Can an app in `/opt/extras` install themeable icons in `/usr/share`?

Question

My application Variety Wallpaper Changer runs from /opt/extras and uses an indicator icon. I would like to make this indicator icon theme-specific. As far as I understand the standard way is to install named icons into /usr/share/icons with xdg-icon-resource at installation time. (Am I right about this?). I have two questions regarding this:

1. Variety installs and runs from /opt/extras.ubuntu.com. Is it acceptable for it to install icons in /usr/share using xdg-icon-resource or is there something else I can do to have theme-specific icons without special-casing themes and dynamically selecting the icon in the code?

2. Variety is packaged using Quickly (and I'm myself a newbie at packaging) - how can I configure it to install theme-specific named icons at installation time?

Answer 1

Generally, the answer is no. According to the Filesystem Hierarchy Standard (FHS), only files that are required to be in a certain location (like lock files and device files) are allowed to be outside of the /opt tree if your software is installed this way.

You are correct in that you can install icons to /usr/share/icons, but again, don't do it if your package installs to /opt. I'm unfamiliar with Quickly, but consider changing your app so it installs to the "usual" places for Linux software: /usr/bin for binaries, /etc for configuration files, /usr/share for data, etc. That way, your icons won't be out of place!