locals
.model tiny
.code
org 100h
.386


start:
jmp main

delay   db  1h
cur_teak    db  0h

m08_handler proc
    pusha
    mov ah, 0ch
    mov al, cur_color
    mov bh, our_page
    mov cx, 00h
    mov dx, 00h
    int 10h
    mov al, cur_teak
    cmp al, delay
    je @@move
    inc cur_teak
    jmp @@end

@@move:
    call move_snake
    mov cur_teak, 0h
@@end:
    popa
    iret
m08_handler endp

move_snake proc
    cmp direct, 0
    jne @@is_up
    sub head_x, 5
    jmp @@end
@@is_up:
    cmp direct, 1
    jne @@is_right
    sub head_y, 5
    jmp @@end

@@is_right:
    cmp direct, 2
    jne @@down
    add head_x, 5
    jmp @@end
@@down:
    add head_y, 5
@@end:
    mov di, offset map
    add di, word ptr(head_x)
    mov al, head_y
    mov bl, 64
    mul bl
    add di, ax
    mov al, 1
    stosb
    call draw_head
    ret
move_snake endp

draw_head proc
    mov al, head_x
    mov bl, 05h
    mul bl
    mov start_column, ax
    mov al, head_y
    mul bl
    mov start_line, ax

    mov ax, snake_point_size
    mov cur_point_size, ax

    mov al, snake_color
    mov cur_color, al

    call draw_point
    ret
draw_head endp


get_old_mode proc
    push    ax
    push    bx
    push    ds

    xor     ax,ax
    mov     ds, ax
    mov     bh, ds:449h

    pop     ds
    mov     [old_vm], bh
    pop     bx
    pop     ax
    ret
get_old_mode endp


get_old_page proc
    push    ax
    push    bx
    push    ds

    xor     ax,ax
    mov     ds, ax
    mov     bh, ds:462h

    pop     ds
    mov     [old_page], bh
    pop     bx
    pop     ax
    ret
get_old_page endp

change_vm proc
    push bp
    mov bp, sp
    push ax

    ; в стеке vm -> ap -> bp -> ax
    mov ah, 00h
    mov al, [bp+6] ;vm
    int 10h

    mov ah, 05h
    mov al, [bp+4] ;ap
    int 10h

    pop ax
    pop bp
    ret 4
change_vm endp

change_mode proc
    call get_old_mode
    call get_old_page

    xor ax, ax
    mov al, our_vm
    push ax
    mov al, our_page
    push ax

    call change_vm

    ret
change_mode endp

draw_point proc
    ;   устанавливаем размер клетки в cur_point_size,
    ;   цвет клетки в cur_color,
    ;   начальную позицию в start_line, start_column
    pusha; ax sp bp si di
    mov ax, cur_point_size
    mov temp_position_x, ax
    mov temp_position_y, ax

    mov ax, start_line
    mov temp_line, ax
    mov ax, start_column
    mov temp_column, ax

    mov ah, 0ch
    mov al, cur_color
    mov bh, our_page
@@loop:
    mov cx, temp_column
    mov dx, temp_line
    int 10h

    dec temp_position_x
    inc temp_column
    cmp temp_position_x, 0
    jnz @@loop

    dec temp_position_y
    inc temp_line
    mov cx, cur_point_size
    mov temp_position_x, cx

    mov cx, start_column
    mov temp_column, cx

    cmp temp_position_y, 0
    jnz @@loop

    popa; di si bp sp ax

    ret
draw_point endp


draw_snake proc
    mov cl, snake_length
    xor ch, ch
@@loop:
    call draw_point
    cmp is_vertical_snake, 00h
    jne @@vert_snake
    add start_column, 5
    jmp @@next
@@vert_snake:
    add start_line, 5

@@next:
    mov ax, 4
    mov cur_point_size, ax
    dec cx
    test cx, cx
    jne @@loop
    ret
draw_snake endp

init_snake proc
    mov al, 1
    mov di, offset map
    add di, 30
    add di, 20*64
    stosb
    stosb
    stosb
    stosb

    mov head_x, 30
    mov head_y, 20
    mov tail_x, 33
    mov tail_y, 20


    mov al, head_x
    mov bl, 05h
    mul bl
    mov start_column, ax
    mov al, head_y
    mul bl
    mov start_line, ax

    mov ax, snake_point_size
    mov cur_point_size, ax

    mov al, snake_color
    mov cur_color, al
    call draw_snake
    ret
init_snake endp

main:
    push es
    mov ah, 35h
    mov al, 08h
    int 21h
    mov word ptr old_08_code + 1, bx
    mov word ptr old_08_code + 3, es
    mov dx, offset m08_handler
    mov ah, 25h
    mov al, 08h
    int 21h
    pop es

    call change_mode

    call init_snake


    mov ah, 00h
    int 16h

    xor ax, ax
    mov al, [old_vm]
    push ax
    mov al, [old_page]
    push ax
    call change_vm

    push ds
    mov dx, word ptr old_08_code + 1
    mov ds, word ptr old_08_code + 3
    mov ah, 25h
    mov al, 08h
    int 21h
    pop ds

ret
snake_length        db  4h
snake_color         db  07h
snake_point_size    dw  0004h
cur_point_size      dw  ?
cur_color           db  ?
temp_position_x     dw  ?
temp_position_y     dw  ?
temp_point          db  ?
start_column        dw  ?
start_line          dw  ?
is_vertical_snake   db  00h
temp_line           dw  ?
temp_column         dw  ?

map:                db 40*64 dup(0)
direct              db  0   ; 0  <-
                            ; 1 up
                            ; 2 ->
                            ; 3 down
direct_tail         db  0
head_x              db  ?
head_y              db  ?
tail_x              db  ?
tail_y              db  ?



old_vm              db  ?
old_page            db  ?
old_08_code         db  0eah, 00, 00, 00, 00
our_vm              db  13h
our_page            db  00h
;размер экрана - 320*200
;размер карты - 40*64

end start