Category : Files from Magazines
Archive   : PWRGRPHC.ZIP
Filename : CHAP09.1

; Program to put up a mode 10h EGA graphics screen, then save it
; to the file SNAPSHOT.SCR.
;
; Updated 6/29/89.
;
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
;
stackseg segment para stack 'STACK'
db 512 dup (?)
stackseg 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
jc WriteError ;handle write error, if any
cmp ax,DISPLAYED_SCREEN_SIZE ;did all bytes get written?
jz SaveLoopBottom ;yes, no error
WriteError: ;a error occurred while writing
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