Things n' Stuff Thoughts about the universe in general

I like to have some kind of slideshow as a desktop background wallpaper, and there are various ways of doing that – using your local picture library or multiple variations of remote image sources (everyone love NASA’s Astronomy Picture of the Day), and you can find a lot of discussions online about how best to go about automating setting the desktop’s background wallpaper image – in KDE Plasma it is particularly not that easy as you have to contend with multiple “activities”, with each has multiple screens, with each has multiple “desktop containments” – fortunately Plasma no longer supports different wallpapers for different virtual desktops – otherwise it would really have been a massive mess.

But sometimes I don’t want to change the wallpaper – just to figure out which one I’m looking it (maybe I want to delete it?). There isn’t any discussion about that on the internet, so I wrote this script and here it is for posterity (and also in this Github Gist):

#!/bin/bash

##
# Helper to find the user configured name of an activity, by its ID
function getActivityName() {
  qdbus org.kde.ActivityManager /ActivityManager/Activities \
    org.kde.ActivityManager.Activities.ActivityName "$1"
}

##
# Helper to list all the currently configured activities by their ID
function listActivityIds() {
  qdbus org.kde.ActivityManager /ActivityManager/Activities \
    org.kde.ActivityManager.Activities.ListActivities
}

##
# Helper to get the ID of the current activity
function currentActivity() {
  qdbus org.kde.ActivityManager /ActivityManager/Activities \
    org.kde.ActivityManager.Activities.CurrentActivity
}

activity="$1" ## allow the user to choose the activity to look at
screen="${2:-0}" ## allow the user to choose the screen to look at
# but default to the first screen, if they didn't specify

grep -qi plasma <<<"$DESKTOP_SESSION" || { echo "Not running under a Plasma desktop!">&2; exit 1; }

# if the user did not specify an activity, use the current one
[ -z "$activity" ] && activity=$(currentActivity)

# if the user specified the activity by name, locate the ID
if [ -z "$(getActivityName "$activity")" ]; then
	activities=( $(listActivityIds) )
	aname="$activity"
	activity=
	for aid in "${activities[@]}"; do
		if [ "$aname" == "$(getActivityName $aid)" ]; then
			activity=$aid
		fi
	done
fi

[ -z "$activity" ] && { echo "Activity '$activity' was not found!">&2; exit 1; }

# The meat of the thing - ask Plasma to run our script
qdbus org.kde.plasmashell /PlasmaShell org.kde.PlasmaShell.evaluateScript "
  var actId = '$activity';
  var scr = $screen;
  var ds = desktops(); // load the containments
  for (let d of ds) { // and walk through them
    // skip any containment that does not match activity and screen
    if (d.readConfig('activityId') != actId ||
        d.readConfig('lastScreen') != scr)
      continue;
    // prepare to read the General configuration (where plugins normally
    // put the current image)
    d.currentConfigGroup = Array('Wallpaper',d.wallpaperPlugin,'General');
    // identify the wallpaper plugin so we can read it properly
    if (d.wallpaperPlugin == 'org.kde.slideshow') {
      print(d.readConfig('Image').replace('file://',''));
    } else if (d.wallpaperPlugin == 'org.kde.image') {
      print(d.readConfig('Image').replace('file://',''));
    } else if (d.wallpaperPlugin == 'org.kde.potd') {
      print('Picture of the Day (Provider: ' + d.readConfig('Provider') +
          ') does not support reading the current image');
    } else {
      print('Unsupported wallpaper plugin: '+d.wallpaperPlugin+'\n');
    }
    break;
  }"

To run this script, create a new text file – I recommend as ~/.local/bin/read-plasma-wallpaper – and paste the script, then give that script execution permissions. When you run it, it will output the full path to the current desktop background wallpaper image to the terminal.

This entry was posted on Monday, March 13th, 2023 at 22:57 and is filed under Articles, Script Day, Software. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.