1	SUB SMG_CLEAR(LONG Entity,LONG Portion,LONG Vir_disp_num)

	!---------------------------------------------------------------&
	!								&
	!		   	   SMG_CLEAR				&
	!								&
	!		Creation Date:  3-July-1985			&
	!		Author:		Ken Messer			&
	! 		Purpose:        Clear all or a portion of a	&
	!				virtual display			&
	!								&
	!		Modification history				&
	!								&
	!	Date	Description of change(s)			&
	!								&
	!---------------------------------------------------------------&
	!								&
	! Copyright (c) 1985 -	Ken Messer, Allied Electronics, Inc.,	&
	!			401 E. 8th St., Ft. Worth, TX  76102	&
	!								&
	! This software may be copied and distributed freely to anyone	&
	! for non-commerical use provided that this copyright notice is &
	! included.							&
	!---------------------------------------------------------------&

	OPTION TYPE = INTEGER, SIZE = INTEGER LONG

	%include "SMG$LIBRARY:SMG.DFN"


	DECLARE LONG				Return_status,		&
						Cur_row,		&
						Cur_col

	EXTERNAL LONG CONSTANT			SS$_Normal

	EXTERNAL LONG FUNCTION			SMG$Erase_line,		&
						SMG$Erase_display,	&
						SMG$Return_cursor_pos

	EXTERNAL STRING FUNCTION	Get_Error_Message(LONG)

	!---------------------------------------------------------------&
	!								&
	!		M a i n   P r o g r a m   L o g i c		&
	!								&
	!---------------------------------------------------------------&

	! Find the current cursor position so we know where we are

	Return_status = SMG$Return_cursor_pos(Display_id(Vir_disp_num),	&
		Cur_row,Cur_col)

	! Check for error

	IF Return_status AND SS$_Normal = 0   THEN
		PRINT Get_Error_Message(Return_status)
		STOP
	END IF

	! Now see what the user wants to do

	SELECT Entity

	   CASE 0	! clear the screen

		SELECT Portion

		   CASE 0	! cursor to end of screen

			Return_status = SMG$Erase_display(Display_id(Vir_disp_num), &
				Cur_row,Cur_col,,)

		   CASE 1	! cursor to beginning of screen

			Return_status = SMG$Erase_display(Display_id(Vir_disp_num), &
				1,1,Cur_row,Cur_col)

		   CASE 2	! entire screen

			Return_status = SMG$Erase_display(Display_id(Vir_disp_num),,,,)

		   CASE ELSE

			GOTO Done

		END SELECT

	   CASE 1	! clear the line

		SELECT portion

		   CASE 0	! cursor to end of line

			Return_status = SMG$Erase_line(Display_id(Vir_disp_num),,)

		   CASE 1	! cursor to beginning of line

			Return_status = SMG$Erase_display(Display_id(Vir_disp_num), &
				Cur_row,1,Cur_row,Cur_col)

		   CASE 2	! entire line

			Return_status = SMG$Erase_line(Display_id(Vir_disp_num),Cur_row,1)

		   CASE ELSE

			GOTO Done

		END SELECT

	END SELECT

	! Check for error

	IF Return_status AND SS$_Normal = 0   THEN
		PRINT Get_Error_Message(Return_status)
		STOP
	END IF

 Done:

	SUBEXIT

	END SUB