Some font glyphs are rendered incorrectly (with additional vertical spacing) in GTK applications

[kosheo]

After switching from 16.04 to 18.04 I noticed that fonts are now (in 18.04) rendered differently in GTK+ apps.

For example, there is a vertical bar charcter `│` [U+2502](https://unicode-table.com/en/2502), that is used extensively to create solid vertical lines using just text characters.
You can see it in console apps such as `mc` or `pstree`.
While it is rendered correctly in Terminal in both 16.04 and 18.04, when rendered inside GTK apps it has unexpected vertical gap in-between characters on 18.04 (16.04 renders it correctly).
The issue can be seen in GTK apps such as gVIM, Geany, GEdit, but Qt apps seem to render it properly.

I have attached a screenshot that clearly demonstrates the difference. It shows brand new Ubuntu 16.04 on a left side where you can see vertical line in GEdit is completely solid, as it should be. On a right side it shows Ubuntu 18.04 where you can see line now has gaps that should not be there.

I built a small GTK2 test app that reproduces the problem (sources at https://pastebin.com/WCH1ds4P), and using it I found that the problem occurs when libfreetype 2.8+ is used. I tested FreeType 2.6, 2.7, 2.7.1 and all of them work fine. While 2.8 and above has this gap.

I am not 100% sure if this is an Ubuntu font configuration issue, or bug in FreeType, or GTK or some other Ubuntu components, but I hope someone at least can point me at the right direction.

Please also check my post on AskUbuntu which has additional detail and screenshots: https://askubuntu.com/questions/1054779/incorrect-font-glyphs-rendering-in-gtk-applications-in-ubuntu-18-04

[Ubuntu Foundations Team Bug Bot (crichton)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. It seems that your bug report is not filed about a specific source package though, rather it is just filed against Ubuntu in general. It is important that bug reports be filed about source packages so that people interested in the package can find the bugs about it. You can find some hints about determining what package your bug might be about at https://wiki.ubuntu.com/Bugs/FindRightPackage. You might also ask for help in the #ubuntu-bugs irc channel on Freenode.

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[kosheo (kosheo)]

I added another screenshot that shows how to easily reproduce this issue using pango-view utility.

It also shows the difference in rendering between 16.04 and 18.04.