Determining whether game mode is active

Question

Is there an API for determining whether the user is currently playing a game, or running another graphics accelerated application in fullscreen?

Answer 1

A way is with IDirectDraw7
(tested on Windows 10 1909 (in a Timer for the test) with various games in Full Screen) =>

BOOL bRet = FALSE;
IDirectDraw7 *pDD7;
if (SUCCEEDED(CoCreateInstance(CLSID_DirectDraw7, NULL, CLSCTX_INPROC_SERVER, IID_PPV_ARG(IDirectDraw7, &pDD7))))
{
    if (S_OK == pDD7->Initialize(NULL))
    {
        bRet = pDD7->TestCooperativeLevel() == DDERR_EXCLUSIVEMODEALREADYSET;
        pDD7->Release();
    }
}
if (bRet)
{
        // Full Screen game is running
}