mirror of
https://github.com/deater/dos33fsprogs.git
synced 2024-11-01 01:06:33 +00:00
245 lines
3.5 KiB
ArmAsm
245 lines
3.5 KiB
ArmAsm
; water drops
|
|
|
|
; based roughly on
|
|
; https://github.com/seban-slt/Atari8BitBot/blob/master/ASM/water/water.m65
|
|
|
|
; for each pixel
|
|
|
|
; C
|
|
; A V B
|
|
; D
|
|
;
|
|
; calculate color as NEW_V = (A+B+C+D)/2 - OLD_V
|
|
; then flip buffers
|
|
|
|
|
|
; 211 bytes -- initial
|
|
; 208 bytes -- use HGR2 to clear
|
|
; 204 bytes -- optimize buffer switch
|
|
; 197 bytes -- inline random8
|
|
|
|
.include "hardware.inc"
|
|
|
|
GBASH = $27
|
|
MASK = $2E
|
|
COLOR = $30
|
|
SEEDL = $4E
|
|
|
|
FRAME = $F9
|
|
XX = $FA
|
|
YY = $FB
|
|
BUF1L = $FC
|
|
BUF1H = $FD
|
|
BUF2L = $FE
|
|
BUF2H = $FF
|
|
|
|
|
|
;================================
|
|
; Clear screen and setup graphics
|
|
;================================
|
|
drops:
|
|
jsr HGR2 ; clear $4000-$6000 to zero, full page
|
|
bit LORES ; switch to LORES
|
|
|
|
drops_outer:
|
|
|
|
;=================================
|
|
; handle new frame
|
|
;=================================
|
|
|
|
inc FRAME
|
|
|
|
lda FRAME
|
|
and #$f
|
|
bne no_drop
|
|
|
|
; inline random8
|
|
|
|
;=============================
|
|
; 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
|
|
|
|
; buffer is 40x48 = roughly 2k?
|
|
; so random top bits = 0..7
|
|
|
|
sta BUF1L
|
|
and #$7
|
|
clc
|
|
adc #$40
|
|
sta BUF1H
|
|
|
|
lda #$1f
|
|
|
|
ldy #41
|
|
sta (BUF1L),Y
|
|
iny
|
|
sta (BUF1L),Y
|
|
ldy #81
|
|
sta (BUF1L),Y
|
|
iny
|
|
sta (BUF1L),Y
|
|
|
|
no_drop:
|
|
|
|
|
|
lda FRAME
|
|
and #$1
|
|
beq even_frame
|
|
|
|
odd_frame:
|
|
ldy #$40
|
|
lda #$48
|
|
bne done_frame
|
|
even_frame:
|
|
ldy #$48
|
|
lda #$40
|
|
done_frame:
|
|
sty BUF1H
|
|
sta BUF2H
|
|
|
|
lda #$00
|
|
sta BUF1L
|
|
sta BUF2L
|
|
|
|
lda #47
|
|
sta YY
|
|
|
|
|
|
;=================================
|
|
; yloop
|
|
;=================================
|
|
|
|
drops_yloop:
|
|
|
|
lda YY ; plot call needs Y/2
|
|
lsr
|
|
|
|
bcc even_mask
|
|
ldy #$f0
|
|
.byte $C2 ; bit hack
|
|
even_mask:
|
|
ldy #$0f
|
|
sty MASK
|
|
|
|
jsr GBASCALC ; take Y-coord/2 in A, put address in GBASL/H ( a trashed, C clear)
|
|
|
|
lda GBASH
|
|
|
|
draw_page_smc:
|
|
adc #0
|
|
sta GBASH ; adjust for PAGE1/PAGE2 ($400/$800)
|
|
|
|
|
|
; reset XX to 0
|
|
|
|
lda #39 ; XX
|
|
sta XX
|
|
|
|
|
|
;=================================
|
|
; xloop
|
|
;=================================
|
|
|
|
drops_xloop:
|
|
|
|
clc
|
|
ldy #1
|
|
lda (BUF1L),Y
|
|
ldy #81
|
|
adc (BUF1L),Y
|
|
ldy #40
|
|
adc (BUF1L),Y
|
|
ldy #42
|
|
adc (BUF1L),Y
|
|
lsr
|
|
dey
|
|
sec
|
|
sbc (BUF2L),Y
|
|
bpl done_calc
|
|
eor #$ff
|
|
done_calc:
|
|
sta (BUF2L),Y
|
|
|
|
inc BUF1L
|
|
inc BUF2L
|
|
bne no_oflo
|
|
|
|
inc BUF1H
|
|
inc BUF2H
|
|
|
|
no_oflo:
|
|
|
|
; adjust color
|
|
|
|
lsr
|
|
and #$7
|
|
tay
|
|
lda colors,Y
|
|
sta COLOR
|
|
|
|
ldy XX
|
|
jsr PLOT1 ; PLOT AT (GBASL),Y
|
|
|
|
dec XX
|
|
bpl drops_xloop
|
|
|
|
dec YY
|
|
bpl drops_yloop
|
|
|
|
|
|
|
|
flip_pages:
|
|
ldx #0
|
|
|
|
lda draw_page_smc+1 ; DRAW_PAGE
|
|
beq done_page
|
|
inx
|
|
done_page:
|
|
ldy PAGE0,X ; set display page to PAGE1 or PAGE2
|
|
|
|
eor #$4 ; flip draw page between $400/$800
|
|
sta draw_page_smc+1 ; DRAW_PAGE
|
|
|
|
jmp drops_outer ; just slightly too far???
|
|
|
|
|
|
|
|
colors:
|
|
.byte $00,$22,$66,$EE,$77,$FF,$FF,$FF
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
; for maximum twitter size we enter this program
|
|
; by using the "&" operator which jumps to $3F5
|
|
|
|
; we can't load there though as the code would end up overlapping
|
|
; $400 which is the graphics area
|
|
|
|
; this is at 389
|
|
; we want to be at 3F5, so load program at 36C?
|
|
|
|
jmp drops ; entry point from &
|
|
|
|
|
|
|
|
|
|
|