dos33fsprogs/streams/snow.s

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; Display falling snow
; by deater (Vince Weaver) <vince@deater.net>
; Zero Page
CH = $24
CV = $25
GBASL = $26
GBASH = $27
BASL = $28
BASH = $29
SEEDL = $4E
SEEDH = $4F
HGR_COLOR = $E4
SNOWX = $F0
TEMPY = $F1
HGR = $F3E2
NUMFLAKES = 10
.include "hardware.inc"
;==================================
;==================================
jsr HGR
bit FULLGR
;==================================
; init snow
;==================================
ldx #NUMFLAKES-1
snow_init_loop:
jsr random16
lda SEEDL
and #$3f
sta snow_x,X
lda SEEDH
and #$7f
sta snow_y,X
dex
bpl snow_init_loop
display_loop:
; 0 4 8 c 10 14 18 1c
; 0 1 2 3 4 5 6 7
;=========================
; erase old snow
;=========================
; 2 + (35+29+7)*NUMFLAKES - 1
; 1 +71*NUMFLAKES = 711
ldx #0 ; 2
erase_loop:
lda snow_y,X ; get Y ; 4+
lsr ; 2
lsr ; 2
lsr ; divide by 8 ; 2
sta TEMPY ; 3
lda snow_x,X ; 4+
tay ; 2
lda div_7_q,Y ; 4+
ldy TEMPY ; 3
clc ; 2
adc hgr_offsets_l,Y ; 4+
sta GBASL ; 3
adc #30
sta BASL
;=============
; 35
lda snow_y,X ; 4+
asl ; 2
asl ; 2
and #$1f ; 2
clc ; 2
adc hgr_offsets_h,Y ; 4
sta GBASH ; 3
sta BASH
lda #0 ; 2
tay ; 2
sta (GBASL),Y ; 6
sta (BASL),Y
;============
; 29
inx ; 2
cpx #NUMFLAKES ; 2
bne erase_loop ; 3
;============
; 7
; -1
;==========================
; move snow
;
; 2 +
ldx #0 ; 2
move_snow:
lda snow_y,X ; 4+
cmp #160 ; 2
bne just_inc ; 3
; -1
; out of bounds, get new
lda #30 ; 2
sta snow_y,X ; 5
lda SEEDH
and #$3f
sta snow_x,X
jmp done_inc ; 3
just_inc:
jsr random16 ; 6+42
lda SEEDL ; 3
and #$f ; 2
beq snow_left ; 3
; -1
cmp #$1 ; 2
beq snow_right ; 3
; -1
inc snow_y,X ; 6
jmp snow_no ; 3
snow_right:
inc snow_x,X ; 6
jmp snow_no ; 3
snow_left:
dec snow_x,X ; 6
snow_no:
lda snow_x,X
and #$3f
sta snow_x,X
done_inc:
inx ; 2
cpx #NUMFLAKES ; 2
bne move_snow ; 3
; -1
;=========================
; draw new snow
;=========================
; 2+ (35+22+19+7)*NUMFLAKES -1
; 1+83*NUMFLAKES = 831
ldx #0 ; 2
draw_loop:
lda snow_y,X ; 4+
lsr ; 2
lsr ; 2
lsr ; 2
sta TEMPY ; 3
lda snow_x,X ; 4+
tay ; 2
lda div_7_q,Y ; 4+
ldy TEMPY ; 3
clc ; 2
adc hgr_offsets_l,Y ; 4+
sta GBASL ; 3
adc #32
sta BASL
;===========
; 35
lda snow_y,X ; 4+
asl ; 2
asl ; 2
and #$1f ; 2
clc ; 2
adc hgr_offsets_h,Y ; 4+
sta GBASH ; 3
sta BASH
;=============
; 19
ldy snow_x,X ; 4+
lda div_7_r,Y ; 4+
tay ; 2
lda pixel_lookup,Y ; 4+
ldy #0 ; 2
sta (GBASL),Y ; 6
sta (BASL),Y
;=============
; 22
inx ; 2
cpx #NUMFLAKES ; 2
bne draw_loop ; 3
;=============
; 7
; -1
lda #100
jsr WAIT
jmp display_loop ; 3
snow_x:
.byte 0,0,0,0,0,0,0,0,0,0
snow_y:
.byte 0,0,0,0,0,0,0,0,0,0
hgr_offsets_h:
.byte >$2000,>$2080,>$2100,>$2180,>$2200,>$2280,>$2300,>$2380
.byte >$2028,>$20A8,>$2128,>$21A8,>$2228,>$22A8,>$2328,>$23A8
.byte >$2050,>$20D0,>$2150,>$21D0,>$2250,>$22D0,>$2350,>$23D0
hgr_offsets_l:
.byte <$2000,<$2080,<$2100,<$2180,<$2200,<$2280,<$2300,<$2380
.byte <$2028,<$20A8,<$2128,<$21A8,<$2228,<$22A8,<$2328,<$23A8
.byte <$2050,<$20D0,<$2150,<$21D0,<$2250,<$22D0,<$2350,<$23D0
div_7_q:
.byte 0,0,0,0,0,0,0 ; 0..6
.byte 1,1,1,1,1,1,1 ; 7..13
.byte 2,2,2,2,2,2,2 ; 14..20
.byte 3,3,3,3,3,3,3 ; 21..27
.byte 4,4,4,4,4,4,4 ; 28..34
.byte 5,5,5,5,5,5,5 ; 35..41
.byte 6,6,6,6,6,6,6 ; 42..48
.byte 7,7,7,7,7,7,7 ; 49..55
.byte 8,8,8,8,8,8,8 ; 56..62
.byte 9 ; 63
div_7_r:
.byte 0,1,2,3,4,5,6 ; 0..6
.byte 0,1,2,3,4,5,6 ; 7..13
.byte 0,1,2,3,4,5,6 ; 14..20
.byte 0,1,2,3,4,5,6 ; 21..27
.byte 0,1,2,3,4,5,6 ; 28..34
.byte 0,1,2,3,4,5,6 ; 35..41
.byte 0,1,2,3,4,5,6 ; 42..48
.byte 0,1,2,3,4,5,6 ; 49..55
.byte 0,1,2,3,4,5,6 ; 56..62
.byte 0 ; 63
pixel_lookup:
.byte $01,$02,$04,$08,$10,$20,$40
.include "random16.s"