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|
;
; Simple starfield effect
;
stars_update:
ld x, <stars
ld a, >stars
stars_update_loop:
ld y, [a : x]
inc x
bo
inc a
ld b, [a : x]
; is the end of list?
cmp b, 0xff
bz
ret
push a
push x
; erase old
ld x, 0
ld [b : y], x
ld x, [sp + 0]
; update address
inc x
bo
inc a
push x
ld x, [a : x]
stars_update_addr:
add y, 128
bo
inc b
cmp b, 0xfe
bnz
jmp stars_no_wrap
cmp y, 0x80
bc
ld b, 0xbf
; add some randomness
push a
push x
push b
call rnd
pop b
pop x
pop a
stars_no_wrap:
dec x
bnz
jmp stars_update_addr
pop x
; draw new: color
inc x
bo
inc a
ld x, [a : x]
ld [b : y], x
pop x
pop a
; save new address
ld [a : x], b
dec x
bo
dec a
ld [a : x], y
; next star
add x, 4
bo
inc a
jmp stars_update_loop
|
