One of the changes to the Plasma workspace in Plasma 5 (based on KDE Frameworks 5) and continued in Plasma 6 (based on KDE Frameworks 6) is that the option of having separate Plasma widgets on each virtual desktop is no longer available. This is unfortunate, because one useful side effect of being able to do that was the ability to have different desktop backgrounds (wallpaper) on different virtual desktops, so proving a useful visual cue as to the desktop currently displayed.
The most relevant KDE bug is https://bugs.kde.org/show_bug.cgi?id=341143
The position of the Plasma developers, as stated in the evaluation of that bug, is that there have been major architectural changes within Plasma and at the moment the option is not available, with no simple way to bring it back. It has been acknowledged as an omission and is currently being worked on. Please be considerate to the developers and refrain from commenting on the bug unless you really do have a useful contribution to make to the discussion.
This system tray application attempts to being back the ability to have different wallpapers on different virtual desktops, pending the feature being reintroduced into Plasma. It allows a wallpaper image file (or, see below, a video file) to be configured for each virtual desktop, and will change the background when the virtual desktop changes. It does this by changing the wallpaper image settings, so there is some Plasma configuration needed in order to use it. See below for instructions on how to do that.
The application is built and installed in much the same way as any other KDE application. Assuming that you have Qt 6, KDE Frameworks 6 and the Plasma desktop installed, go to a suitable build location (e.g. your home directory) and do:
git clone https://github.com/martenjj/wallpaperswitch.git
cd wallpaperswitch
git switch kf6
mkdir build
cd build
cmake ..
make
sudo make install
Building requires CMake and also KDE Frameworks development headers and libraries. Depending on your distro, you may need to install additional packages for these. If you are running Kubuntu then see the README.kubuntu file for a list of packages required.
After the files are installed above, start the switcher either from whichever desktop launcher you use (it will appear in the "Utilities" category), or by typing the command 'wallpaperswitch' in a terminal or KRunner (summoned by typing Alt-F2). The "desktop" icon will appear in the system tray. If you set the "Start automatically on desktop startup" option on in the settings, the switcher will start automatically when the Plasma desktop starts.
If this is the first time that the application has been run the the configuration dialogue will appear automatically. Otherwise, click the right mouse button over the system tray icon and select the "Configure..." option from the menu. Turn on the "Enable the desktop wallpaper switcher" check box if necessary.
Each currently configured virtual desktop will be listed there. To select the wallpaper image for a desktop, double click the entry or select it and click the "Set Wallpaper" button. From the file dialogue that appears, choose an image file (or a video file, see below). Repeat the same for each virtual desktop or, if you have more than one screen, each screen for each virtual desktop.
Click the "Plasma desktop settings" link at the bottom right, and follow the instructions there to set the required desktop settings. Then finally click "OK" to save the configuration.
The wallpaper image that you selected for the current virtual desktop should now appear, and change when the virtual desktop changes.
Switching can be enabled or disabled using the "Enable Switching" option on the system tray popup menu.
As well as a still image, a video file (MP4, MKV, WebM, MOV and other common formats) can be selected as the wallpaper for a virtual desktop. Plasma cannot show a video as the desktop background by itself, so a wallpaper plugin which can do so is provided with this application and is installed along with it - nothing else needs to be installed and no wallpaper settings need to be changed. See "Transitions between wallpapers" below for what it does and why.
Still images and videos can be mixed freely between virtual desktops and screens. Set them in exactly the same way, using the "Set Wallpaper" button; video files appear in the file dialogue alongside the image files.
The "Smart Video Wallpaper Reborn" plugin,
https://github.com/luisbocanegra/plasma-smart-video-wallpaper-reborn
can be used for videos instead, see "Transitions between wallpapers" below. In that case, that plugin keeps a list of videos together with their individual settings (playback rate, looping and so on). Setting a video as the wallpaper adds it to that list if it is not already there, leaves only that video enabled, and does not disturb any settings that have been made for the other videos in the list. This means that per-video settings can still be adjusted in the plugin's own configuration dialogue and they will be retained. If a fork or a compatible successor of that plugin is installed under a different plugin ID, then set that ID as the "videoWallpaperPlugin" key in the "[Wallpaper]" group of the "wallpaperswitchrc" configuration file.
A video is shown in the configuration list as a thumbnail of its first frame. Generating that needs a video thumbnailer to be installed, the usual one being "ffmpegthumbs" (the package is called that on Kubuntu and most other distributions). If there is none installed then a generic video icon is shown instead.
Plasma destroys the old wallpaper as soon as a new wallpaper plugin is loaded (see ContainmentItem::loadWallpaper() in libplasma), and there is no transition between one plugin and another. So if the standard "Image" plugin were used for images and a video plugin for videos, the desktop would go blank for as long as the new wallpaper took to load every time the virtual desktop changed between the two sorts.
To avoid that, a wallpaper plugin called "Image or Video (Wallpaper Switcher)" is provided with this application and is installed with it. It shows both images and videos, so the wallpaper plugin never has to be switched. It keeps two layers, loads the incoming wallpaper into the hidden one, and only starts to fade once that layer reports that it has something to show - so the desktop never goes blank, whichever sort of wallpaper is being changed from or to.
This plugin is used automatically if it is installed, and it does not need to be selected as the wallpaper type by hand.
The transition used when the wallpaper changes is selected in the configuration dialogue of the switcher application: a fade, an immediate change, a slide in any of the four directions, or a zoom in or out. The duration can be set there to anything between zero and 5 seconds, the default being 350 milliseconds. Whatever the transition, the new wallpaper is always fully loaded before it starts, so the desktop never blanks.
The remaining settings of the plugin are in the Plasma wallpaper settings, and can be changed there while it is selected as the wallpaper type:
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The positioning and the background colour.
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When the video is paused, and when it plays at a reduced speed. Both can depend on the windows on the current virtual desktop: whenever there is a maximised or full screen window, whenever any window has the focus, or whenever any window is visible at all. There is no point in decoding a video which is covered up, and the default is therefore to pause it while a maximised or full screen window is in front of it.
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When the wallpaper is blurred, which can depend on the same window conditions, or whenever the video is paused, or always. The blur radius and how long the blur takes to appear can be set.
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What to do when running on battery and the charge has fallen below a given percentage: pause the video, stop blurring, or both.
The video sound (which is muted by default) is also there.
How long the change takes is the time to load the new wallpaper, plus the transition. The loading time only applies the first time that a wallpaper is shown: a wallpaper is not released when it is changed away from, so changing back to it - as when moving between two virtual desktops - starts immediately. Playing a video needs the QtMultimedia QML module, which is packaged as "qml6-module-qtmultimedia" on Kubuntu and similarly on other distributions.
Setting "useMediaPlugin" to false in the "[Wallpaper]" group of the "wallpaperswitchrc" configuration file goes back to using the standard "Image" plugin for images and "Smart Video Wallpaper Reborn" for videos, with the blanking described above. The video plugin can fade between one video and the next if its "Crossfade" option is turned on, but there is nothing that can be done about changes between an image and a video.
If you are able to build and install the application, but it will not run or it is not able to change the desktop background, then try starting it from a terminal window within the Plasma desktop. Observe the debugging messages for anything about missing files or any other problems.
If this does not indicate the problem then please raise an issue in GitHub (http://github.com/martenjj/wallpaperswitch). Do not raise a bug against KDE Plasma.
The original wallpaper switch for Plasma 5 (branch 'master' in this repository) no longer works because of changes to the Plasma desktop slideshow plugin (commit ea32a761 to plasma-workspace).
If you are using Plasma 5 and wish to have different wallpaper images per virtual desktop, then I suggest that you install the "Vallpaper" plugin and set it as the desktop background. Its configuration dialogue will then allow you to select an image file (or multiple images) for each virtual desktop. You can obtain this plugin via GitHub, or by using the "Get New Plugins" button in the desktop configuration dialogue. I have no connection with Vallpaper, apart from being able to report that it appears to work well and does exactly what it says. Unfortunately it does not yet appear to have been updated for Plasma 6.
If you use virtual desktops and want wallpaper switching then I hope that this utility will come in useful, and also that one day it will not be necessary...
Jonathan Marten, http://github.com/martenjj