1 files changed, 66 insertions, 0 deletions
diff --git a/wx+/focus.h b/wx+/focus.h
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--- /dev/null
+++ b/wx+/focus.h
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+// *****************************************************************************
+// * This file is part of the FreeFileSync project. It is distributed under    *
+// * GNU General Public License: https://www.gnu.org/licenses/gpl-3.0          *
+// * Copyright (C) Zenju (zenju AT freefilesync DOT org) - All Rights Reserved *
+// *****************************************************************************
+
+#ifndef FOCUS_1084731021985757843
+#define FOCUS_1084731021985757843
+
+#include <wx/toplevel.h>
+
+
+namespace zen
+{
+//pretty much the same like "bool wxWindowBase::IsDescendant(wxWindowBase* child) const" but without the obvious misnomer
+inline
+bool isComponentOf(const wxWindow* child, const wxWindow* top)
+{
+    for (const wxWindow* wnd = child; wnd != nullptr; wnd = wnd->GetParent())
+        if (wnd == top)
+            return true;
+    return false;
+}
+
+
+inline
+wxTopLevelWindow* getTopLevelWindow(wxWindow* child)
+{
+    for (wxWindow* wnd = child; wnd != nullptr; wnd = wnd->GetParent())
+        if (auto tlw = dynamic_cast<wxTopLevelWindow*>(wnd)) //why does wxWidgets use wxWindows::IsTopLevel() ??
+            return tlw;
+    return nullptr;
+}
+
+
+/*
+Preserving input focus has to be more clever than:
+    wxWindow* oldFocus = wxWindow::FindFocus();
+    ZEN_ON_SCOPE_EXIT(if (oldFocus) oldFocus->SetFocus());
+
+=> wxWindow::SetFocus() internally calls Win32 ::SetFocus, which calls ::SetActiveWindow, which - lord knows why - changes the foreground window to the focus window
+    even if the user is currently busy using a different app! More curiosity: this foreground focus stealing happens only during the *first* SetFocus() after app start!
+    It also can be avoided by changing focus back and forth with some other app after start => wxWidgets bug or Win32 feature???
+*/
+struct FocusPreserver
+{
+    ~FocusPreserver()
+    {
+        //wxTopLevelWindow::IsActive() does NOT call Win32 ::GetActiveWindow()!
+        //Instead it checks if ::GetFocus() is set somewhere inside the top level
+        //Note: Both Win32 active and focus windows are *thread-local* values, while foreground window is global! https://blogs.msdn.microsoft.com/oldnewthing/20131016-00/?p=2913
+        if (oldFocus_)
+            if (wxTopLevelWindow* topWin = getTopLevelWindow(oldFocus_))
+                if (topWin->IsActive()) //Linux/macOS: already behaves just like ::GetForegroundWindow() on Windows!
+                    oldFocus_->SetFocus();
+    }
+
+    wxWindow* getFocus()        const { return oldFocus_; }
+    void      setFocus(wxWindow* win) { oldFocus_ = win; }
+
+private:
+    wxWindow* oldFocus_ = wxWindow::FindFocus();
+};
+}
+
+#endif //FOCUS_1084731021985757843