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snake.asm
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; https://www.tutorialspoint.com/assembly_programming/assembly_registers.htm
; http://spike.scu.edu.au/~barry/interrupts.html#ah02
; http://studianet.pl/kursy/proki/podst_asemblera/podst_asem.htm
; http://www.oldlinux.org/Linux.old/docs/interrupts/int-html/int-15.htm
; https://en.wikipedia.org/wiki/INT_16H
; http://www.ctyme.com/intr/cat.htm
assume cs:code
data segment
assume ds:data
star_pos db 0
snake_pos db 0
snake_pos_x db 0
snake_direction db 1
cursor_pos db 0
cursor_pos_x db 0
body db 12 dup(0)
data ends
code segment
; set data segment pointer
push ax
mov ax, data
mov ds, ax
pop ax
; text mode 80x25, 16 colors, 8 pages
; ah=xxh al=03h -> ax=xx03h
; int 10h = video card intterupt
mov ah, 00h
mov al, 03h
int 10h
start:
; set values initially
mov star_pos, 35
mov snake_pos, 55
mov snake_pos_x, 5
game_loop:
check_key:
; sleep for 20ms (20816 microseconds -> 0c680h)
mov cx, 01h
mov dx, 0c680h
mov ah, 86h
int 15h
; check if any data is in keyboard buffer
mov ah, 0Bh
int 21h
cmp al, 0h
je is_new_key_false
is_new_key_true:
; if there is some data in keyboard buffer
; get keystroke and save ASCII character in AL, AH = scan code
mov ah, 0
int 16h
; check if esc is pressed
cmp ah, 01h
jne not_exit
jmp game_over
not_exit:
; check if W is pressed
cmp ah, 11h
jne not_w
mov snake_direction, 0
not_w:
; check if S is pressed
cmp ah, 1Fh
jne not_s
mov snake_direction, 2
not_s:
; check if A is pressed
cmp ah, 1Eh
jne not_a
mov snake_direction, 3
not_a:
; check if D is pressed
cmp ah, 20h
jne not_d
mov snake_direction, 1
not_d:
; flush keyboard buffer
mov ah, 0Ch
int 21h
is_new_key_false:
set_new_head_position:
cmp snake_direction, 0
jne not_up
sub snake_pos, 10
not_up:
cmp snake_direction, 1
jne not_right
inc snake_pos
inc snake_pos_x
not_right:
cmp snake_direction, 2
jne not_down
add snake_pos, 10
not_down:
cmp snake_direction, 3
jne not_left
dec snake_pos
dec snake_pos_x
not_left:
cmp snake_pos_x, 11
jne not_over_right
mov snake_pos_x, 1
sub snake_pos, 10
not_over_right:
cmp snake_pos_x, 0
jne not_over_left
mov snake_pos_x, 10
add snake_pos, 10
not_over_left:
cmp snake_pos, 100
jle not_over_bottom
cmp snake_pos, 110
jg not_over_bottom
sub snake_pos, 100
not_over_bottom:
cmp snake_pos, 244
jl not_over_top
cmp snake_pos, 0
jg not_over_top
add snake_pos, 100
not_over_top:
; loop for each part of body defined in body array
mov si, 0
loop_over_body_collision:
; if si is outer of body
cmp si, 11
jge exit_loop_over_body_collision
mov ah, [snake_pos]
mov bh, body[si]
cmp ah, bh
jne not_collided
jmp game_over
not_collided:
inc si
jmp loop_over_body_collision
exit_loop_over_body_collision:
mov si, 0
loop_over_body_shift:
; if si is outer of body
cmp si, 11
jge exit_loop_over_body_shift
inc si
mov ah, body[si]
dec si
mov body[si], ah
; move si to next value
inc si
jmp loop_over_body_shift
exit_loop_over_body_shift:
; insert new body part (twice if star has been collected)
mov si, 0
loop_over_body_add_body:
; if si is outer of body
cmp si, 11
jge exit_loop_over_body_add_body
mov dl, body[si]
cmp dl, 0
jne dont_add_body
mov dl, snake_pos
mov body[si], dl
; check if head is euqal to star position
; and insert body once again
mov ah, [snake_pos]
mov bh, [star_pos]
cmp ah, bh
jne exit_loop_over_body_add_body
inc si
cmp si, 11
jge exit_loop_over_body_add_body
mov dl, body[si]
cmp dl, 0
jne dont_add_body
mov dl, snake_pos
mov body[si], dl
jmp exit_loop_over_body_add_body
dont_add_body:
; move si to next value
inc si
jmp loop_over_body_add_body
exit_loop_over_body_add_body:
render:
mov cursor_pos, 0
; print score
mov dl, snake_pos_x
add dl, '0'
mov ah, 06h
int 21h
; set cursor at x=dl=0, y=dh=0
mov dl, 00h
mov dh, 00h
mov ah, 2h
mov bh, 0
int 10h
new_line:
mov dl, 10
mov ah, 06h
int 21h
mov dl, 13
int 21h
mov cursor_pos_x, 0
render_process:
inc cursor_pos
inc cursor_pos_x
mov ah, [cursor_pos]
mov bh, [snake_pos]
cmp ah, bh
jne render_2
mov dl, 219
mov ah, 06h
int 21h
jmp render_after
render_2:
mov si, 0
loop_over_body_render:
; if si is outer of body
cmp si, 11
jge exit_loop_over_body_render
; check if current body part
; is equal to cursor position
; and draw snake body
mov ah, [cursor_pos]
mov bh, body[si]
cmp ah, bh
jne loop_over_body_render_next
; or 219
mov dl, 219
mov ah, 06h
int 21h
jmp render_after
; move si to next value
loop_over_body_render_next:
inc si
jmp loop_over_body_render
exit_loop_over_body_render:
render_3:
mov ah, [cursor_pos]
mov bh, [star_pos]
cmp ah, bh
jne render_4
mov dl, '*'
mov ah, 06h
int 21h
jmp render_after
render_4:
mov dl, ','
mov ah, 06h
int 21h
render_after:
cmp cursor_pos_x, 10
je new_line
cmp cursor_pos, 100
jl render_process
jmp game_loop
game_over:
mov ah, 4ch
int 21h
code ends
end ;code