name "snake"
org
100h
; jump over data section:
jmp
start
; ------ data section ------
s_size
equ
7
; the snake coordinates
; (from head to tail)
; low byte is left, high byte
; is top - [top, left]
snake dw s_size dup(0)
tail
dw
?
; direction constants
;
(bios key codes):
left
equ
4bh
right
equ
4dh
up
equ
48h
down
equ
50h
; current snake direction:
cur_dir db
right
wait_time dw
0
; welcome message
msg
db "==== how to play ====", 0dh,0ah
db "this game was debugged on emu8086", 0dh,0ah
db "but it is not designed to run on the emulator", 0dh,0ah
db "because it requires relatively fast video card and cpu.", 0dh,0ah, 0ah
db "if you want to see how this game really works,", 0dh,0ah
db "run it on a real computer (click external->run from the menu).", 0dh,0ah, 0ah
db "you can control the snake using arrow keys", 0dh,0ah
db "all other keys will stop the snake.", 0dh,0ah, 0ah
db "press esc to exit.", 0dh,0ah
db "====================", 0dh,0ah, 0ah
db "press any key to start...$"
; ------ code section ------
start:
; print welcome message:
mov dx, offset msg
mov ah, 9
int 21h
; wait for any key:
mov ah, 00h
int 16h
; hide text cursor:
mov
ah, 1
mov
ch, 2bh
mov
cl, 0bh
int
10h
game_loop:
; === select first video page
mov
al, 0
; page number.
mov
ah, 05h
int
10h
; === show new head:
mov
dx, snake[0]
; set cursor at dl,dh
mov
ah, 02h
int
10h
; print '*' at the location:
mov
al, '*'
mov
ah, 09h
mov
bl, 0eh ; attribute.
mov
cx, 1
; single char.
int
10h
; === keep the tail:
mov
ax, snake[s_size * 2 - 2]
mov
tail, ax
call
move_snake
; === hide old tail:
mov
dx, tail
; set cursor at dl,dh
mov
ah, 02h
int
10h
; print ' ' at the location:
mov
al, ' '
mov
ah, 09h
mov
bl, 0eh ; attribute.
mov
cx, 1
; single char.
int
10h
check_for_key:
; === check for player commands:
mov
ah, 01h
int
16h
jz
no_key
mov
ah, 00h
int
16h
cmp
al, 1bh
; esc - key?
je
stop_game
;
mov
cur_dir, ah
no_key:
; === wait a few moments here:
; get number of clock ticks
; (about 18 per second)
; since midnight into cx:dx
mov
ah, 00h
int
1ah
cmp
dx, wait_time
jb
check_for_key
add
dx, 4
mov
wait_time, dx
; === eternal game loop:
jmp
game_loop
stop_game:
; show cursor back:
mov
ah, 1
mov
ch, 0bh
mov
cl, 0bh
int
10h
ret
; ------ functions section ------
; this procedure creates the
; animation by moving all snake
; body parts one step to tail,
; the old tail goes away:
; [last part (tail)]-> goes away
; [part i] -> [part i+1]
; ....
move_snake proc near
; set es to bios info segment:
mov
ax, 40h
mov
es, ax
; point di to tail
mov
di, s_size * 2 - 2
; move all body parts
; (last one simply goes away)
mov
cx, s_size-1
move_array:
mov
ax, snake[di-2]
mov
snake[di], ax
sub
di, 2
loop
move_array
cmp
cur_dir, left
je
move_left
cmp
cur_dir, right
je
move_right
cmp
cur_dir, up
je
move_up
cmp
cur_dir, down
je
move_down
jmp
stop_move
; no direction.
move_left:
mov
al, b.snake[0]
dec
al
mov
b.snake[0], al
cmp
al, -1
jne
stop_move
mov
al, es:[4ah]
; col number.
dec
al
mov
b.snake[0], al
; return to right.
jmp
stop_move
move_right:
mov
al, b.snake[0]
inc
al
mov
b.snake[0], al
cmp
al, es:[4ah]
; col number.
jb
stop_move
mov
b.snake[0], 0
; return to left.
jmp
stop_move
move_up:
mov
al, b.snake[1]
dec
al
mov
b.snake[1], al
cmp
al, -1
jne
stop_move
mov
al, es:[84h]
; row number -1.
mov
b.snake[1], al
; return to bottom.
jmp
stop_move
move_down:
mov
al, b.snake[1]
inc
al
mov
b.snake[1], al
cmp
al, es:[84h]
; row number -1.
jbe
stop_move
mov
b.snake[1], 0
; return to top.
jmp
stop_move
stop_move:
ret
move_snake endp
2007-07-02 14:47
