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base:fpp-last-line

FPP - by repeating the last line

Here follows a code example of FPP by repeating the last line of a char. The advantage of repeating the last line is the possibility of opening the sideborder, and having more time on each line. The drawback is less amount of usable graphic lines, only 8 lines per video-bank.

       *= $0900
        sei

        ldx #0 ; Put some crap data to make empty graphic banks visible
b_1
        lda #$f3
        sta $2000,x
        lda #$28
        sta $2100,x
        lda #$ad
        sta $2800,x
        lda #$99
        sta $2900,x
        lda #$71
        sta $3000,x
        lda #$ed
        sta $3100,x
        lda #$3b
        sta $3800,x
        lda #$cc
        sta $3900,x
        inx
        bne b_1

loop1
        bit $d011 ; Wait for new frame
        bpl *-3
        bit $d011
        bmi *-3

        lda #$1b ; Set y-scroll to normal position
        sta $d011
        lda #$17 ; Set normal d018
        sta $d018

        jsr SetupD018Table ; Nice FPS-effect

        lda #$51 ; Wait for position where we want FPD to start
        cmp $d012
        bne *-3

        ldy #10 ; Wait one more line..
        dey
        bne *-1
        nop
        nop
        cmp $d012 ; ..and make a bit more stabel raster
        bne *+5
        bit 0
        nop

        nop

        ldx #0 ; Clear counter
loop2
        ldy #5 ; Wait some cycles
        dey
        bne *-1
        nop
        nop
        nop
        nop

        ldy D018Table,x
        lda $d012
        and #7
        ora #$18
        sta $d011 ; Do one line of linecrunch
        sty $d018 ; Set graphics bank of next line

        inx
        cpx #100
        beq loop1 ; Exit if end is reached
        jmp loop2 ; Otherwise loop

SetupD018Table
        lda #0 ; First clear the table
        ldy #0
        sta D018Table,y
        iny
        bne *-4

        lda #0 ; Increase the starting value
        inc *-1
        asl
        sta AddVal

        lda #$10 ; Set starting position of stretch-effect
        sta YPos

        ldx #0
        ldy #0 ; This loop will calculate 8 different d018-values into the table..
               ; Each value will be stretched down from the position of the last value
               ; and thus simulate a stretcher effect (FPS).
SDT_1
        lda AddVal
        clc
        adc #10
        sta AddVal
        bpl *+4
        eor #$ff
        lsr
        lsr
        lsr
        lsr
        sec
        adc YPos
        sta YPos
        tya
        asl
SDT_2
        sta D018Table,x
        inx
        cpx YPos
        bcc SDT_2

        iny
        cpy #8
        bcc SDT_1
        rts

YPos    .byte 0
AddVal  .byte 0

        .align $100 ; Align the table to a new page, this way lda D018Table,x always takes 4 cycles.
D018Table
        .dsb 100,0 ; Reserve 100 bytes for the table
base/fpp-last-line.txt · Last modified: 2015-04-17 04:32 (external edit)