Subject: 26.3; Emacs icons displaying improperly on KDE

From: xs wang <[email-masked]>
Date: Wed, 22 Jan 2020 15:41:32 +0800

Problem description:

When I use the Task Switcher in the large icon style in KDE plasma, the
Emacs icon is always displayed in low resolution, like in the link below.

https://i.imgur.com/AV4YsN3.png

Steps to reproduce:

1. Install Emacs on Manjaro KDE edition
2. Use the Plasma Large Icons style for the Task Switcher (System Settings
> Window Management > Task Switcher > Main Window > Visualization > Large
icons)
4. Hit alt-tab

Actual results:

The alt-tab window switcher displays Emacs's icon as an ugly scaled-up
48x48 icon as shown in the above picture link.

Expected results:

The 128x128 icon should be used instead, so that the large icon is pretty
and not pixelated.

The problem occurs because Emacs does not set _NET_WM_ICON_NAME to a
128x128 icon. Because of this, the window manager it not aware of the
high-res icon, and is forced to display a scaled-up version of the largest
icon it is aware of--the 48x48 version. This can be verified by running
`xprop` and targeting Emacs's main window; you will see that the largest
icon it knows about is only 48x48.

For more information and context, see the following:
https://bugs.kde.org/show_bug.cgi?id=351055
https://specifications.freedesktop.org/wm-spec/1.4/ar01s05.html

The same problem have been discussed several times in the reddit, see:
https://www.reddit.com/r/emacs/comments/czhs57/the_emacs_icon_is_pixelated_in_plasma/
https://www.reddit.com/r/kde/comments/cnyuzw/some_icons_in_alt_tab_switcher_are_pixelated_for/