WA_TranslucentBackground doesn't work for native child widget on Windows

// Windows with alpha: Use blend function to update. 
QRect r = QHighDpi::toNativePixels(window->frameGeometry(), window); 
QPoint frameOffset(QHighDpi::toNativePixels(QPoint(window->frameMargins().left(), window->frameMargins().top()), 
                                            static_cast<const QWindow *>(nullptr))); 
QRect dirtyRect = br.translated(offset + frameOffset); 
 
SIZE size = {r.width(), r.height()}; 
POINT ptDst = {r.x(), r.y()}; 
POINT ptSrc = {0, 0}; 
BLENDFUNCTION blend = {AC_SRC_OVER, 0, BYTE(qRound(255.0 * rw->opacity())), AC_SRC_ALPHA}; 
RECT dirty = {dirtyRect.x(), dirtyRect.y(), 
              dirtyRect.x() + dirtyRect.width(), dirtyRect.y() + dirtyRect.height()}; 
UPDATELAYEREDWINDOWINFO info = {sizeof(info), nullptr, &ptDst, &size, 
                                m_image->hdc(), &ptSrc, 0, &blend, ULW_ALPHA, &dirty}; 
const BOOL result = UpdateLayeredWindowIndirect(rw->handle(), &info);