dos33fsprogs/fire/fire_tiny.s
2018-12-31 23:02:34 -05:00

200 lines
4.1 KiB
ArmAsm

; 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
; Zero Page
SEEDL = $4E
TEMP = $00
TEMPY = $01
; 100 = $64
; Soft Switches
SET_GR = $C050 ; Enable graphics
FULLGR = $C052 ; Full screen, no text
LORES = $C056 ; Enable LORES graphics
; monitor routines
GR = $F390
fire_demo:
; GR part
jsr GR ; 3
bit FULLGR ; 3
;==========
; 6
; Setup white line on bottom
lda #$ff ; 2
ldy #39 ; 2
white_loop:
sta $7d0,Y ; hline 24 (46+47) ; 3
dey ; 1
bpl white_loop ; 2
;============
; 10
fire_loop:
ldx #22 ; 22 ; 2
yloop:
stx TEMPY ; txa/pha not any better ; 2
; Self-modify the inner loop so it loads/stores from proper
; low-res address. Generate the proper row memory address
jsr get_row ; 3
sty <smc_sta+1 ; 2
sta <smc_sta+2 ; 2
inx ; 1
jsr get_row ; 3
sty <smc_lda+1 ; 2
sta <smc_lda+2 ; 2
ldy #39 ; 2
xloop:
smc_lda:
lda $7d0,Y ; load value at row+1 ; 3
pha ; save on stack ; 1
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
ror ; shift into carry ; 1
pla ; 1
bcs no_change ; 2
.byte $2c ; BIT trick, nops out next instruction ; 1
no_change:
lda <(color_progression),X ; 2
smc_sta:
sta $750,Y ; 3
dey ; 1
bpl xloop ; 2
ldx TEMPY ; 2
dex ; 1
bpl yloop ; 2
bmi fire_loop ; 2
color_progression:
.byte $00 ; 8->0 ; 1000 0101
.byte $bb ; 9->11 ; 1001 0001
.byte $00 ; 10->0 ; 1010 0000
.byte $aa ; 11->10 ; 1011 0000
.byte $00 ; 12->0 ; 1100 0000
.byte $99 ; 13->9 ; 1101 1001
.byte $00 ; 14->0 ; 1110 0000
.byte $dd ; 15->13 ; 1111 1101
; Take row X and convert to address A:Y
get_row:
; get low byte
; 000X X00O
; lsr
; 0000 XX00 O
; adc #1
; 0000 XXOx
; lsr
; 0000 0XXO
; lsr
; 0000 00XX O
; ror
txa ; 1
and #$19 ; 2
lsr ; 1
adc #1 ; 2
lsr ; 1
lsr ; 1
tay ; 1
lda <low_offsets,Y ; 2
ror ; 1
tay ; 1
;===========
; 13
; high byte of store address
txa ; 1
and #$7 ; 2
lsr ; 1
ora #$4 ; 2
;===========
; 6
rts ; 1
; 14+6 = 20, as opposed to full lookup table which would be
; at least 24
; down to 13+3 at the expense of readability
; these are shifted left by one due to the algorithm
low_offsets:
.byte $00,$50,$a0