dos33fsprogs/demos/fire/cool_effect.s
Vince Weaver b1238af49d re-arranged the entire directory structure
this will probably upset people
2021-01-05 15:29:31 -05:00

155 lines
3.0 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
; 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 #44 ; 22 * 2 ; 2
yloop:
; low bytes of address
lda <gr_offsets,X ; 2
sta <smc2+1 ; 2
lda <gr_offsets+2,X ; 2
sta <smc1+1 ; 2
dec <smc2+2
dec <smc1+2
stx TEMPY ; txa/pha not any better ; 2
; high bytes of address
; lda <gr_offsets+1,X ; 2
; sta <smc2+2 ; 2
ldx <smc2+2 ; 2
dex ; 1
txa ; 1
ora #$4 ; make sure it's 4-7 ; 2
sta <smc2+2 ; 2
lda <gr_offsets+3,X ; 2
sta <smc1+2 ; 2
ldy #39 ; 2
xloop:
smc1:
lda $7d0,Y ; 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
beq doEor
asl
beq noEor ; if the input was $80, skip the EOR
bcc noEor
doEor: eor #$1d
noEor: sta SEEDL
; end inlined RNG
ror ; shift into carry ; 1
pla ; 1
bcs no_change ; 2
.byte $2c ; BIT trick, nops out next instruction
no_change:
lda <color_progression,X ; 2
smc2:
sta $750,Y ; 3
dey ; 1
bpl xloop ; 2
ldx TEMPY
dex
dex
bpl yloop
bmi fire_loop
color_progression:
.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
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