;===========================================================================
;
;    S C R N B L T  -  Graphics Screen Block Transfer for Turbo Pascal
;
;===========================================================================
;
;     by Larry Stone      21-Jul-84
;
; SCRNBLT is written to be called from Turbo Pascal V2.0 using the
; EXTERNAL procedure convention.  It will copy the contents of the
; video graphics display buffer (either low or high resolution) to
; a designated memory location on a virtual "pad" of set dimensions.
; 
; To use SCRNBLT, the following lines must be included in your Turbo
; Pascal program.  The type "padtype" demonstrates how a PAD data type
; may be declared. When the PAD type is declared, the dimensions of
; the array must be as shown here.  It should also be specified ABSOLUTE
; with the initial offset 0, so that all of a 64K segment is available
; to it.
;
;  PROCEDURE SCRNBLT( MOVDIR, PADX, PADY : INTEGER; VAR PAD : PADARRAY );
;	  EXTERN 'SCRNBLT';
;
;  TYPE
;	padtype = ARRAY [0..159, 0..399] OF BYTE;
;  VAR
;       pad : padtype ABSOLUTE $BA00 : $0000;    (* sample declaration *)
;
;  SCRNBLT(0, x, y, pad);   (* sample call; saves screen on pad(x,y) *)
;
; The parameters PADX and PAXY are specified as absolute coordinates
; on the pad, exactly as screen coordinates would be specified.  The
; X-coordinates correspond to the bits on the pad, not the bytes.
;
; The first parameter, "MOVDIR", determines the direction of the transfer.
; If 0 is specified, the contents of the screen are transferred to the
; designated area of the pad; if a nonzero number is specified, 
; the designated area of the pad is transferred to the screen buffer.
;
; SCRNBLT transfers the contents of the screen as a rectangular block,
; 80 bytes wide by 200 bytes high, to a rectangular area of the pad
; at the designated x,y coordinates.  The pad area is not organized
; exactly like the display buffer; odd and even lines are interleaved
; in a more straightforward fashion to allow the offset of an x,y location
; in the pad to be calculated as  (y * padwidth) + x.  
;
; To use SCRNBLT with a Turbo Program:
;-------------------------------------
; 1. Assemble this file with MASM.  "A> MASM SCRNBLT;"
; 2. Link it into a .EXE file.      "A> LINK SCRNBLT;"
; 3. Use EXE2BIN to make a .COM file. "A> EXE2BIN SCRNBLT.EXE SCRNBLT.COM"
; 4. Declare as shown in your Turbo Pascal program.
; 5. Ignore any minor diagnostic messages that may be generated when
;    this file is assembled and linked.  EXE2BIN is supplied with the
;    supplemental programs for PC-DOS; see the DOS manual.
;

; 
; EQUATES TO DEFINE GRAPHICS CONSTANTS
;
PADWD	EQU	160			; WIDTH OF VIRTUAL PAD, BYTES
SCRNWD	EQU	80			; WIDTH OF REAL SCREEN
SCRNWD2	EQU	40			; HALF OF SCREEN WIDTH
HALFSC	EQU	100			; LINES FOR HALF OF SCREEN
EVENSC	EQU	0B800H			; ADDRESS OF EVEN HALF OF SCREEN
ODDSC	EQU	02000H			; OFFSET OF ODD HALF OF SCREEN

CODE	SEGMENT PUBLIC
	ASSUME  CS:CODE
	PUBLIC  SCRNBLT
;
; EQUATES FOR ARGUMENTS TO SCRNBLT
;
PADOFS	EQU	4[BP]			; OFFSET OF PAD ORIGIN
PADSEG	EQU	6[BP]			; SEGMENT OF PAD 
PADY	EQU	8[BP]			; Y-COORD IN PAD
PADX	EQU	10[BP]			; X-COORD IN PAD
MOVDIR  EQU 	12[BP]			; MOVE DIRECTION (0 = TO SCREEN) 

SCRNBLT	PROC	NEAR
	PUSH	BP
	MOV	BP,SP			; CALLING CONVENTION
	PUSH	DS			; SAVE DS
;
; COMPUTE THE ADDRESS OF THE ORIGIN OF THE PAD AREA DESIGNATED BY
; PADX, PADY.  LOC = PAD_OFFSET + (PADY * PADWD) + (PADX / 8)
;
	MOV	AX,PADY			; PREPARE PADY * PADX
	MOV	BX,PADWD	
	MUL	BX			; AX = PADY * PADX (DX TRASHED)
	MOV	BX,PADX			; ADD IN X COMPONENT:
	MOV	CL,3			; (PREPARE TO SHIFT BY 3)
	SHR	BX,CL			;  DIV BY 8 SO WE MOVE BY BYTE
	ADD	AX,BX			;  ADD IT IN.
	ADD 	AX,PADOFS	
	CMP	WORD PTR MOVDIR,0	; IS MOVDIR 0?
	JE	BACKWRD			; IF SO, DO BACKWARDS MOVE.
;----------------------------------------------------
; MOVE "FORWARD" : FROM PAD TO REAL SCREEN
;----------------------------------------------------
;  MOVE THE EVEN LINES OF THE SCREEN. THE LOOP IS CONTROLLED BY
;  THE HALFSC VALUE IN DX; A REP MOVSW IS USED TO MOVE THE SCREEN
;  LINES A WORD AT A TIME (PROBABLY NO MORE EFFICIENT ON AN 8088..)
;
	CLD				; BE SURE DIR. FLAG IS 0
	MOV	BX,PADSEG		; SOURCE IS PAD, SO SET DS TO
	MOV	DS,BX			;  PAD SEGMENT
	MOV     SI,AX			;  AND DI TO OFFSET IN PAD
	MOV	BX,EVENSC		; DEST IS SCREEN, SET ES TO SCREEN
	MOV	ES,BX			;  SEGMENT.
	MOV	DI,0			;  AND INDEX OF 0
;
; LOOP TO COPY EVEN LINES
;
	MOV 	CX,HALFSC		; PREPARE LOOP COUNTER
EVEN:	MOV	DX,CX			; RECORD LOOP COUNTER
	MOV	CX,SCRNWD2		; SET UP COUNTER
	REP	MOVSW			; DO THE MOVE
	ADD	SI,PADWD+PADWD-SCRNWD	; MOVE SI TO NEXT SCREEN LINE
	MOV	CX,DX
	LOOP 	EVEN
;
; NOW SET UP FOR ODD LINES AND COPY THOSE
;
	MOV	DI,ODDSC		; SET DI TO ODD SCREEN OFFSET
	MOV	SI,AX
	ADD	SI,PADWD		; SET SI TO FIRST ODD LINE
;
; COPY ODD LINES
; 
	MOV	CX,HALFSC		; LOAD COUNTER
ODD:	MOV	DX,CX			; SAVE COUNTER
	MOV	CX,SCRNWD2		; SET UP LINE COUNTER
	REP	MOVSW
	ADD	SI,PADWD+PADWD-SCRNWD	; MOVE SI TO NEXT SCREEN LINE
	MOV	CX,DX			; GET LOOP COUNTER
	LOOP	ODD
	JMP	BYE			; LEAVE
;----------------------------------------------------
; MOVE "BACKWARD" : FROM REAL SCREEN TO PAD
;----------------------------------------------------
;  THIS IS ALMOST EXACTLY LIKE THE CODE ABOVE THAT MOVES
;  FROM THE VIRTUAL SCREEN TO THE DISPLAY BUFFER
;
BACKWRD:
	CLD				; BE SURE DIR. FLAG IS 0
	MOV	BX,PADSEG		; DEST IS PAD, SO SET ES TO
	MOV	ES,BX			;  PAD SEGMENT
	MOV	DI,AX			; SET UP SOURCE INDEX
	MOV	BX,EVENSC		; SET DS TO SCREEN SEGMENT
	MOV	DS,BX			;  FOR EVEN LINES OF SCREEN
	MOV	SI,0			;  AND SOURCE INDEX
;
; LOOP TO COPY EVEN LINES
;
	MOV 	CX,HALFSC		; PREPARE LOOP COUNTER
BEVEN:	MOV	DX,CX			; RECORD LOOP COUNTER
	MOV	CX,SCRNWD2		; SET UP COUNTER
	REP	MOVSW			; DO THE MOVE
	ADD	DI,PADWD+PADWD-SCRNWD	; MOVE SI TO NEXT SCREEN LINE
	MOV	CX,DX
	LOOP 	BEVEN
;
; NOW SET UP FOR ODD LINES AND COPY THOSE
;
	MOV	SI,ODDSC		; SET DI TO ODD SCREEN OFFSET
	MOV	DI,AX
	ADD	DI,PADWD		; SET SI TO FIRST ODD LINE
;
; COPY ODD LINES
; 
	MOV	CX,HALFSC		; LOAD COUNTER
BODD:	MOV	DX,CX			; SAVE COUNTER
	MOV	CX,SCRNWD2		; SET UP LINE COUNTER
	REP	MOVSW
	ADD	DI,PADWD+PADWD-SCRNWD	; MOVE SI TO NEXT SCREEN LINE
	MOV	CX,DX			; GET LOOP COUNTER
	LOOP	BODD
;
; DONE.. CLEAN UP THE STACK AND LEAVE
;
BYE:	POP	DS			; RESTORE DS
	MOV	SP,BP
	POP	BP			; CONVENTIONAL RETURN
	RET 	10			; TRASH 10 BYTES FOR PARMS

SCRNBLT	ENDP
CODE	ENDS
	END