// -------------------------------------
// 1x1 SCROLL SIDE-FLOODER
// Idea by someone from STARION
//
// Done (quite easy) by Digger
// of PETLICZEK DEZIGNS on 1996.09.18
// -------------------------------------

.var vtxt     = $c0//c1
.var cadd     = $c2//c3

.var charline = 24       //pos (0-24)

.var raster   = <$32 + charline * 8
.var scrline  = $0400 + [raster - $32] / 8 * 40

// -------------------------------------

:BasicUpstart2(run)

.pc = $0a00               //sys 2560

run:     lda #$0c
         jsr $e536
         sei
         lda #<irq
         ldy #>irq
         sta $0314
         sty $0315
         lda #<scrtxt
         ldy #>scrtxt
         sta vtxt
         sty vtxt+1
         lda #$7f
         sta $dc0d
         lda #$01
         sta $d01a
         lda #$00
         sta $d021
         sta $d012
         lda #$1b
         sta $d011
         lda #$18
         sta $d018
         cli
         jmp *

// -------------------------------------

irq:     inc $d019

         ldy #0          //right border
         sty cadd+1
         lda scrline
         jsr afont
lp2r:    lda (cadd),y
         ldx roll
         beq passr
lp1r:    ror
         dex
         bpl lp1r
passr:   and #1
         tax
         lda rctab,x
         sta rtab,y
         iny
         cpy #$08
         bne lp2r

         ldy #0          //left border
         sty cadd+1
         lda scrline+$26
         jsr afont
lp2l:    lda (cadd),y
         ldx roll
         beq passl
lp1l:    ror
         dex
         bpl lp1l
passl:   and #1
         tax
         lda lctab,x
         sta ltab,y
         iny
         cpy #$08
         bne lp2l

         lda #raster     //position
         cmp $d012
         bne *-3
         ldx #$0d
         dex
         bne *-1
         lda roll
         sta $d016

// -------------------------------------

         ldy #0          //flooder
lp:      lda rtab+1,y    //split
         sta $d020       //display
         ldx #$03
         dex
         bne *-1
         bit $00
         lda ltab+1,y
         sta $d020
         ldx #$04
         dex
         bne *-1
         iny
         cpy #$07
         bne lp

         lda #0
         sta $d020
         lda #$08
         sta $d016

         lda flg
         beq scroll

         lda speed
         eor #$01
         sta speed

// -------------------------------------
// Ordinary scroll...
// (he, he - beat me it is probably the shortest variable speed 1x1 scroll routine in the world)

scroll:  lda roll
         sec
         sbc speed
         bpl nzero
         and #$07
         sta roll

         ldy #0
rewrite: lda scrline+1,y
         sta scrline,y
         iny
         cpy #$27
         bne rewrite

         ldy #0
         lda (vtxt),y
         bne enter

         lda #<scrtxt
         ldy #>scrtxt
         sta vtxt
         sty vtxt+1
         lda roll
nzero:   sta roll
         jmp end

enter:   sta scrline+$27
         inc vtxt
         bne *+4
         inc vtxt+1
         jmp end

// -------------------------------------
flg:     brk

rtab:    .byte 0,0,0,0,0,0,0,0
ltab:    .byte 0,0,0,0,0,0,0,0

lctab:   .byte 0,$0c    //color
rctab:   .byte 0,$0c

roll:    .byte $07
speed:   .byte 2           // speed (0-8)

// -------------------------------------

afont:   asl               //find char address
         rol cadd+1
         asl
         rol cadd+1
         asl
         rol cadd+1
         sta cadd
         lda cadd+1
         clc
         adc #>charset
         sta cadd+1
         rts

end:     lda $dc01
         cmp #$7f
         beq slow
         cmp #$df
         beq fast
         jmp quit

slow:    lda #1
         sta flg
         sta speed
         jmp quit

fast:    lda #0
         sta flg
         lda #2
         sta speed
         jmp quit

quit:    inc $d019
         jmp $ea81

.pc = $0d00 "Scroll Text"
scrtxt:  .import c64 "scr_text.dat"

.pc = $2000 "Font"
charset: .import c64 "1x1chars.fnt"