Have you ever wanted to draw or write something on top of another window using GDI? It can be done by obtainig a DC to the desktop window and then using normal drawing functions on it. For example:
HDC hDC;
hDC = CreateDC("DISPLAY", NULL, NULL, NULL);
if (hDC) {
TextOut(hDC, 0, 0, "Hello world!", 12);
DeleteDC(hDC);
}
This will write 'Hello world!' in the upper left corner of your screen.