HiDPI/Retina display support and gtk3-port branch?

[Brion Vibber <brion pobox com>]

Hi all!

I'm investigating how well various Gtk-based apps run on hi-dpi displays,
including Apple's "Retina" displays and other vendors' 2560x1440 and above
laptop displays.

Gtk+ 3.10 and later has native support for hidpi display scaling on X11,
Wayland, and Mac OS X backends; on a GNOME 3.10 or 3.12 system if you don't
have a display that triggers the scaling automatically you can switch it in
manually like so:

  $ gsettings set org.gnome.desktop.interface scaling-factor 2

Of course the current Gimp release is Gtk2-based, and on Linux only seems
to see an increased default font size -- many widgets and icons are
displayed at tiny tiny size, so the program is hard to use, but you do get
the full resolution on your actual work image.

Note that on Mac OS X, the situation is a bit different: the current Gtk2
releases display at correct size and most on-screen text is sharp (thanks
to the way Gtk2 sits on top of a native OS X layer that already scales up)
but icons and the actual image graphics are still low-resolution because
the gtk layer knows nothing about the high-resolution backing layer. This
is usable, but makes for an unpleasant experience in that we don't get the
benefit of the high resolution for our pretty graphics!


I did a quick test with the gtk3-port branch on Fedora 20 in scaled mode;
it displays correctly sized and text widgets are nice and high-resolution,
but of course Gimp's own icons are fuzzy and the graphics are
low-resolution (similar to the current OS X state).

Additionally, gtk3-port seems a bit broken. I had to build against a
version of GEGL from a few weeks ago to avoid an error about missing
'gegl:seamless-clone' operation, and the resulting gimp-2.99 runs *really
slow* and constantly pumps a stream of warnings to the console:

  Gdk-WARNING **: gdk-frame-clock: layout continuously requested, giving up
after 4 tries

I'm not sure how much can be done on the gtk2 end (a large icon theme would
probably help on Linux), but I am definitely interested in poking at the
gtk3 branch for proper hi-dpi support. I've gone ahead and filed a bugzilla
entry: https://bugzilla.gnome.org/show_bug.cgi?id=725263

> From asking around in IRC, it seems that the gtk3-port branch won't land on
master until after Gimp 2.10 ships. Should I assume the branch is going to
remain unstable for a while and wait, or is it ok to start doing some
experiments & submitting patches for it?

Thanks!

-- brion vibber (brion @ pobox.com / bvibber @ wikimedia.org)