313 lines
5.0 KiB
ArmAsm
313 lines
5.0 KiB
ArmAsm
; Display falling snow
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; by deater (Vince Weaver) <vince@deater.net>
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; Zero Page
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CH = $24
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CV = $25
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GBASL = $26
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GBASH = $27
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BASL = $28
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BASH = $29
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SEEDL = $4E
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SEEDH = $4F
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HGR_COLOR = $E4
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SNOWX = $F0
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TEMPY = $F1
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HGR = $F3E2
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NUMFLAKES = 10
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.include "hardware.inc"
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;==================================
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;==================================
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jsr HGR
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bit FULLGR
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;==================================
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; init snow
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;==================================
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ldx #NUMFLAKES-1
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snow_init_loop:
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jsr random16
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lda SEEDL
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and #$3f
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sta snow_x,X
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lda SEEDH
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and #$7f
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sta snow_y,X
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dex
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bpl snow_init_loop
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display_loop:
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; 0 4 8 c 10 14 18 1c
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; 0 1 2 3 4 5 6 7
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;=========================
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; erase old snow
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;=========================
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; 2 + (40+38+7)*NUMFLAKES - 1
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; 1 + 85*NUMFLAKES = 851
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ldx #0 ; 2
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erase_loop:
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lda snow_y,X ; get Y ; 4+
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lsr ; 2
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lsr ; 2
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lsr ; divide by 8 ; 2
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sta TEMPY ; 3
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lda snow_x,X ; 4+
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tay ; 2
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lda div_7_q,Y ; 4+
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ldy TEMPY ; 3
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clc ; 2
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adc hgr_offsets_l,Y ; 4+
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sta GBASL ; 3
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adc #30 ; 2
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sta BASL ; 3
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;=============
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; 40
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lda snow_y,X ; 4+
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asl ; 2
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asl ; 2
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and #$1f ; 2
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clc ; 2
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adc hgr_offsets_h,Y ; 4
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sta GBASH ; 3
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sta BASH ; 3
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lda #0 ; 2
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tay ; 2
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sta (GBASL),Y ; 6
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sta (BASL),Y ; 6
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;============
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; 38
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inx ; 2
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cpx #NUMFLAKES ; 2
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bne erase_loop ; 3
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;============
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; 7
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; -1
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;==========================
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; move snow
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;
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; 2 + NUM_FLAKES*(9+17+56+16+11+7) -1
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; 1 + NUM_FLAKES*116 = 1161
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ldx #0 ; 2
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move_snow:
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; Check if off edge of screen
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lda snow_y,X ; 4+
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cmp #160 ; 2
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beq snow_new_y ; 3
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;==========
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; 9
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no_new_y:
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; -1
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lda SEEDH ; 3
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lda SEEDH ; 3
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lda SEEDH ; 3
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lda SEEDH ; 3
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lda SEEDH ; 3
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jmp just_inc ; 3
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;============
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; 17
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snow_new_y:
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; out of bounds, get new
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lda #32 ; 2
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sta snow_y,X ; 5
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lda SEEDH ; 3
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and #$3f ; 2
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sta snow_x,X ; 5
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;============
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; 17
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just_inc:
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jsr random16 ; 6+42
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lda SEEDL ; 3
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and #$f ; 2
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beq snow_left ; 3
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;===============
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; 56
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; if left = 7 = 6 + (9) = 16
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; if right = 4+10 = 13 + (2) = 16
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; else = 4+9 = 12 + (3) = 16
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; -1
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cmp #$1 ; 2
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beq snow_right ; 3
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;===============
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; 4
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snow_else:
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lda SEEDL ; nop ; 3
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; -1
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inc snow_y,X ; 7
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jmp snow_no ; 3
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;===============
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; 8+3
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snow_right:
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nop ; 2
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inc snow_x,X ; 7
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jmp snow_no ; 3
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;============
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; 9+2
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snow_left:
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dec snow_x,X ; 7
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lda SEEDL ; nop
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lda SEEDL ; nop
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lda SEEDL ; nop
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snow_no:
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lda snow_x,X ; 4+
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and #$3f ; 2
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sta snow_x,X ; 5
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;====
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; 11
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done_inc:
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inx ; 2
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cpx #NUMFLAKES ; 2
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bne move_snow ; 3
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;===========
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; 7
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; -1
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;=========================
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; draw new snow
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;=========================
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; 2+ (40+22+28+7)*NUMFLAKES -1
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; 1+97*NUMFLAKES = 971
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ldx #0 ; 2
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draw_loop:
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lda snow_y,X ; 4+
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lsr ; 2
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lsr ; 2
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lsr ; 2
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sta TEMPY ; 3
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lda snow_x,X ; 4+
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tay ; 2
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lda div_7_q,Y ; 4+
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ldy TEMPY ; 3
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clc ; 2
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adc hgr_offsets_l,Y ; 4+
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sta GBASL ; 3
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adc #30 ; 2
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sta BASL ; 3
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;===========
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; 40
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lda snow_y,X ; 4+
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asl ; 2
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asl ; 2
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and #$1f ; 2
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clc ; 2
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adc hgr_offsets_h,Y ; 4+
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sta GBASH ; 3
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sta BASH ; 3
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;=============
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; 22
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ldy snow_x,X ; 4+
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lda div_7_r,Y ; 4+
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tay ; 2
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lda pixel_lookup,Y ; 4+
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ldy #0 ; 2
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sta (GBASL),Y ; 6
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sta (BASL),Y ; 6
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;=============
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; 28
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inx ; 2
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cpx #NUMFLAKES ; 2
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bne draw_loop ; 3
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;=============
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; 7
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; -1
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lda #100
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jsr WAIT
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jmp display_loop ; 3
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snow_x:
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.byte 0,0,0,0,0,0,0,0,0,0
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snow_y:
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.byte 0,0,0,0,0,0,0,0,0,0
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hgr_offsets_h:
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.byte >$2000,>$2080,>$2100,>$2180,>$2200,>$2280,>$2300,>$2380
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.byte >$2028,>$20A8,>$2128,>$21A8,>$2228,>$22A8,>$2328,>$23A8
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.byte >$2050,>$20D0,>$2150,>$21D0,>$2250,>$22D0,>$2350,>$23D0
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hgr_offsets_l:
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.byte <$2000,<$2080,<$2100,<$2180,<$2200,<$2280,<$2300,<$2380
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.byte <$2028,<$20A8,<$2128,<$21A8,<$2228,<$22A8,<$2328,<$23A8
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.byte <$2050,<$20D0,<$2150,<$21D0,<$2250,<$22D0,<$2350,<$23D0
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div_7_q:
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.byte 0,0,0,0,0,0,0 ; 0..6
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.byte 1,1,1,1,1,1,1 ; 7..13
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.byte 2,2,2,2,2,2,2 ; 14..20
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.byte 3,3,3,3,3,3,3 ; 21..27
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.byte 4,4,4,4,4,4,4 ; 28..34
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.byte 5,5,5,5,5,5,5 ; 35..41
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.byte 6,6,6,6,6,6,6 ; 42..48
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.byte 7,7,7,7,7,7,7 ; 49..55
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.byte 8,8,8,8,8,8,8 ; 56..62
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.byte 9 ; 63
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div_7_r:
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.byte 0,1,2,3,4,5,6 ; 0..6
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.byte 0,1,2,3,4,5,6 ; 7..13
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.byte 0,1,2,3,4,5,6 ; 14..20
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.byte 0,1,2,3,4,5,6 ; 21..27
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.byte 0,1,2,3,4,5,6 ; 28..34
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.byte 0,1,2,3,4,5,6 ; 35..41
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.byte 0,1,2,3,4,5,6 ; 42..48
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.byte 0,1,2,3,4,5,6 ; 49..55
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.byte 0,1,2,3,4,5,6 ; 56..62
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.byte 0 ; 63
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pixel_lookup:
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.byte $01,$02,$04,$08,$10,$20,$40
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.include "random16.s"
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