如何使窗口出现在所有内容(甚至是全屏游戏！）之上(甚至是全屏游戏！）c ++ / Qt

我正在尝试使应用程序在屏幕中心显示十字准线并保持在其他所有内容之上。目的是在一些不提供十字准线的 FPS 游戏中有一个十字准线。我已经成功地让我的窗户最上面放了除了游戏之外的一切：/

这是我的代码：（一切都是主要的，因为我只测试我的应用程序的核心功能，我已经广泛评论了它，试图让我的问题更容易理解）

QApplication app(argc, argv);
DWORD error;
QWidget window;
QLabel *label = new QLabel(&window);
label->setText("<strong>O<strong>");//I'm using an "O" as a crosshair until I can figure out how to display image transparency.
window.setGeometry(960-label->width()/2,540-label->height()/2,label->width(),label->height());//here I'm making my window appear in the center of my screen
window.setWindowFlags(Qt::FramelessWindowHint | Qt::WindowStaysOnTopHint);// here making the window frameless and topMost via qt
window.setAttribute(Qt::WA_TranslucentBackground);//making the window see through
window.setWindowTitle("Crosshair");
window.show();
//in this next part I tried using windows api to make my window appear on top of the game.
HWND handle, myHandle;
myHandle = FindWindow(NULL,TEXT("Crosshair"));//retieving my own application window handle
if(myHandle == 0){cout << "no own handle" << endl;}//it successfully retrieves it
handle = FindWindow(NULL,TEXT("Killing Floor"));//retrieving a game window handle
if(handle == 0){cout << "no KF handle" << endl;}//it successfully retrieves it
if(handle != 0 && myHandle != 0)
{
    if(SetWindowPos(handle,myHandle,0,0,0,0,SWP_NOSIZE | SWP_NOMOVE) == 0){cout << "couldnt set notopmost" << endl;}//here SetWindowPos returns 0 (function failed)
}
          // I've also tried using SetWindowPos to set the game to Not TOPMOST, it didnt work either.
          // here was my code : SetWindowPos(handle, HWND_NOTOPMOST, 0, 0, 0, 0, SWP_NOSIZE | SWP_NOMOVE);
error = GetLastError();// i tried using GetLastError to understand what was happening
cout << error << endl;// but it only returns "5", I've read that you can look in WINNT.H for information about the meanings of error codes
                      // however its a pretty big file and I wasn't able to understand where the relevant part was.

return app.exec();

我的猜测是，游戏等应用程序对显示设备有更直接的控制。我正在寻找这个问题的任何解决方案（不一定涉及透明最顶层窗口）。另外，如果有人可以向我解释如何有效地使用GetLastError（），以及为什么游戏的行为与普通窗口不同。

提前谢谢。