The transition wallpaper does not have right scale on HiDPI monitor.

[Kai-Heng Feng]

Ubuntu Release: 16.04
Package Version: 16.04.0-0ubuntu1

What you expected to happen:
    The wallpaper scales to whole HiDPI monitor.

 What happened instead:
    The wallpaper only shows on upper left corner.

[Sebastien Bacher (seb128)]

Great work Kai, thanks for looking to that bug, the fix seems to work nicely!

@Artur, why did you nominate for trusty? I don't think we have hidpi working in that Ubuntu serie at the moment so the bug shouldn't impact it

[Sebastien Bacher (seb128)]

Ok, after talking to Shih-Yuan there are still plans to backport some of the hidpi work to trusty so it might become relevant for that serie, accepting the nomination

[Shih-Yuan Lee (fourdollars)]

@Sebastien, thanks.

[Kai-Heng Feng (kaihengfeng)]

Hi Sebastien,

When we enabled OEM products with HiDPI display, the "let's wait before xsettings settle down" hack was applied [1], so the unity-greeter is actually scaled to the right resolution, hence this issue.

So it would be great if this fix can be put into Trusty.

[1] https://bazaar.launchpad.net/~fourdollars/unity-greeter/add-hidpi-support/revision/1497

[Launchpad Janitor (janitor)]

This bug was fixed in the package unity-greeter - 16.04.1-0ubuntu1

---------------
unity-greeter (16.04.1-0ubuntu1) xenial; urgency=medium

  * New upstream release:
    - Fix background after login being scaled incorrectly (LP: #1557893)

 -- Robert Ancell <email address hidden> Fri, 18 Mar 2016 09:46:32 +1300

[Kai-Heng Feng (kaihengfeng)]

In order to make the change build-able on Trusty, we need to add new interface into cairo.vapi:

--- vala-0.22-0.22.1.orig/vapi/cairo.vapi
+++ vala-0.22-0.22.1/vapi/cairo.vapi
@@ -645,6 +645,8 @@ namespace Cairo {
                public void mark_dirty_rectangle (int x, int y, int width, int height);
                public void set_device_offset (double x_offset, double y_offset);
                public void get_device_offset (out double x_offset, out double y_offset);
+ public void set_device_scale (double x_scale, double y_scale);
+ public void get_device_scale (out double x_scale, out double y_scale);
                public void set_fallback_resolution (double x_pixels_per_inch, double y_pixels_per_inch);
                public void show_page ();
                public Status status ();

Those two functions are indeed in Trusty's cairo, so I think it's safe to expose these interface for Vala.