dos33fsprogs/fire/fire_tiny.s

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; Lo-res fire animation, size-optimized
; by deater (Vince Weaver) <vince@deater.net>
; based on code described here http://fabiensanglard.net/doom_fire_psx/
; 611 bytes at first
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; 601 bytes -- strip out some unused code
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; 592 bytes -- don't init screen
; 443 bytes -- remove more dead code
; 206 bytes -- no need to clear screen
; 193 bytes -- un-cycle exact the random16 code
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; 189 bytes -- more optimization of random16 code
; 161 bytes -- move to 8-bit RNG
; 152 bytes -- reduce lookup to top half colors (had to remove brown)
; also changed maroon to pink
; 149 bytes -- use monitor GR
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; Zero Page
SEEDL = $4E
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TEMP = $00
TEMPY = $01
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; 100 = $64
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; Soft Switches
SET_GR = $C050 ; Enable graphics
FULLGR = $C052 ; Full screen, no text
LORES = $C056 ; Enable LORES graphics
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; monitor routines
GR = $F390
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fire_demo:
; GR part
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jsr GR ; 3
bit FULLGR ; 3
;==========
; 6
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; Setup white line on bottom
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lda #$ff ; 2
ldx #39 ; 2
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white_loop:
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sta $7d0,X ; hline 24 (46+47) ; 3
dex ; 1
bpl white_loop ; 2
;============
; 10
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fire_loop:
ldy #44 ; 22 * 2
yloop:
lda gr_offsets,Y
sta smc2+1
lda gr_offsets+1,Y
sta smc2+2
lda gr_offsets+2,Y
sta smc1+1
lda gr_offsets+3,Y
sta smc1+2
sty TEMPY
ldx #39
xloop:
smc1:
lda $7d0,X
sta TEMP
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and #$7 ; mask off
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tay
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;=============================
; 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:
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lda SEEDL
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beq doEor
asl
beq noEor ; if the input was $80, skip the EOR
bcc noEor
doEor: eor #$1d
noEor: sta SEEDL
; end inlined RNG
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and #$1
beq no_change
decrement:
lda color_progression,Y
jmp done_change
no_change:
lda TEMP
done_change:
smc2:
sta $750,X
dex
bpl xloop
ldy TEMPY
dey
dey
bpl yloop
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bmi fire_loop
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color_progression:
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.byte $00 ; 8->0 ; 1000 0101
.byte $bb ; 9->11 ; 1001 0001
.byte 0 ; 10->0 ; 1010 0000
.byte $aa ; 11->10 ; 1011 0000
.byte 0 ; 12->0 ; 1100 0000
.byte $99 ; 13->9 ; 1101 1001
.byte $00 ; 14->0 ; 1110 0000
.byte $dd ; 15->13 ; 1111 1101
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gr_offsets:
.word $400,$480,$500,$580,$600,$680,$700,$780
.word $428,$4a8,$528,$5a8,$628,$6a8,$728,$7a8
.word $450,$4d0,$550,$5d0,$650,$6d0,$750,$7d0