L29-1.ASM

; Program to put up a mode 10h EGA graphics screen, then save it
; to the file SNAPSHOT.SCR.
;
VGA_SEGMENT	equ   0a000h
GC_INDEX	equ   3ceh		;Graphics Controller Index register
READ_MAP	equ   4			;Read Map register index in GC
DISPLAYED_SCREEN_SIZE equ (640/8)*350	;# of displayed bytes per plane in a
					; hi-res graphics screen
;
stack	segment para stack 'STACK'
	db	512 dup (?)
stack	ends
;
Data	segment word 'DATA'
SampleText	db	'This is bit-mapped text, drawn in hi-res '
		db	'EGA graphics mode 10h.', 0dh, 0ah, 0ah
		db	'Saving the screen (including this text)...'
		db	0dh, 0ah, '$'
Filename	db	'SNAPSHOT.SCR',0;name of file we're saving to
ErrMsg1		db	"*** Couldn't open SNAPSHOT.SCR ***",0dh,0ah,'$'
ErrMsg2		db	'*** Error writing to SNAPSHOT.SCR ***',0dh,0ah,'$'
WaitKeyMsg	db	0dh, 0ah, 'Done. Press any key to end...',0dh,0ah,'$'
Handle		dw	?		;handle of file we're saving to
Plane		db	?		;plane being read
Data	ends
;
Code	segment
	assume	cs:Code, ds:Data
Start	proc	near
	mov	ax,Data
	mov	ds,ax
;
; Go to hi-res graphics mode.
;
	mov	ax,10h			;AH = 0 means mode set, AL = 10h selects
					; hi-res graphics mode
	int	10h			;BIOS video interrupt
;
; Put up some text, so the screen isn't empty.
;
	mov	ah,9			;DOS print string function
	mov	dx,offset SampleText
	int	21h
;
; Delete SNAPSHOT.SCR if it exists.
;
	mov	ah,41h			;DOS unlink file function
	mov	dx,offset Filename
	int	21h
;
; Create the file SNAPSHOT.SCR.
;
	mov	ah,3ch			;DOS create file function
	mov	dx,offset Filename
	sub	cx,cx			;make it a normal file
	int	21h
	mov	[Handle],ax		;save the handle
	jnc	SaveTheScreen		;we're ready to save if no error
	mov	ah,9			;DOS print string function
	mov	dx,offset ErrMsg1
	int	21h			;notify of the error
	jmp	short Done		;and done
;
; Loop through the 4 planes, making each readable in turn and
; writing it to disk. Note that all 4 planes are readable at
; A000:0000; the Read Map register selects which plane is readable
; at any one time.
;
SaveTheScreen:
	mov	[Plane],0		;start with plane 0
SaveLoop:
	mov	dx,GC_INDEX
	mov	al,READ_MAP	;set GC Index to Read Map register
	out	dx,al
	inc	dx
	mov	al,[Plane]		;get the # of the plane we want
					; to save
	out	dx,al			;set to read from the desired plane
	mov	ah,40h			;DOS write to file function
	mov	bx,[Handle]
	mov	cx,DISPLAYED_SCREEN_SIZE;# of bytes to save
	sub	dx,dx			;write all displayed bytes at A000:0000
	push	ds
	mov	si,VGA_SEGMENT
	mov	ds,si
	int	21h			;write the displayed portion of this plane
	pop	ds
	cmp	ax,DISPLAYED_SCREEN_SIZE;did all bytes get written?
	jz	SaveLoopBottom
	mov	ah,9			;DOS print string function
	mov	dx,offset ErrMsg2
	int	21h			;notify about the error
	jmp	short DoClose		;and done
SaveLoopBottom:
	mov	al,[Plane]
	inc	ax			;point to the next plane
	mov	[Plane],al
	cmp	al,3			;have we done all planes?
	jbe	SaveLoop		;no, so do the next plane
;
; Close SNAPSHOT.SCR.
;
DoClose:
	mov	ah,3eh			;DOS close file function
	mov	bx,[Handle]
	int	21h
;
; Wait for a keypress.
;
	mov	ah,9			;DOS print string function
	mov	dx,offset WaitKeyMsg
	int	21h			;prompt
	mov	ah,8			;DOS input without echo function
	int	21h
;
; Restore text mode.
;
	mov	ax,3
	int	10h
;
; Done.
;
Done:
	mov	ah,4ch			;DOS terminate function
	int	21h
Start	endp
Code	ends
	end	Start