dos33fsprogs/textmode/textscroll/comet.s
2021-04-21 01:14:58 -04:00

165 lines
2.4 KiB
ArmAsm

CH = $24
CV = $25
BASL = $28
BASH = $29
SEEDL = $4E
FACL = $9D
FACH = $9E
DRAW_PAGE = $FF
PAGE0 = $C054
GETCHAR = $D72C
HGR = $F3E2
SETTXT = $FB39
TABV = $FB5B ; store A in CV and call MON_VTAB
STORADV = $FBF0 ; store A at (BASL),CH, advancing CH, trash Y
MON_VTAB = $FC22 ; VTAB to CV
VTABZ = $FC24 ; VTAB to value in A
HOME = $FC58
WAIT = $FCA8 ;; delay 1/2(26+27A+5A^2) us
COUT = $FDED
COUT1 = $FDF0
COUTZ = $FDF6 ; cout but ignore inverse flag
ypos = $2000
xpos = $2100
textl = $2200
texth = $2300
move:
jsr HGR
sta DRAW_PAGE
jsr SETTXT
next_frame:
ldx #0
next_text:
lda xpos,X
bne not_new
new_text:
jsr random8
and #$1f
adc #$4
sta xpos,X
jsr random8
and #$f
sta ypos,X
lda #<text
sta textl,X
lda #>text
sta texth,X
not_new:
lda xpos,X
sta CH
lda ypos,X
sta CV
jsr MON_VTAB
lda BASH
clc
adc DRAW_PAGE
sta BASH
ldy #0
lda textl,X
sta FACL
lda texth,X
sta FACH
txa
pha
print_loop:
jsr GETCHAR
php
ora #$80
jsr STORADV
plp
bpl print_loop
big_done:
pla
tax
dec xpos,X
inx
cpx #20
bne next_text
flip_pages:
ldx #0
lda 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
clc
adc #$4
sta BASH
lda #$0
sta BASL
clear_screen_outer:
ldy #$f8
clear_screen_inner:
lda #$A0 ; space char
sta (BASL),Y ; 100 101 110 111
dey
cpy #$FF
bne clear_screen_inner
inc BASH
lda BASH
and #$3
bne clear_screen_outer
lda #$50
jsr WAIT
jmp next_frame
;=============================
; 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
rts
text:
.byte "HELL",'O'|$80