tray icons: fix the 'black hole'

[joanna]

We should really use the tray's background instead of the _ugly_ black background for displaying tray icons from AppVMs!

[smoku]

Implemented in: ​http://git.qubes-os.org/?p=smoku/gui;a=commit;h=35647b9eb54c689e81aa5b9bdd4ab60fc1de41d2

Some comments though:
I do not have full alpha channel available. I do not even have any transparency info. So I assume that the color of the top-left pixel of the tray icon is a transparent color, then generate transparency mask accordingly.

It creates an issue with alpha blended (antialiased) icons. They are blended to vmside root window, which is black. This creates even more ugly "shadow" around the icon.

My idea to mitigate it is:

• set the docked icon background to the VM color (as Joanna wished anyway)
• xsetroot -solid VM_COLOR on the vmside

This blends the icon to the color of the VM and paints on the same color background, which does not look ugly.

[joanna]

I have never wished to set the icon's background to the VM color (I said we could repain the icon in "grayscale" colored to the VM color) -- this not only looks bad, but is also insecure, as the AppVM controls the background!

[joanna]

If nothing better was possible, we could just set the bgd of the parent (root) window to white. And still draw the frame in Dom0 around the icon using the VM.color.

[joanna]

Set bgd to white in the VM. I think white is the safefest color, assuring most icons would just look good. Or some light gray.

[joanna]

Actually the tray icon (as of v1.2.1) is transparent to _Dom0_ root window, not to VM root window. I.e. if I move a window in Dom0 beneath the tray, I can see it through the icon's bgd.

[smoku]

White tray and vm background implemented in: ​http://git.qubes-os.org/?p=smoku/gui;a=commit;h=329128f313738c42c5a7a21638c13855cff7b23a