2,787 questions
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
}