[Bug 52811] New: Apps starting with wrong non-client area decoration

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=52811

Bug ID: 52811
           Summary: Apps starting with wrong non-client area decoration
           Product: Wine
           Version: 7.6
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: trivial
          Priority: P2
         Component: user32
          Assignee: [e-mail]
          Reporter: [e-mail]
      Distribution: ---

Created attachment 72186
  --> https://bugs.winehq.org/attachment.cgi?id=72186
Small client to reproduce the bug

Arch Linux
wine-6.0-rc1-11894-gafd7b319e56

---

# Bug description

During the development of the Wine Wayland driver we've noticed a bug that also
affects the X11 driver when using client-side decorations.

Some applications start with the wrong decoration. It's a visual-only issue, as
the application starts with focus and works nicely. But its non-client area
starts with the decoration of inactive applications (greyed out).

This is how it should start:
https://share.collabora.com/index.php/s/tZQxBEaybgwGgpi

But this is how it looks like:
https://share.collabora.com/index.php/s/bQbASjTXg8oxg3W

---

# How to reproduce

You can easily reproduce this by running notepad with the X11 driver option
"Decorated" set to "N". I wrote some small clients to debug this, and the
simple program attached reproduces the issue. TLDR: it is a program that
activates a window of a non-foreground thread and then tries to show it.

---

# What I think is going on

When we call SetActiveWindow(hwnd), hwnd does not become the foreground window,
as the application thread is not the foreground thread yet (at this point the
desktop window is the foreground window). SetActiveWindow() activates the
non-client area only if the window is the foreground window, so we have
activated the window but didn't activate its non-client area (which is correct
AFAIU).

Next we call ShowWindow(hwnd), and now the thread that owns hwnd should become
foreground and SetActiveWindow(hwnd) is called. But as hwnd is already active
it does nothing and returns, so the non-client area is draw as inactive.

---

# Possible fix

In order to fix this, we could change SetActiveWindow() behavior to the
following:

if (hwnd == current active window)
       if (hwnd == NtUserGetForegroundWindow() && non-client area of hwnd not
active)
           activate non-client area of hwnd
       bail out

I wrote a test for this, and I could see that this fix didn't break any other
tests. I've decided to post here in order to know if the fix seems reasonable
to you.

Also, I had a question while debugging this and still couldn't figure out. I
thought that focus was a global property related to the foreground window. But
it seems that when a window is set to active the function to change the focus
to it may also be called (even when the window does not belong to the
foreground thread). So can a non-foreground window be active and have the
focus?

---

Thanks a lot!