mirror of
https://github.com/deater/dos33fsprogs.git
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238 lines
3.7 KiB
ArmAsm
238 lines
3.7 KiB
ArmAsm
; water drops
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; based roughly on
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; https://github.com/seban-slt/Atari8BitBot/blob/master/ASM/water/water.m65
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; for each pixel
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; C
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; A V B
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; D
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;
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; calculate color as NEW_V = (A+B+C+D)/2 - OLD_V
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; then flip buffers
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; 211 bytes -- initial
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; 208 bytes -- use HGR2 to clear
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; 204 bytes -- optimize buffer switch
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; 197 bytes -- inline random8
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; 169 bytes -- rip out page flipping
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; 163 bytes -- use EOR for BUFH setting
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; 159 bytes -- put YY in X
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; 153 bytes -- fake random by reading ROM
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; 151 bytes -- no seed at all, use frame
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; 149 bytes -- FRAME saved in Y
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; 148 bytes -- beq instead of jmp
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; 147 bytes -- reuse color in drop
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; 145 bytes -- leave out carry setting
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; 142 bytes -- reduce to 4 colors (from 8)
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; 141 bytes -- don't dex at beginning ($FF close enough)
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.include "hardware.inc"
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GBASH = $27
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MASK = $2E
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COLOR = $30
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SEEDL = $4E
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FRAME = $F8
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XX = $F9
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DROPL = $FA
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DROPH = $FB
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BUF1L = $FC
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BUF1H = $FD
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BUF2L = $FE
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BUF2H = $FF
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;================================
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; Clear screen and setup graphics
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;================================
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drops:
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jsr HGR ; clear $2000-$4000 to zero
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; A is $00 after this
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; Y is $00
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bit FULLGR ; full page
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bit LORES ; switch to LORES
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drops_outer:
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; in all but first loop X is $FF on arrival
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; inx
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stx BUF1L
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stx BUF2L
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;=================================
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; handle new frame
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;=================================
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inc FRAME
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lda FRAME
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tay ; save frame for later
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; alternate $20/$28 in BUF1H/BUF2H
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and #$1
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asl
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asl
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asl ; A now 0 or 8
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ora #$20
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sta BUF1H
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eor #$8
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sta BUF2H
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; check if we add new raindrop
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tya ; reload FRAME
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and #$3 ; only drop every 4 frames
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bne no_drop
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; fake random number generator by reading ROM
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lda $E000,Y
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; buffer is 40x48 = roughly 2k?
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; so random top bits = 0..7
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sta DROPL
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and #$7
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ora #$20
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sta DROPH
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lda #31 ; $1f value for drop
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tay ; cheat and draw drop at offset 31 to reuse value
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sta (DROPL),Y ; draw at offset 31
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iny
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sta (DROPL),Y ; draw at offset 32
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ldy #71
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sta (DROPL),Y ; draw at offset 71 (y+1)
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iny
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sta (DROPL),Y ; draw at offset 72
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no_drop:
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ldx #47 ; load 47 into YY
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;=================================
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; yloop
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;=================================
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drops_yloop:
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txa ; YY
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tay ; plot YY,YY
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jsr PLOT ; PLOT Y,A, setting up MASK and putting addr in GBASL/H
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; reset XX to 39
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lda #39 ; XX
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sta XX
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;=================================
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; xloop
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;=================================
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drops_xloop:
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clc
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ldy #1
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lda (BUF1L),Y
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ldy #81
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adc (BUF1L),Y
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ldy #40
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adc (BUF1L),Y
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ldy #42
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adc (BUF1L),Y
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lsr
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dey
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; sec
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sbc (BUF2L),Y
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bpl done_calc
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eor #$ff
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done_calc:
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sta (BUF2L),Y
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inc BUF1L
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inc BUF2L
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bne no_oflo
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inc BUF1H
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inc BUF2H
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no_oflo:
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; adjust color
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lsr
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lsr
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and #$3
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tay
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lda colors,Y
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sta COLOR
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ldy XX
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jsr PLOT1 ; PLOT AT (GBASL),Y
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dec XX
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bpl drops_xloop
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dex ; YY
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bpl drops_yloop
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weird_outer:
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bmi drops_outer ; small enough now!
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colors:
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.byte $22,$66,$77,$ff
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;colors:
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;.byte $00,$22,$66,$EE,$77,$ff,$ff,$ff
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; 0 2 6 e 7 f f f
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; 0000 0010 0110 1110 0111 1111 1111 1111
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; 0 1 2 3 4 5 6 7
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; for maximum twitter size we enter this program
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; by using the "&" operator which jumps to $3F5
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; we can't load there though as the code would end up overlapping
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; $400 which is the graphics area
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; this is at 38A
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; we want to be at 3F5, so load program at 36B?
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; called by EXECUTE.STATEMENT at $D828
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; which jumps to CHRGET at $00B1
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; which does a RTS to $3F4 at end
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; CHRGET sets up state based on the char that follows the &
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; Z==C==1 is colon
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; Z==1 is EOL (nul)
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; C==0 is digit
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; when we call with " following
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; A=$22 (") X=$FF Y=$5E
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; N=0 V=0 Z=0 C=1
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jmp drops ; entry point from &
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; bcs drops
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