CustomFrame: Allow to specify a callback for QWindow opt-in

Which QWindows should get a custom frame is up to you. Just
return true in the callback.

src/private/WidgetResizeHandler.cpp

@@ -561,9 +561,10 @@ bool NCHITTESTEventFilter::nativeEventFilter(const QByteArray &eventType, void *
 #endif
 
 
-CustomFrameHelper::CustomFrameHelper(QObject *parent)
+CustomFrameHelper::CustomFrameHelper(ShouldUseCustomFrame func, QObject *parent)
     : QObject(parent)
     , QAbstractNativeEventFilter()
+    , m_shouldUseCustomFrameFunc(func)
 {
 #ifdef Q_OS_WIN
     qApp->installNativeEventFilter(this);
@@ -588,6 +589,9 @@ void CustomFrameHelper::applyCustomFrame(QWindow *window)
 bool CustomFrameHelper::nativeEventFilter(const QByteArray &eventType, void *message,
                                           Qt5Qt6Compat::qintptr *result)
 {
+    if (m_shouldUseCustomFrameFunc == nullptr)
+        return false;
+
 #ifdef Q_OS_WIN
     if (m_inDtor || !KDDockWidgets::usesAeroSnapWithCustomDecos())
         return false;
@@ -598,7 +602,7 @@ bool CustomFrameHelper::nativeEventFilter(const QByteArray &eventType, void *mes
     auto msg = static_cast<MSG *>(message);
 
     QWindow *window = QWindow::fromWinId(WId(msg->hwnd));
-    if (!window)
+    if (!window || !m_shouldUseCustomFrameFunc(window))
         return false;
 
     const char *propertyName = "kddw_customframe_setup_ran";

src/private/WidgetResizeHandler_p.h

@@ -124,13 +124,16 @@ public:
 
 #endif // Q_OS_WIN
 
+typedef bool (*ShouldUseCustomFrame)(QWindow *);
+
 class DOCKS_EXPORT CustomFrameHelper
     : public QObject
     , public QAbstractNativeEventFilter
 {
     Q_OBJECT
 public:
-    explicit CustomFrameHelper(QObject *parent = nullptr);
+    explicit CustomFrameHelper(ShouldUseCustomFrame shouldUseCustomFrameFunc,
+                               QObject *parent = nullptr);
     ~CustomFrameHelper() override;
 
 public Q_SLOTS:
@@ -142,6 +145,7 @@ protected:
 
 private:
     bool m_inDtor = false;
+    ShouldUseCustomFrame m_shouldUseCustomFrameFunc = nullptr;
 };
 }