Plasma always had this really cute concept of “formfactor”: in brief different areas where plasmoids can reside have different behaviours, for instance a desktop is planar, i.e. the applets can grow anywhere they want.
The panel on the other hand can have a vertical or horizontal form factor, it means the applets in it can grow only in the vertical or horizontal direction, so an applet with a high quantity of content can’t display everything it would want…
In past releases of KDE4 the right behaviour of applets was still not really finished, so some applets like the device notifier were more kind to the panel, displaying the whole device list on the desktop and an icon+popup on the panel, other applets like the twitter applet hmm not soo good 🙂
Now with KDE 4.2 every standard applet distributed with kdewill fully use the form factor concept, so far we have 3 different classes of applets:
Applets that are just the same or with very little differences in different form factors, like simple icons or the taskbar.
Applets that diminishes their information quantity in horizontal or vertical form factors, here are two examples:
when in the panel the now playing applet just displays the control buttons, and the leave note applet switches to an horizontal layout, so it makes enough room for an horizontal panel.
Some other applets, like the device notifier or kickoff wouldn’t mean that much without some of its contents, so in the panel will be an icon+popup and in the desktop the whole plasmoid will be shown. but what about very big panels, so big that the whole plasmoid could fit and a ginormous icon wouldn’t make so much sense?
When the applet knows that it would fit into the panel, the icon goes away and the whole applet content is displayed, and goes back to an icon when the panel is shrinked again.
Now, since Plasma in KDE 4.2 supports also panels not always on top and autohide panels, you could have for instance a thing that looks like a Quake console with plasmoids in it, just like Konsole for terminals 🙂
