[Bug 59653] New: winex11.drv: FocusOut sends WM_CANCELMODE during active mouse grab, breaking drag operations

[WineHQ Bugzilla]

http://bugs.winehq.org/show_bug.cgi?id=59653

            Bug ID: 59653
           Summary: winex11.drv: FocusOut sends WM_CANCELMODE during
                    active mouse grab, breaking drag operations
           Product: Wine
           Version: 11.6
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: winex11.drv
          Assignee: [e-mail]
          Reporter: [e-mail]
      Distribution: ---

When a Wine application performs a drag operation (which involves an active
mouse capture via SetCapture), and the user switches focus with Alt+Tab,
XWayland sends a FocusOut event to the Wine window.

Currently, Wine's focus_out() handler in dlls/winex11.drv/event.c
unconditionally sends a WM_CANCELMODE message to the window losing focus. This
forces any well-behaved Win32 application to call ReleaseCapture() and abort
the modal drag operation.

This behavior is incorrect. On native Windows, an active mouse capture survives
keyboard focus changes. WM_CANCELMODE should not be sent in this state.

This issue is specific to the winex11.drv backend and is prominently observed
on XWayland. The native winewayland.drv does not suffer from this issue, as it
handles input grabs differently. The successful drag-and-drop in native Wayland
mode (with the ole32 fix applied) further proves that this is an X11-specific
event handling bug.


Steps to Reproduce:
    Implement patch from bug #59652 to enable drag and drop.
    Run Wine under an XWayland session.
    Start two applications (e.g., a file manager and a text editor).
    In the source application, begin a drag operation by holding the left mouse
button.
    While still holding the mouse button, press Alt+Tab to switch focus to the
other application.

Actual Results: The drag operation is silently cancelled.

Expected Results: The drag operation should continue, allowing the user to
complete the drop in the other window.

Patch: The following patch modifies focus_out() to check for an active mouse
grab (grab_hwnd) before sending WM_CANCELMODE. This aligns Wine's behavior with
native Windows and fixes the bug.

diff

--- a/dlls/winex11.drv/event.c
+++ b/dlls/winex11.drv/event.c
@@ -2019,7 +2019,15 @@
     set_focus( thread_data, NULL, NULL );

     if (!(NtUserGetWindowLongW( hwnd, GWL_STYLE ) & WS_MINIMIZE))
-        send_message( hwnd, WM_CANCELMODE, 0, 0 );
+    {
+        if (x11drv_thread_data()->grab_hwnd)
+        {
+            TRACE("Skipping WM_CANCELMODE, mouse is grabbed by %p.\\n",
x11drv_thread_data()->grab_hwnd);
+        }
+        else
+            send_message( hwnd, WM_CANCELMODE, 0, 0 );
+    }

     if (X11DRV_GetKeyboardLayout(0) != get_thread_input_hkl(0))
         X11DRV_ActivateKeyboardLayout( get_thread_input_hkl(0), 0 );

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