Assembly
Shows a demonstration of a routine which scrolls a window on a text mode screen
Shows a demonstration of a routine which scrolls a window on a text mode screen %SUBTTL "Scroll Window Left routine with sample driver" ; ; Scroll2.Asm ; ; see ScrollLeft description for complete explanation of this program ; MODEL small IDEAL STACK 200h ; this is more than enough stack CODESEG start: ; ; this test stub scrolls the window at (4,3)-(22,68) left 9 columns, ; filling in with spaces of attribute white on black (07) ; mov al,9 ; number of columns to scroll mov bh,07 ; attribute to use for blanked chars mov ch,4 ; row of upper left hand corner of window mov cl,3 ; col of upper left hand corner of window mov dh,22 ; row of lower right hand corner of window mov dl,68 ; col of lower right hand corner of window call ScrollLeft mov ah,4ch ; exit with errorlevel from scroll routine int 21h ; ; ScrollLeft ; ; PURPOSE: scrolls a rectangular region of a text screen (window) to the ; left by a variable number of columns ; ; ; INPUTS: AL = number of columns to scroll (if zero, no effect) ; BH = attribute to use for blanked characters ; CH,CL = row, col for upper left hand corner of window ; DH,DL = row, col for lower right hand corner of window ; ; NOTES: upper left hand corner of screen (home) is (0,0) ; video adapter is checked to see if it's in text mode ; screen dimensions are taken from BIOS data ; calling sequence is nearly identical to BIOS scroll routine ; display pages supported ; dual monitors supported ; MDA/CGA/EGA/VGA supported ; ; RETURNS: On error, Carry flag set, AX contains error number ; otherwise carry is clear, AX contains 0 ; ; Error codes: 0 - no error ; -1 - some error occurred ; PROC ScrollLeft ScrRows equ 0484h ; location of BIOS rows data ScrCols equ 044ah ; location of BIOS cols data ScrMode equ 0449h ; location of BIOS mode data ScrOffs equ 044eh ; location of BIOS scrn offset data ; first, save all of the registers we're going to trash push bx push cx push dx push si push di push bp push es push ds mov bl,al ; stow cols in BL xor ax,ax mov ds,ax ; point data seg to 0000 to read BIOS data cmp ch,dh ; srow > erow ? ja @@badcoords cmp cl,dl ; scol > ecol ? ja @@badcoords ; ; now we need to load ScrRows, if we haven't got EGA or better ; mov al,[ScrRows] ; is MAXROWS = 0 ? cmp al,0 ; if so, then assume we've got MDA or CGA jne @@ega_plus ; if not, we've got correct value already mov al,24 ; otherwise, assume 25 rows (and load 25-1) @@ega_plus: cmp dh,al ; erow >= MAXROWS? ; ; note that BIOS actually stores MAXROWS-1 in this location, so the ; actual jump instruction is (correctly) written as ja ; ja @@badcoords cmp dl,[ScrCols] ; ecol >= MAXCOLS? jae @@badcoords mov ah,bl ; remember cols add ah,cl ; cols + scol cmp ah,dl ; (cols + scol) > ecol ? ja @@badcoords ; figure out where the video buffer starts mov bp,0b800h ; first guess mov al,[ScrMode] ; get mode from BIOS' RAM cmp al,4 ; if mode is 0 through 3, we're all set jb @@modeOK mov bp,0b000h ; second guess cmp al,7 ; is it mode 7 (monochrome 80 col) ? je @@modeOK ; if so, we're still OK @@badcoords: mov ax,-1 ; set error code stc ; and set error (carry) flag jmp @@exit @@modeOK: mov es,bp ; set up our video pointer segment ; ES:DI = endloc = Screen + 2 * (MAXCOLS * srow + scol) mov di,[ScrOffs] ; offset of screen buffer xor ah,ah ; clear out high half of AX mov al,[ScrCols] ; get the width of the screen mul ch ; multiply width by the row number add al,cl ; now add the column number adc ah,0 ; propagate carry bit to other half of AX shl ax,1 ; now multiply by 2 bytes/char add di,ax ; add the offset to the screen start address ; DS:DI = startloc = endloc + 2 * cols xor ah,ah ; clear top half of ax mov al,bl ; recall cols mov si,di ; start address = end address add si,ax ; add cols add si,ax ; and again ; start on count calculation (figure ecol-scol+1) sub dl,cl ; ecol - scol inc dl ; now dl = ecol - scol + 1 ; calculate increment and stow in BP ; increment = (MAXCOLS - (ecol - scol + 1)) * 2 xor ah,ah ; clear top half of ax mov al,dl ; use partial count calculation neg ax add al,[ScrCols] ; now add in screen width adc ah,0 ; propagate carry bit to hi half of AX shl ax,1 ; now double it (2 bytes/char) mov bp,ax ; finish count calculations and put in DL ; count = (ecol - scol + 1) - cols sub dl,bl ; figure in cols mov ax,es ; recall our video pointer mov ds,ax ; now duplicate it ; load up AX with char and attribute for blank space mov al,32 ; ASCII space character mov ah,bh ; passed attribute byte sub dh,ch ; get row count mov dh,bh ; save loop count (rows to move) in bh xor ch,ch ; zero out hi half of CX cld ; assure that we move the right direction (up) @@looptop: mov cl,dl ; load in count (words to move) rep movsw ; move the line over mov cl,bl ; recall cols (blanks to insert) rep stosw ; fill in the rest of the line add di,bp ; advance to next line by adding increment mov si,di ; now set up the other (source) pointer mov cl,bl ; recall cols add si,cx ; add in cols add si,cx ; and again (because 2 bytes/char) dec bh ; decrement loop counter ja @@looptop ; skip back if we're not done yet mov ax,0 ; set error code to zero (all OK) clc ; and clear error (carry) flag @@exit: pop ds ; restore all of our registers pop es pop bp pop di pop si pop dx pop cx pop bx ret ; mosey on home again ENDP ScrollLeft END start -+------- cut here -----------
Shows a demonstration of a routine which scrolls a window on a text mode screen
