Snake Assembly 8086：动作不正确

.model small
.data

;variables needed for snake body


head db '@', '$' ;head and body symbols
tail db ' ', '$' ;tail part set color to black

snake_length db 3 ; 1-2 body 3 tail
copy_snake_length db ? ;for loop
sEnd db ?

head_col db 40 ;starting col for snake 
head_row db 12 ;starting row for snake

; snake movement algorithm
; always copy the coordinates of the symbol in front.
copy_col db ?
copy_row db ?


delaytime db 1
;variable for control keys
input db ?
.stack 100h
.code

;to delay time
delay proc
    mov ah, 00
    int 1Ah
    mov bx, dx

jmp_delay:
    int 1Ah
    sub dx, bx
    cmp dl, delaytime
    jl jmp_delay
    ret

delay endp

;make snake head go to the right

righty proc
    cmp head_col,79
    je resetposl

    zero: 
    inc head_col
    jmp rightyie

    resetposl:
    mov head_col, 0


    rightyie:
    mov dl,head_col
    mov dh,head_row
    xor bh, bh

    mov ah, 02h
    int 10h
    ret 
righty endp

startgame proc

    mov dh, 12 ;row
   mov dl, 40 ;column
   xor bh, bh
   mov ah, 02h
   int 10h 

    mov dx, offset head
            mov ah, 09h
                int 21h
ret
startgame endp


mov cl, head_row
mov copy_row,cl

mov cl, head_col
mov copy_col, cl

;print head
mov dh, head_row
mov dl, head_col
xor bh, bh
mov ah, 02h
int 10h 
mov dx, offset head
mov ah, 09h
int 21h





main    proc
    mov ax, @data
    mov ds, ax

    ;set video mode
    mov al, 03h 
    mov ah, 00h
    int 10h

    ;clear screen
    ;only need it once (reason no need to use function)
    mov ax, 0600h
    mov bh, 07h
    xor cx, cx
    mov dx, 184fh
    int 10h

    mov cx, 3200h  ;stop cursor blinking
    mov ah, 01h
    int 10h

;set start head snake in the middle of the screen
    call startgame


;control
mov ah,00h
int 16h
mov input, 'd'

;to change direction or to keep on going
getinput:
mov ah, 01h
int 16h
jz key
mov ah,00h
int 16h
mov input,al

;control keys
key:
;cmp input, 'w'
;je w 
;cmp input, 's'
;je s 
;cmp input, 'a'
;je a 

cmp input, 'd'
je d

jne rak


d:

    mov cl, head_row
    mov copy_row,cl
    mov cl, head_col
    mov copy_col, cl

    mov dh, head_row
    mov dl, head_col
    xor bh, bh
    mov ah, 02h
    int 10h     

    mov al, tail
    mov bh, 0
    mov bl, 000h
    mov cx, 1
    mov ah, 09h
    int 10h

mov cl, snake_length
mov copy_snake_length, cl
dec copy_snake_length

mov bl,0

printbody:
mov al, head_row
mov copy_row,al
mov al, head_col
mov copy_col, al

call righty

;print head
;coordinates
    mov dh, head_row
    mov dl, head_col
    xor bh, bh
    mov ah, 02h
    int 10h 
;printing "@"
    mov dx, offset head
    mov ah, 09h
    int 21h

; inc copy_col to update the head.
inc copy_col
mov al,copy_col
mov head_col,al

inc bl
; now loop to print other characters
cmp bl,copy_snake_length

jl printbody
dec head_col
jmp rak






rak: 
call delay
jmp getinput


mov ax, 4c00h
int 21h
main endp
end main

如果要试用代码，请按d移动角色 .

问题是，当它到达最后一列时，我的函数正确地将head_col更改为0，使其看起来像是到达屏幕的末尾 . 不幸的是，它在结尾80处留下了一个字符，然后它继续打印但在下一行 .

然后当它到达第13行的末尾时，它不会在col 0处留下一个字符，但仍然会向下移动另一行，并且在3继续打印之后，它似乎返回到原始行，然后当它到达起始点时它不再打印任何东西了 .