[Bug 40828] Switching resolution in desktop mode makes task bar redraw on top of full screen game

[wine-bugs at winehq.org]

https://bugs.winehq.org/show_bug.cgi?id=40828

--- Comment #14 from Olivier F. R. Dierick <o.dierick at piezo-forte.be> ---
Created attachment 63192
  --> https://bugs.winehq.org/attachment.cgi?id=63192
other way to fix issue

Hold on.

Hamish Claxton's efforts at fixing the issue awakened my interest into it.
I reviewed his patches and thought that there was room for improvements.
So I dug into the code base and ended with another approach:

The visibility of the taskbar is handled by do_hide_systray() and
do_show_systray(). Those functions are called at certain events.
do_show_systray() calls SetWindowPos() with HWND_TOPMOST and without
SWP_NOZORDER. That causes the taskbar to be pushed on top of the window stack
when do_show_systray() is called. Since WM_DISPLAYCHANGE calls
do_show_systray() the taskbar comes to the foreground when the resolution
changes.

Now for the fix: At first I thought about putting a condition when there is a
fullscreen window in the foreground, as Hamish Claxton wanted to do, but I
remembered that wine already hides the taskbar when a fullscreen window is open
(the issue happens only when resolution changes). So I looked at how this was
achieved. It actually amounts to a simple matter of Z order: When the taskbar
is created do_show_systray() is called and the taskbar is pushed to the top of
the window stack. This happens at the start of the virutal desktop, so there is
no other window at that time. When the app creates its window, it's put to the
top of the windows stack, so above the taskbar. When it is a fullscreen window,
the taskbar is hidden (in fact, any window will cover the taskbar, just move or
maximize a window over the taskbar and you'll see). So far so well.
Then, when the resolution changes, WM_DISPLAYCHANGE calls do_show_systray() and
the taskbar is pushed on top again. Since the window app is already open, it is
no more above the taskbar and the issue happens.

So, the fix is to NOT push the taskbar to the top of the z order in any case.
There is no drawback because the taskbar has never stuck 'above all windows'
anyway.

And it also fix another potential issue: When an icon is added to the systray,
show_icon() calls do_show_systray(). If it happens while a fullscreen window is
open, it will push the taskbar on top of it too and cause the issue.

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