Every Delphi project contains a global variable Screen, that is automatically created,
and that is of the type TScreen (search in the Help files for "TScreen").
To get the resolution, use Screen.Width and Screen.Height. These are the resolution
settings of the monitor of a single-monitor system, or of the "primary" monitor of a
If you foresee that some users may have multi-monitor systems, look up the Help info
on Screen.MonitorCount, Screen.Monitors (Screen.Monitors is the primary monitor, Screen.Monitors
is the second one, and so on...), TScreen.DesktopWidth, TScreen.DesktopHeight and more.