How to make a window appear on top of everything (even full screen games!) c++/Qt

Question

I'm trying to make an application displaying a crosshair at the center of the screen and staying on top of everything else. The aim is to have a crosshair in some FPS games that doesn't provide one. I've succesfully made my window topmost for everything except the games :/

Here is my code : (everything is in the main since im only testing the core functionalitys of my app, I've commented it extensively to try and make my problem more accessible)

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();

My guess is that application such as games have a more direct control over the display device. I'm looking for any solution to this problem (not neccesseraly one involving a transparent topmost window). Also on a sidenote if someone could explain to me how to effectively use GetLastError(), and also why are game behaving differently than a common window.

Thanks in advance.

Answer 1

I know this doesn't really help you, but please have a look at this post from Raymond Chen: How do I create a topmost window that is never covered by other topmost windows?

Answer 2

From the SetWindowPos() documentation:

A window can be made a topmost window either by setting the hWndInsertAfter parameter to HWND_TOPMOST and ensuring that the SWP_NOZORDER flag is not set, or by setting a window's position in the Z order so that it is above any existing topmost windows. When a non-topmost window is made topmost, its owned windows are also made topmost. Its owners, however, are not changed.

Also from the same page:

To use SetWindowPos to bring a window to the top, the process that owns the window must have SetForegroundWindow permission.

However, I guess the link is for Windows Vista and above.