;license:MIT
;(c) 2019-2020 by 4am/qkumba
;
; randomized fade-to-black routine customized for a specific piece of cover art
; with 75 fill rectangles
;

!cpu 6502
!to "build/COVERFADE",plain
*=$6000

         !source "src/fx/macros.a"

         +READ_ROM_NO_WRITE

         ;init RNG

         lda   $C050
         and   #$7F
         bne   +
         lda   #$01
+        sta   @rnd+1
         sta   @exit+1

         lda   #$20
         sta   $e6

         ;iterate

@loop    ldy   @rnd+1
         tya
         lsr
         bcc   +

         ;feedback polynomial forms #$41 for period of 127

         eor   #$41
+        sta   @rnd+1
         cpy   #75+1
         bcs   +

         lda   width - 1, y
         sta   $fd
         lda   height - 1, y
         sta   $fe
         lda   startx - 1, y
         sta   $ff
         lda   starty - 1, y

--       pha

         ldx   #0
         ldy   #0
         jsr   $f411   ;hposn

         lda   #0
         ldx   $fd
         ldy   $ff
-        sta   ($26), y
         iny
         dex
         bne   -
         pla
         clc
         adc   #1
         dec   $fe
         bne   --

         lda   #80
         sec
@wait1   pha
@wait2   sbc   #1
         bne   @wait2
         pla
         sbc   #1
         bne   @wait1

+
@rnd     lda   #0
@exit    cmp   #1
         bne   @loop
         +READ_RAM1_WRITE_RAM1
         rts

width
         !byte 02, 03, 03, 05, 03, 03, 03, 03
         !byte 03, 03, 03, 03, 04, 04, 03, 02
         !byte 03, 03, 04, 07, 03, 02, 03, 03
         !byte 03, 03, 03, 03, 03, 03, 03, 03
         !byte 02, 03, 07, 04, 05, 03, 05, 05
         !byte 03, 04, 06, 07, 04, 03, 03, 03
         !byte 03, 02, 04, 05, 03, 03, 04, 06
         !byte 03, 02, 04, 06, 03, 03, 03, 03
         !byte 04, 03, 02, 03, 02, 03, 03, 03
         !byte 03, 03, 02

height
         !byte 12, 16, 26, 13, 15, 09, 24, 18
         !byte 11, 23, 17, 15, 13, 20, 22, 13
         !byte 16, 12, 21, 18, 10, 15, 10, 21
         !byte 17, 12, 12, 12, 17, 12, 08, 26
         !byte 18, 13, 44, 23, 21, 19, 17, 30
         !byte 11, 10, 25, 18, 07, 14, 13, 15
         !byte 11, 12, 28, 16, 15, 17, 35, 17
         !byte 07, 13, 12, 06, 11, 12, 19, 15
         !byte 11, 08, 13, 07, 16, 12, 24, 16
         !byte 23, 22, 11

startx
         !byte 000, 000, 001, 000, 000, 000, 000, 002
         !byte 003, 001, 004, 003, 003, 003, 006, 007
         !byte 005, 006, 006, 007, 008, 009, 008, 009
         !byte 010, 011, 011, 012, 012, 012, 013, 014
         !byte 015, 015, 014, 016, 017, 018, 017, 018
         !byte 020, 020, 021, 021, 022, 022, 024, 025
         !byte 024, 026, 027, 026, 028, 029, 028, 027
         !byte 030, 031, 031, 032, 034, 033, 033, 033
         !byte 032, 033, 034, 035, 036, 037, 037, 037
         !byte 037, 037, 038

starty
         !byte 000, 016, 042, 076, 103, 153, 167, 003
         !byte 027, 123, 049, 098, 152, 172, 008, 036
         !byte 139, 119, 071, 154, 101, 131, 181, 009
         !byte 040, 070, 115, 134, 091, 177, 008, 030
         !byte 068, 109, 128, 169, 003, 031, 058, 091
         !byte 150, 179, 117, 072, 025, 046, 002, 151
         !byte 178, 095, 008, 046, 069, 094, 118, 173
         !byte 040, 018, 058, 003, 015, 034, 079, 106
         !byte 147, 163, 178, 133, 051, 178, 148, 106
         !byte 073, 022, 000