dos33fsprogs/demos/fire/fire_firmware.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
; 601 bytes -- strip out some unused code
; 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
; 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
; 149 bytes -- load into zero page
; 140 bytes -- start using zero-page addressing
; 139 bytes -- rotate instead of mask for low bit
; 138 bytes -- bcs instead of jmp
; 137 bytes -- BIT nop trick to get rid of jump
; 135 bytes -- push/pull instead of saving to zero page
; 134 bytes -- replace half of lookup table with math
; 119 bytes -- replace that half of lookup table with better math
; 134 bytes -- replace other half of lookup table with math
; 132 bytes -- replace stack with zp loads
; 129 bytes -- use Y instead of X
; 125 bytes -- optimize low byte generationw with branch
; 113 bytes -- make get_row a subroutine
; 112 bytes -- regrettable change to the low-byte code
; 109 bytes -- replace BIT/OR in low calc with an ADC
; 107 bytes -- replace self-modifying load/store absolute with Y-indirect
; 106 bytes -- assume bit 8 is as random as bit 0
2019-01-03 02:57:40 +00:00
; 82 bytes -- use VTAB in firmware to setup addresses
; (Antoine Vignau on comp.sys.apple2 reminded me of this)
; 81 bytes -- qkumba points out that GR leaves BASL:BASH pointing at line 23
; so we can use Y-indirect of BASL to draw the bottom white line
; 83 bytes -- remove use of X as counter, use CV instead
2019-01-03 04:42:41 +00:00
; 83 bytes -- tried flipping x/y loops in case it allowed more optimization
; but the display runs way too slow in that case
; 81 bytes -- call LF to increment CV + VTAB all at once
2019-01-03 05:10:59 +00:00
; 80 bytes -- re-arrange how the random stuff happens. remove last BIT hack
; Zero Page
SEEDL = $4E
TEMP = $00
TEMPY = $01
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OUTL = $04
OUTH = $05
CV = $25
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BASL = $28
BASH = $29
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H2 = $2C
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COLOR = $30
; 100 = $64
; Soft Switches
SET_GR = $C050 ; Enable graphics
FULLGR = $C052 ; Full screen, no text
LORES = $C056 ; Enable LORES graphics
; monitor routines
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ASOFT_GR = $F390
MON_SETGR = $FB40
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; VTAB notes
; if Applesoft ROM, we can jump to ASOFT_VTAB which takes value in X
; this won't work on the original Apple II with Integer ROM
; we can jum to MON.TABV instead but then have to copy the value
; to Accumulator first
; This ovewrites CV (25)
; Result is in BASL:BASH (28/29)
ASOFT_VTAB = $F25A
MON_TABV = $FB5B
VTAB = $FC22
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LF = $FC66
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fire_demo:
; GR part
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jsr MON_SETGR ; 3
bit FULLGR ; 3
;==========
; 6
; Setup white line on bottom
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; note: calling HLINE in firmware would take at least 13 bytes
; below code is 9
; we depend on the call to MON_SETGR leaving BASL:BASH set for line 39
; (thanks to qkumba)
2019-01-03 02:57:40 +00:00
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CLEOL2 = $FCA0 ; on original II, they got rid of it on IIe :(
; lda #$ff ; 2 bytes shorter on II/II+
; ldy #0
; jsr CLEOL2
lda #$ff ; 2
ldy #39 ; 2
white_loop:
sta (BASL),Y ; hline 23 (46+47) ; 2
dey ; 1
bpl white_loop ; 2
;============
; 9
fire_loop:
lda #22 ; start at line 22 ; 2
sta CV ; ; 2
yloop:
; setup the load/store addresses
; using Y-indirect is smaller than self-modifying code
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; setup destination to write to (CV) in OUTL:OUTH
jsr VTAB ; 3
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lda BASL ; 2
sta OUTL ; 2
lda BASH ; 2
sta OUTH ; 2
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; setup source to read from in (CV+1) in BASL:BASH
jsr LF ; this increments CV and calls VTAB
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dec CV ; restore CV ; 2
ldy #39 ; 2
xloop:
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lda (BASL),Y ; load value at row+1 ; 2
sta (OUTL),Y ; 2
and #$7 ; mask off ; 2
tax ; 1
;=============================
; 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:
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
; end inlined RNG
bmi no_change ; assume bit 7 is as random as bit 0 ; 2
lda <(color_progression),X ; 2
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sta (OUTL),Y ; 2
no_change:
dey ; 1
bpl xloop ; 2
dec CV ; 2
bpl yloop ; 2
bmi fire_loop ; 2
color_progression:
.byte $00 ; 8->0 ; 1000 0000
.byte $bb ; 9->11 ; 1001 1011
.byte $00 ; 10->0 ; 1010 0000
.byte $aa ; 11->10 ; 1011 1010
.byte $00 ; 12->0 ; 1100 0000
.byte $99 ; 13->9 ; 1101 1001
.byte $00 ; 14->0 ; 1110 0000
.byte $dd ; 15->13 ; 1111 1101