This patch adds support for observing multiple slices of the desktop background.
This is used for the tray so that it doesn't have to rely on the bar's rect to
get the desktop background. In particular, it now handles the case where the
tray is not contained fully within the bar's outer rect (for example, when using tray-offset-{x,y})
Co-Authored-By: bennofs <benno.fuenfstueck@gmail.com>
The systray only supports pseudo transparency (real transparency would require
much larger changes) so the real transparency should only be used for the bar itself.
We now take the bar position that the window manager gives us instead of trying
to calculate it ourselves. This is more correct when multiple bars are attached
to the same edge, as the window manager may move some of them in that
case (assuming override redirect is not enabled)
