mirror of
https://github.com/a2-4am/4cade.git
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105 lines
2.0 KiB
Plaintext
105 lines
2.0 KiB
Plaintext
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;license:MIT
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;(c) 2019 by 4am
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;
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; randomized fade-to-black routine customized for a specific piece of cover art
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; with 75 fill rectangles
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;
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; Linear Congruential Pseudo-Random Number Generator
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; (c) 2004 Bruce Clark
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; http://www.6502.org/source/integers/random/random.html
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!cpu 6502
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!to "build/FX/COVERFADE",plain
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*=$6000
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COUNTER = $F7
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SEED = $F8 ; 4 bytes
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TMP = $FC ; 4 bytes
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jsr InitPRNG
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lda #75
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sta COUNTER
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- jsr PRNG
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lda SEED+3
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and #$7F
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cmp #75
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bcs -
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tax
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ldy Order,x
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cpy #$FF
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bne -
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dec COUNTER
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lda COUNTER
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sta Order,x
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bne -
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lda #74
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sta COUNTER
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- lda $C000
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bmi @done
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ldx COUNTER
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ldy Order,x
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lda TransformHi,y
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sta @j+2
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lda TransformLo,y
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sta @j+1
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@j jsr $FDFD ; SMC
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lda #80
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jsr WaitForKeyWithTimeout
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dec COUNTER
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bpl -
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@done rts
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InitPRNG
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lda $4E
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sta SEED
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lda $4F
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sta SEED+1
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lda $c050
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sta SEED+2
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lda $c000
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sta SEED+3
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rts
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RAND7BIT
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rts
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PRNG
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lda #$01
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ldx #$03
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- sta TMP,x
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lsr
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dex
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bpl -
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ldy #$20
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bne @rotateseed ; always branches
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@loop bcc @rotatetmp
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clc
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ldx #$03
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- lda TMP,x
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adc @randtable,x
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sta TMP,x
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dex
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bpl -
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@rotatetmp
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ror TMP
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ror TMP+1
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ror TMP+2
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ror TMP+3
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@rotateseed
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ror SEED+3
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ror SEED+2
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ror SEED+1
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ror SEED
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dey
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bpl @loop
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rts
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@randtable
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!byte $00,$19,$66,$0D
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Order
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!fill 75,$FF
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!source "src/wait.a"
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!source "src/fx/fx.cover.fade.data.a"
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