Comment 15 for bug 1159430

I investigated a bit more. Compiz performs compositing via the Composite plugin, found in plugins/composite. The code there does check for desktop windows (i.e. of type _NET_WM_WINDOW_TYPE_DESKTOP) and prevents them from being transparent. I removed those checks so that all windows can be transparent and rebuilt Compiz. (I'll attach a patch with those changes in case anyone else wants to try this out.) With those changes, I ran a small test program which shows that a window of type _NET_WM_WINDOW_TYPE_DESKTOP does appear transparent over Compiz wallpaper, i.e. the changes worked. But unfortunately when I ran Nautilus and a Compiz wallpaper plugin together, I still saw only the Compiz wallpaper, not the Nautilus icons. Perhaps this is a z-ordering problem, i.e. the Nautilus window is behind the wallpaper. Or maybe something else is going on.

It would also be interesting to try to make this work with gnome-settings-daemon's background plugin drawing the wallpaper. That might require a couple of changes to the background plugin code. Currently that plugin checks whether Nautilus is displaying a desktop window and declines to draw the background in that case, so we'd need to change that. Also, from glancing at the code it appears that that plugin doesn't set its own window to type _NET_WM_WINDOW_TYPE_DESKTOP. Maybe it would need to for this to work; I'm not sure.