dropsy source code

;DROPSY TEXT effect for Nowhere Man's VCL - TASM will assemble as is using
;VCL recommended switches. When screen is thoroughly dropsie'd, that is all
;letters have fallen to a single line across the bottom of the monitor,
;the routine will exit to DOS and restore the command prompt. I excerpted
;quite a bit of this from some public domain video routines optimized for
;the accursed a86 assembler and reworked the whole magilla until TASM
;wouldn't choke when swallowing the source. It attempts to meet
;minimum requirements for VCL formatting. Heck, this is a nice routine
;to have at your fingertips; you gotta admit a CASCADE-virus-like effect
;is always something people wanna see. And it's commented up the
;kazoo, one of the features I like best about VCL code. Hope you find
;it useful. -URNST KOUCH

code segment byte public
assume cs:code,ds:code,es:code,ss:code
org 0100h

jmp Start

main proc near

Row dw 24 ;Rows to do initially

;First, get current video mode and page.
Start: mov cx,0B800h ;color display, color video mem for page 1
mov ah,15 ;Get current video mode
int 10h
cmp al,2 ;Color?
je A2 ;Yes
cmp al,3 ;Color?
je A2 ;Yes
cmp al,7 ;Mono?
je A1 ;Yes
int 20h ;No,quit

;here if 80 col text mode; put video segment in ds.
A1: mov cx,0A300h ;Set for mono; mono videomem for page 1
A2: mov bl,0 ;bx=page offset
add cx,bx ;Video segment
mov ds,cx ;in ds

;start dropsy effect
xor bx,bx ;Start at top left corner
A3: push bx ;Save row start on stack
mov bp,80 ;Reset column counter
;Do next column in a row.
A4: mov si,bx ;Set row top in si
mov ax,[si] ;Get char & attr from screen
cmp al,20h ;Is it a blank?
je A7 ;Yes, skip it
mov dx,ax ;No, save it in dx
mov al,20h ;Make it a space
mov [si],ax ;and put on screen
add si,160 ;Set for next row
mov di,cs:Row ;Get rows remaining
A5: mov ax,[si] ;Get the char & attr from screen
mov [si],dx ;Put top row char & attr there
A6: call Vert ;Wait for 2 vert retraces
mov [si],ax ;Put original char & attr back
;Do next row, this column.
add si,160 ;Next row
dec di ;Done all rows remaining?
jne A5 ;No, do next one
mov [si-160],dx ;Put char & attr on line 25 as junk
;Do next column on this row.
A7: add bx,2 ;Next column, same row
dec bp ;Dec column counter; done?
jne A4 ;No, do this column
;Do next row.
A8: pop bx ;Get current row start
add bx,160 ;Next row
dec cs:Row ;All rows done?
jne A3 ;No
A9: mov ax,4C00h
int 21h ;Yes, quit to DOS with error code

;routine to deal with snow on CGA screen.
Vert: push ax
push dx
push cx ;Save all registers used
mov cl,2 ;Wait for 2 vert retraces
mov dx,3DAh ;CRT status port
F1: in al,dx ;Read status
test al,8 ;Vert retrace went hi?
je F1 ;No, wait for it
dec cl ;2nd one?
je F3 ;Yes, write during blanking time
F2: in al,dx ;No, get status
test al,8 ;Vert retrace went low?
jne F2 ;No, wait for it
jmp F1 ;Yes, wait for next hi
F3: pop cx
pop dx
pop ax ;Restore registers
ret ;and return

main endp
code ends
end main