用nasm x86汇编给ms-dos系统写了一个软盘引导扇区贪吃蛇小游戏。问题是重新开始游戏后分数不会归零。
目前尝试过
mov dword [current_score], 0
但是并没有用。我能想到其他的解决方案都会使编译后的代码超过512字节的限制。不知道有没有佬有办法解决。
org 0x7C00
use16
start_point:
initialize_system:
xor ax, ax
mov ds, ax
mov es, ax
mov ss, ax
mov sp, 0x7C00
clear_screen:
mov ax, 0xB800
mov es, ax
mov ax, 3
int 0x10
inc ah
mov cx, 0x2000
int 0x10
xor di, di
mov cx, (160*25)/2
mov ax, 0x0720
pusha
rep stosw
setup_game_state:
mov di, tick_counter
stosd
stosd
mov ax, (160*25)/2
stosw
add al, 4
stosw
add al, 4
stosw
mov al, 0xFF
out 0x60, al
in al, 0x61
and al, 0xFC
out 0x61, al
mov di, (160*12) + 80
mov [snake_ptr], di
draw_game_border:
mov ax, 0x072A
mov cx, 38
mov di, (160*4)+40
rep stosw
mov cx, 16
border_draw_loop:
stosw
pusha
mov cx, 41
xor ah, ah
rep stosw
mov ah, 0x07
stosw
popa
add di, 158
loop border_draw_loop
mov cx, 38
mov di, (160*20)+42
rep stosw
display_texts:
mov di, (160*3)+42
mov si, title_text
call render_text
mov si, score_text
mov di, (160*3)+94
call render_text
mov si, control_text
mov di, (160*21)+42
call render_text
main_game_loop:
prepare_game:
popa
mov di, cx
mov si, initial_snake
call render_text
mov bp, 6
call spawn_food
game_delay:
xor eax, eax
int 0x1A
mov ax, cx
shl eax, 16
mov ax, dx
mov ebx, eax
sub eax, [tick_counter]
cmp eax, 3
jl game_delay
mov [tick_counter], ebx
in al, 0x60
handle_input:
cmp al, 177
je start_point
and al, 0x7F
cmp al, 17
je move_up
cmp al, 30
je move_left
cmp al, 31
je move_down
cmp al, 32
jne game_delay
move_right:
mov al, '>'
add di, 4
jmp execute_move
move_up:
mov al, '|'
sub di, 160
jmp execute_move
move_down:
mov al, '|'
add di, 160
jmp execute_move
move_left:
mov al, '<'
sub di, 4
execute_move:
cmp byte [es:di], '@'
sete ah
je safe_move
cmp byte [es:di], ' '
jne game_over
safe_move:
stosb
dec di
pusha
push es
push ds
pop es
mov cx, bp
inc cx
mov si, snake_ptr
add si, bp
mov di, si
inc di
inc di
std
rep movsb
cld
pop es
popa
push di
mov [snake_ptr], di
mov di, [snake_ptr+2]
mov al, '*'
stosb
cmp ah, 1
je handle_food
mov di, [snake_ptr + bp]
mov al, ' '
stosb
jmp continue_game
handle_food:
inc bp
inc bp
mov di, (160*3)+114
add dword [current_score], 1
mov ax, [current_score]
mov bl, 10
update_score_display:
div bl
xchg al, ah
add al, '0'
stosb
dec di
dec di
dec di
mov al, ah
xor ah, ah
or al, al
jnz update_score_display
call spawn_food
continue_game:
pop di
jmp game_delay
game_over:
mov di, (160*19)+92
mov si, gameover_text
call render_text
wait_for_restart:
in al, 0x60
cmp al, 177
jne wait_for_restart
jmp start_point
spawn_food:
pusha
xor eax, eax
xor bl, bl
int 0x1A
spawn_seed:
xor eax, eax
xor bl, bl
int 0x1A
random_position:
cmp bl, 5
jg spawn_seed
mov ax, dx
mov cx, 75
mul cx
movzx edx, dx
mov ecx, 65537
div ecx
mov ax, dx
shr edx, 16
mov ecx, (160*20)
div cx
and dl, 0xFC
inc bl
cmp dx, (160*5)
jl random_position
mov di, dx
cmp byte [es:di], 0x20
jne random_position
mov al, '@'
stosb
popa
ret
render_text:
pusha
render_loop_text:
lodsb
or al, al
jz render_done_text
stosb
inc di
jmp render_loop_text
render_done_text:
popa
ret
title_text: db 'Snake',0
control_text: db 'WASD, N - restart',0
gameover_text: db 'Game Over',0
score_text: db 'Score:',0
initial_snake: db ' ',0
times 510-($-$$) db 0
dw 0xAA55
section .bss
tick_counter: resd 1
current_score: resd 1
snake_ptr: resd 1
