Ugly Horizontal Lines Displayed in Kate and Konsole with Fractional HiDPI Scaling

Upgrading to Qt 5.12 is fine, but does not seem to fix the issue straight away. In Konsole profile settings under the advanced tab, change "Line Spacing" to 1. This has fixed the issue with horizontal lines for me.

This is reported to have been resolved in QTBUG-66036 with version 5.12. As of the time I am writing this, QT on Arch Linux is version 5.11.2-1. Other common distros have also not released packages with Qt 5.12. However, when Qt 5.12 is released, the developers expect this issue to be resolved.

To check your Qt version, you can open a terminal and type:

qmake --version

The output will look similar to this

QMake version 3.1
Using Qt version 5.11.1 in /usr/lib

When you see Qt version 5.12, then you can expect a resolution. If not, let the developers know at QTBUG-66036.

In the mean time, there is a work-around, as described in the bug report below

Steps to reproduce:

1. Displays -> Scale -> Scale Factor: 1.3 (or 1.4, etc.)
2. Restart
3. Open Konsole or Kate, type stuff

Workaround: set Scale Factor back to 1.0 (or to an integer such as 2 or 3).

There is a similar bug report for Konsole here

373232 – Horizontal lines with fractional HiDPI scaling
https://bugs.kde.org/show_bug.cgi?id=373232

As a workaround, you could change the Fonts DPI:

1. go to Fonts, check the box Force Fonts DPI
2. set to an appropriate value (I use 144 on a 2560x1440 screen, you may want to try 192 in 4K)
   • Higher DPI translate to bigger text in your screen
3. Set the your display scaling factor back to 1
4. Logout and login to your user (or restart)

At this point the horizontal lines should be gone and you should be able to read everything on your screen