;This program waits for user input. if the user inputs "coolprog" a triangle will be drawn. otherwise the program will print an error.
.model small
.stack 100h
.data 

p = 9                    ;maximum string support: 49 chars
startp = 0               ;x=0,y=0
line = 200               ;the length of the first line is 200 pixels

st_msg db 'Enter password: ',0dh,0ah,'> $'
in_str db p,0, 8 dup (0dh), '$'
err_msg db 'incorrect password$'
dlstr db 'coolprog'
strlen db ?

.code

       mov ax,@data
       mov ds,ax
       mov es,ax
       
       mov ax,3
       int 10h
       
init:  lea dx,st_msg      ;prints out st_msg
       mov ah,9           ;
       int 21h            ;
       
       lea dx,in_str      ;reads in in_str
       mov ah,0ah         ;
       int 21h            ;

       call chrfix
       
       mov cx,8           ;check the full length of the password 'coolprog' = 8 chars long
       lea si,in_str      ;insert in_str to si
       lea di,dlstr       ;insert dlstr to di
       rep cmpsb          ;run a comparison between the two for 8 chars, if not equal, jump to err
       jne err
       jmp done
       
err:   call newl
       lea dx,err_msg     ;prints out err_msg
       mov ah,9           ;
       int 21h            ;
       call newl
       jmp init
       
done:  mov ax,0013h       ;set vga mode
       int 10h            ;
       mov ax,0a000h      ;
       mov ds,ax          ;
       
       mov di,startp      ;set start location
       mov al,1           ;set start color
       mov bx,line
dr:    call draw          ;draw a single line
       add di,321         ;move to the start of the next line
       sub di,bx          ;
       inc al             ;increase color
       cmp al,100
       jb cont
       mov al,1
cont:  sub bx,2           ;shorten line. when reaches 0 the loop stops
       jnz dr       

mov ah,8                  ;will cause the program to hang until the user presses any key
  int 21h
mov ah,4ch                ;return control to OS
  int 21h
;*******************
draw:                     ;method that draws a line starting at startp
       mov cx,bx          ;length of line
lin:   mov [di],al        ;draw a single pixel
       inc di             ;move 1 pixel
       loop lin
   ret 
;*******************
chrfix:push cx            ;method that fixes extra chars that stick to the beginning of a string
       push si            ;register backup
       push ax            ;
       
       mov al,in_str[1]   ;find the length of the string
       mov strlen,al
       mov cl,strlen
       mov ch,0      
       mov si,2           
fix:   mov al,in_str+si   ;shift all characters 2 spaces left and fill in the remaining 2 with '0dh'
       mov in_str+si-2,al 
       inc si             
       loop fix
       sub si,2           
       mov in_str+si,0dh
       mov in_str+si+1,0dh
       
       pop ax             ;register restore
       pop si             ;
       pop cx             ;
   ret
;*******************   
newl:  mov ah,2           ;method that moves the cursor to the next line
       mov dl,10          ;drop 1 line
       int 21h            ;
       mov dl,13          ;go to start of line
       int 21h            ;
   ret    
end