[hint / solution] low framerate when window has not the focus

To avoid that, go to winWindow.cc line 958.
In Platform::process() you will find this piece of code:

HWND window = GetForegroundWindow();
   if (window && window != winState.appWindow && gWindowCreated)
   {
      // check to see if we are in the foreground or not
      // if not Sleep for a bit or until a Win32 message/input is recieved
      DWORD foregroundProcessId;
      GetWindowThreadProcessId(window, &foregroundProcessId);
      if (foregroundProcessId != winState.processId)
         MsgWaitForMultipleObjects(0, NULL, false, getBackgroundSleepTime(), QS_ALLINPUT);
   }
   // if there's no window, we sleep 1, otherwise we sleep 0
   else if(!Game->isJournalReading() && gWindowCreated )
      Sleep( 1 ); // give others some process time if necessary...

Comment out this code or simple comment out this single line

MsgWaitForMultipleObjects(0, NULL, false, getBackgroundSleepTime(), QS_ALLINPUT);

Recompile the engine. After that, you will not have any drop down of the framerate even when your window has not the focus.