mirror of
https://github.com/deater/dos33fsprogs.git
synced 2024-11-05 11:06:53 +00:00
156 lines
3.9 KiB
ArmAsm
156 lines
3.9 KiB
ArmAsm
; modified to avoid using zero-page addresses
|
|
|
|
; Apple ][ Lo-res fire animation, size-optimized to 64 bytes
|
|
|
|
; by deater (Vince Weaver) <vince@deater.net>
|
|
|
|
; originally based on code described here
|
|
; http://fabiensanglard.net/doom_fire_psx/
|
|
; but this is a slightly different algorithm (but still cool looking)
|
|
|
|
; Optimization history:
|
|
; 80 bytes -- the size of tire_tiny.s
|
|
; 64 bytes -- use the firmware SCROLL routine to handle the scrolling
|
|
; this adds some flicker but saves many bytes
|
|
; 63 bytes -- qkumba noted that SCROLL leaves BAS2L:BAS2H pointing at $7d0
|
|
; 66 bytes -- tried on real hardware. Found that the original firmware
|
|
; never sets MIXCLR on boot, and my II+ machine was leaving
|
|
; it off so for correctness need to add it on.
|
|
; 66 bytes -- wasted a lot of time trying to either find clever ways to
|
|
; get $C050/C052 accessed, or to shorten the lookup table
|
|
; in half by lsr. Nothing panned out.
|
|
; 64 bytes -- realized I could save/restore the random SEEDL on the stack!
|
|
; doesn't seem to affect the output pattern either.
|
|
|
|
|
|
; Zero Page
|
|
|
|
WNDTOP = $22
|
|
WNDBTM = $23
|
|
CV = $25
|
|
BASL = $28
|
|
BASH = $29
|
|
BAS2L = $2A
|
|
BAS2H = $2B
|
|
SEEDL = $4E
|
|
|
|
; Soft Switches
|
|
SET_GR = $C050 ; Enable graphics
|
|
MIXCLR = $C052 ; Full screen, no text at bottom
|
|
LORES = $C056 ; Enable LORES graphics
|
|
|
|
; Monitor ROM routines. Try to use well-known entry points as
|
|
; these did sometimes change with newer models
|
|
SCROLL = $FC70
|
|
VTAB = $FC22 ; takes row in CV, Result is in BASL:BASH ($28/$29)
|
|
VTABZ = $FC24 ; VTABZ variant takes row in Accumulator
|
|
|
|
fire_demo:
|
|
|
|
; Set lores graphics
|
|
|
|
bit SET_GR ; force graphics mode ; 3
|
|
; LORES and LOWSCR (lo-res page1)
|
|
; are set by the boot rom
|
|
|
|
bit MIXCLR ; want full-screen graphics w/o mixed ; 3
|
|
; text the boot process doesn't set this
|
|
; (it doesn't matter in text mode)
|
|
; and while IIe and emulators come up clear
|
|
; my Apple II+ doesn't
|
|
|
|
; Set window. This seems to be set properly at boot though
|
|
; lda #0
|
|
; sta WNDTOP
|
|
; lda #24
|
|
; sta WNDBTM
|
|
|
|
|
|
scroll_loop:
|
|
|
|
jsr SCROLL ; scrolls screen up one row ; 3
|
|
|
|
|
|
;======================================
|
|
; re-draw bottom line (row 23) as white
|
|
|
|
|
|
; Y is left at 40 after SCROLL
|
|
; also BAS2L:BAS2H is left at $7d0
|
|
; this code over-writes $7F8 (the MSLOT screen hole value)
|
|
; but this should not matter for this demo
|
|
|
|
lda #$ff ; top/bottom white ; 2
|
|
w_loop:
|
|
sta (BAS2L),Y ; hline 23 (46+47) ; 2
|
|
dey ; 1
|
|
bpl w_loop ; 2
|
|
;============
|
|
; 8
|
|
|
|
fire_loop:
|
|
|
|
lda #22 ; start at line 22 ; 2
|
|
sta CV ; store in Row location ; 2
|
|
|
|
yloop:
|
|
; puts address of row CV into BASL:BASH
|
|
jsr VTAB ; 3
|
|
|
|
|
|
; loop for X values 39 ... 0
|
|
ldy #39 ; 2
|
|
xloop:
|
|
|
|
;=============================
|
|
; random8
|
|
;=============================
|
|
; 8-bit 6502 Random Number Generator
|
|
; Linear feedback shift register PRNG by White Flame
|
|
; http://codebase64.org/doku.php?id=base:small_fast_8-bit_prng
|
|
|
|
random8:
|
|
pla
|
|
; lda SEEDL ; 2
|
|
beq doEor ; 2
|
|
asl ; 1
|
|
beq noEor ; if the input was $80, skip the EOR ; 2
|
|
bcc noEor ; 2
|
|
doEor: eor #$1d ; 2
|
|
noEor: ;sta SEEDL ; 2
|
|
pha
|
|
|
|
; end inlined RNG
|
|
|
|
; Randomly either use current value, or decay by one
|
|
bmi no_change ; assume bit 7 is as random as bit 0 ; 2
|
|
|
|
; Lookup the new color in table
|
|
lda (BASL),Y ; load value ; 2
|
|
and #$7 ; mask off ; 2
|
|
tax ; 1
|
|
; lda <(color_progression),X ; 2
|
|
lda color_progression,X ; 3
|
|
sta (BASL),Y ; 2
|
|
no_change:
|
|
|
|
dey ; 1
|
|
bpl xloop ; 2
|
|
|
|
dec CV ; 2
|
|
|
|
bpl yloop ; 2
|
|
|
|
bmi scroll_loop ; 2
|
|
|
|
color_progression:
|
|
.byte $00 ; 8->0 ; 1000 -> 0000 ; needed
|
|
.byte $bb ; 9->11 ; 1001 -> 1011
|
|
.byte $00 ; 10->0 ; 1010 -> 0000 ; needed
|
|
.byte $aa ; 11->10 ; 1011 -> 1010
|
|
.byte $00 ; 12->0 ; 1100 -> 0000 ; don't care
|
|
.byte $99 ; 13->9 ; 1101 -> 1001
|
|
.byte $00 ; 14->0 ; 1110 -> 0000 ; don't care
|
|
.byte $dd ; 15->13 ; 1111 -> 1101
|
|
|