So for some reason I had the idea that I wanted to make a version of snake that fit within 256 bytes, in assembly. I ended up with this!

I spent a few hours optimizing and adding some minor features, and now here's the new version

I of course have a wait loop to slow it down because otherwise it's unplayably fast. (it almost is too fast as it is)

I'm quite happy with how it turned out, even getting a score counter in there.
Here's the source (assembled with BRASS). It's not very well commented but tomorrow I'll see if I can comment it up for you. I'll also upload it to the archives if anyone wants to try it.


#include ""
#include ""
.variablename SNAKE
.org UserMem - 2
.db t2ByteTok, tAsmCmp
    xor d
    jr main
    .dw 0000h ;Description
    .db $07, $00
    .dw 0000h ;Icon
    .dw 0000h ;ALE

.dw $BEEF ;I have 2 extra bytes left, everyone loves beef!

;Positioning is important here.
;I want to be able to inc my way from FOOD_POS to HEAD_POS,
;from HEAD_OFF to TAIL_OFF, from GROWTH to BSIZE, from BODY_X to BODY_Y
;I also want to be able to dec from GROWTH to TAIL_OFF
FOOD_POS = saveSScreen

HEAD_POS = saveSScreen + 2

HEAD_OFF = saveSScreen + 4
TAIL_OFF = saveSScreen + 5

GROWTH = saveSScreen + 6
BSIZE = saveSScreen + 7

VEL = saveSScreen + 8
VEL_X = VEL + 1

TEXT = saveSScreen + 10

BODY_X = 8000h ;appData
BODY_Y = 8100h ;ramCode

INITIAL_LEN = 4 ;First food gen increases to 5

    ld hl,InitialData
    ld de,HEAD_POS
    ld bc,InitialDataEnd - InitialData
    set textWrite, (iy + sGrFlags)

    ;Draw border of board
    ld hl,64 << 8 ;X=64,Y=0
    ld d,h ;X=64,Y=64
    ld e,h
    call fastlineb
    call growAndGenFood

    ld de,0

    cp skClear
    ret z
    dec a ;Down key
    jr nz,$+3
    inc e

    dec a ;Left key
    jr nz,$+3
    dec d

    dec a ;Right key
    jr nz,$+3
    inc d

    dec a ;Up key
    jr nz,$+3
    dec e

    dec a ;Wrap around from up key
    cp 252 ;If Down was pressed, A will be 252. If it's less, ignore key press
    jr c,noInput

    ld hl,VEL_Y
    ld a,(hl)
    and e
    jr nz,{@}
    ld (hl),e

    inc hl ;VEL_X
    ld a,(hl)
    and d
    jr nz,{@}
    ld (hl),d
    ld hl,(VEL) ;H = VelX, L = VelY

    ld de,HEAD_POS+1 ;HEAD_X
    ld a,(de)
    add a,h
    and 31 ;Clamp X to board (wall wraparound)
    ld h,a
    ld (de),a

    dec de ;HEAD_Y
    ld a,(de)
    add a,l
    and 31 ;Clamp Y to board (wall wraparound)
    ld l,a
    ld (de),a

    ld de,(FOOD_POS)
    call cphlde ;Test if head position = food position
    push af ;Save flag for decided whether or not to fill in head
    push hl ;Save head position

    ld bc,noCollisionCheck ;Save return spot to stack
    push bc
    jr z,growAndGenFood ;Jump to growAndGenFood if head pos == food pos

;No food gen, so check for collision. HL contains head position
    add hl,hl
    call pixeltesthl
    ret z ;noCollisionCheck is still on stack, so we can use this to jump to it if we didn't collide

;End game due to collision
    ;Pop return addr, head pos, flags
    pop hl
    pop hl
    pop hl

    ld hl,GROWTH
    dec (hl)
    jr nz,{@}
    inc (hl)
    dec hl ;HL = TAIL_OFF
    inc (hl)
    call DispBodyPart

    pop de ;Current head position

    ld hl,HEAD_OFF
    inc (hl)
    ld c,(hl)
    ld b,BODY_X >> 8
    ld a,d
    ld (bc),a

    inc b
    ld a,e
    ld (bc),a
    pop af ;Z will be set if we ate food
    call nz,DispBodyPart
    call ifastcopy ;re-enables interrupts

    ld a,1800/22
    djnz $+0
    dec a
    jr nz,{-1@}
    jr gameLoop

    ;Set pen position for displaying score
    ld hl,(4 << 8) | 70 ;32 = pen row, 70 = pen col
    ld (penCol),hl

    ld hl,GROWTH
    inc (hl)

    ;Increment and display score
    inc hl ;HL = BSIZE (score)
    inc (hl)
    ld l,(hl)
    ld h,0
    call VDispHL
    ;End of display score
    ld c,31 ;Mask for values 0-31
    call rand127 ;Y value
    and c
    ld l,a

    call rand127 ;X value
    and c
    ld h,a

    push hl
    add hl,hl
    call pixeltesthl
    pop hl ;H = x, L = y
    jr nz,genFood
    ld (FOOD_POS),hl ;Save food position
    ;Fall down to DispSquare

;HL = X/Y in squares
    add hl,hl ;Convert to pixels
    ld a,h ;iputsprite takes X in A
    ld b,2
    ld ix,SquareSprite
    jp iputsprite

;Displays a body part, offset is given in A
    ld a,(hl)
    ld h,BODY_X >> 8
    ld l,a ;HL = BODY_X + OFFSET
    ld a,(hl)

    inc h ;HL = BODY_Y + OFFSET
    ld l,(hl) ;Y
    ld h,a
    jr DispSquare ;also HEAD_Y/HEAD_X
;    .db 0 ;HEAD_Y
;    .db -1 ;HEAD_X
;It doesn't matter what HEAD_OFF and TAIL_OFF are as long as
;they are the same, why not also use it as sprite data
    .db %11000000 ;HEAD_OFF
    .db %11000000 ;TAIL_OFF
    .db INITIAL_LEN + 1 ;GROWTH (In the code a growth of 1 means no growth, so we add 1 to get desired growth)
    .db 0 ;VEL_Y
    .db 1 ;VEL_X
Well done, you whipped that up fast and the result is impressive Smile.
Now that's impressive Razz Now Tunnel ! Very Happy
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