Sets the system to graphics mode and clears the screen.
procedure SetGraphMode(Mode: Integer);
Mode must be a valid mode for the current device driver. SetGraphMode is used to select a graphics mode different than the default one set by InitGraph.
SetGraphMode can also be used in conjunction with RestoreCrtMode to switch back and forth between text and graphics modes.
SetGraphMode resets all graphics settings to their defaults (current pointer, palette, color, viewport, and so on).
GetModeRange returns the lowest and highest valid modes for the current driver.
If an attempt is made to select an invalid mode for the current device driver, GraphResult returns a value of grInvalidMode.
A successful call to InitGraph must have been made before calling this routine.