Compiz has a plugin that previews a window when you put your mouse over its taskbar button. The problem is that it doesn't show up if the window is iconified.

If the window is iconified then there is no window to preview.

I thought that the window still is drawn off-screen when iconified.

That is incorrect. The X server does not draw iconified or shaded windows. Kwin works around this (as, I believe gnome-shell does) by not minimizing windows. Instead, it keeps them active, removes their ability to grab input, and doesn't draw them. There has been some talk in compiz about doing the same thing. The downside being, of course, that some applications act different when minimized. For example, some media players automatically pause if they are minimized. That's not possible in this case as the window is never actually minimized.

Adam

That's kinda sad because it seems like the big advantage of it is to have a preview of a window that's not visible to know you're opening the right one.

Why not at least grab a screenshot of the window before iconification and use it as the preview?

Because doing that is kind of a hack (much like not actually minimizing windows would be a hack).

Adam

It is a bit of a hack, but I think it's far better than nothing.

Well you are more than welcome to contribute the code if you're willing to maintain it :-) Otherwise, you'll have to wait for someone else who is willing (which, actually, may not be too far off).

Adam

It may be worth investigating how the Gnome DockbarX applet does it - as I understand it, when iconified, it 'remembers' the last de-iconified preview, and uses that instead.

wouldn't it be simpler to minimize the window normally. then when a preview is requested (by window previews, ring/shift switcher, scale, etc) restore the window somewhere not directly visible and show the preview of that?

I don't know, maybe it's a good idea. Anyway, I stopped using Compiz a long time ago, then I used KDE4, and it showed a screenshot of the app before it was minimized.

And now I'm using Xfwm4.

I believe M$ Aero actually records screencasts of the windows, even while they're minimized, to display them as previews. Maybe that's what Compiz should do.

It can't because windows don't redraw when minimized, so there's nothing to make a picture of (unless Windows does it differently than X). I still like my idea (and it turns out that's what KWin uses) of taking a screenshot before minimization and using that as the preview.

I know in Windows 7, the thumbnails are still animated when minimized (useful for seeing things like downloads in progress, for example).

Then this must mean windows are just off screen but not minimized, because when a window is really minimized (e.g. in Windows XP), its sizes become 0.