I wanted to do something dead simple, make my KDE4 task manager show only the current desktop windows. I found out it a bit tricky, I kept trying right clicking the task bar to get its settings, only to end with “Panel Settings” which is the whole plasma panel settings menu, until I figured out the easiest way to do it:

1- Click on the “Cashew” icon of the plasma panel  ( check the screenshot )

snapshot_1

2- Right click on the task bar, BINGO, here u find out the task bar settings menu

snapshot_2

3- Check the “Only show tasks from the current desktop” check box. Voila

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Enjoy !