dos33fsprogs/basic/two-liners/entropy_tiny.s
2021-03-04 20:44:08 -05:00

123 lines
2.2 KiB
ArmAsm

; Entropy
; by Dave McKellar of Toronto
; Two-line BASIC program
; Found on Beagle Brother's Apple Mechanic Disk
; Converted to 6502 Assembly by Deater (Vince Weaver) vince@deater.net
; 24001 ROT=0:FOR I=1 TO 15: READ A,B: POKE A,B: NEXT: DATA
; 232,252,233,29,7676,1,7678,4,7679,0,7680,18,7681,63,
; 7682,36,7683,36,7684,45,7685,45,7686,54,7687,54,7688,63,
; 7689,0
; 24002 FOR I=1 TO 99: HGR2: FOR E=.08 TO .15 STEP .01:
; FOR Y=4 to 189 STEP 6: FOR X=4 to 278 STEP 6:
; SCALE=(RND(1)<E)*RND(1)*E*20+1: XDRAW 1 AT X,Y:
; NEXT: NEXT: NEXT: NEXT
; SCALE=(RND(1)<E)*RND(1)*E*20+1
;
; Equivalent to IF RND(1)<E THEN SCALE=RND(1)*E*20+1
; ELSE SCALE=1
; What this does:
; if EPOS is 8,9 then value is either 1 or 2
; if EPOS is 10,11,12,13,14 then value is either 1, 2, or 3
; Optimization
; 88 bytes -- hack up the entropy code
; 83 bytes -- count down YPOS instead of up
; 73 bytes -- XPOS only up to 256
; 73 bytes -- move to zero page
; 65 bytes -- move XPOS/YPOS into X/Y, use RESTORE
;BLT=BCC, BGE=BCS
; zero page locations
HGR_SHAPE = $1A
A5H = $45
XREG = $46
YREG = $47
HGR_SCALE = $E7
HGR_ROTATION = $F9
FRAME = $FC
XPOS = $FD
YPOS = $FF
; ROM calls
HGR2 = $F3D8
HPOSN = $F411
XDRAW0 = $F65D
RESTORE = $FF3F
.zeropage
entropy:
jsr HGR2 ; Hi-res graphics, no text at bottom
; Y=0, A=0 after this call
eloop:
ldy #180 ; Y=180 down to 0 STEP 6
yloop:
ldx #4 ; FOR X=4 to 278 STEP 6
xloop:
frame_smc:
lda $D000 ; 3 ; also FRAME
and #1 ; 2
sta HGR_SCALE ; 2
inc HGR_SCALE ; 2 = 9
; ldx #1 ; 2
; ldy FRAME ; 2
; lda $D000,y ; 3
; bmi no_add ; 2
; inx ; 1
;no_add: ;
; stx HGR_SCALE ; 2 = 12
stx XREG ; save X
sty YREG ; save Y
; setup X and Y co-ords
tya ; YPOS into A
ldy #0 ; Y always 0
; XPOS already in X
jsr HPOSN ; X= (y,x) Y=(a)
ldx #<shape_table ; point to our shape
lda #0 ; ROT=0
tay ; ldy #>shape_table
jsr XDRAW0 ; XDRAW 1 AT X,Y
; Both A and X are 0 at exit
jsr RESTORE ; restore FLAGS/X/Y/A
nextx: ; NEXT X
inc frame_smc+1
txa
clc ; 1
adc #6 ; x+=6 ; 2
tax
bne xloop ; if so, loop ; 2
nexty:
; carry always set if we get here
; sec
tya
sbc #6 ; y-=6
tay
bne yloop ; if so, loop
beq eloop
shape_table:
.byte 18,63,36,36,45,45,54,54,63,0 ; data