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worm2.asm
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worm2.asm
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*=$1000
Const_KBD_BUFFER = $c5 ; Keyboard matrix
Const_UP = $09 ;
Const_DOWN = $0c ;values
Const_LEFT = $0a ;for up down left right
Const_RIGHT = $0d ;
Const_LEVELUP_KEY = $16 ; "T" pressed = increase length of worm
;*****************************************************
; Initialize worm memory areas
;*****************************************************
ldx #0
lda #0
loop sta worm1x,x
sta worm1y,x
inx
dex
bne loop
lda #$93 ; Clear the screen
jsr $ffd2
main_loop
lda offset
tax
lda worm1x,x
sta tempx
lda worm1y,x
sta tempy
lda #0
sta worm1x,x
sta worm1y,x
lda #$20 ; Erase starting position
pokeaxy tempx,tempy
jsr set_direction ; Change position of head
inc offset
lda headx
clc
lda offset
adc length
tax
lda headx
sta worm1x,x
lda heady
sta worm1y,x
lda #$32 ; Draw head
pokeaxy headx,heady
;*****************************************************
; finish loop
;*****************************************************
jsr get_key
jsr delay
jmp main_loop
rts
;*****************************************************
; set_direction
;*****************************************************
set_direction
lda startdir
cmp #1
beq @down
cmp #2
beq @left
cmp #3
beq @right
@up dec heady
jmp @cont
@down inc heady
jmp @cont
@left dec headx
jmp @cont
@right inc headx
@cont
rts
;*****************************************************
; get input
;*****************************************************
get_key lda Const_KBD_BUFFER ; Input a key from Keyboard
sta $400
_ck_pressed
cmp #Const_DOWN ; down - z pressed
beq @down
cmp #Const_Right ; up - w pressed
beq @right
cmp #Const_LEFT ; left - a pressed
beq @left
cmp #Const_Up ; right - s pressed
beq @up
cmp #Const_LEVELUP_KEY ; T - Pressed - advance a level - cheat
beq @make_bigger
rts
@down
lda #1
sta startdir ; Down
rts
@right
lda #3
sta startdir ; Right
rts
@up
lda #0
sta startdir ; Up
rts
@left
lda #2
sta startdir ; left
rts
@make_bigger
inc length
ldx length
stx $403
rts
;***DELAY ***
delay txa
pha
ldx #$ff
@loop1 ldy #0
@loop2 dey
bne @loop2
dex
bne @loop1
pla
rts
tempx byte 00
tempy byte 00
headx byte 06
heady byte 10
startdir byte 01,00
offset byte 00,00
length byte 30,00
map_off_l byte $00,$28,$50,$78,$A0,$C8,$F0,$18,$40,$68,$90,$b8,$E0,$08,$30,$58,$80,$a8,$d0,$f8,$20,$48,$70,$98,$c0
map_off_h byte $04,$04,$04,$04,$04,$04,$04,$05,$05,$05,$05,$05,$05,$06,$06,$06,$06,$06,$06,$06,$07,$07,$07,$07,$07
;*****************************************************
; Grab value of screen position located at x,y
; Store result in accumulator
;*****************************************************
defm peekaxy
ldx /2 ; X value
ldy /1 ; Y Value
lda map_off_l,x ; Load map low byte into $fb
sta $fb
lda map_off_h,x ; Load map hig byte into $fc
sta $fc
lda ($fb),y ; Load result into acc
endm
;*****************************************************
; Store value of accumulator in screen memory at position
; x, y
;*****************************************************
defm pokeaxy
pha
ldx /2 ; X value
ldy /1 ; Y value
lda map_off_l,x ; Load map low byte into $fb
sta $fb
lda map_off_h,x ; Load map high byte into $fc
sta $fc
pla
sta ($fb),y ; Store result in screen memory
endm
*=$2000
worm1x
*=$2100
worm1y