SixtyPical/eg/demo.60p

assign byte[256] screen $0400
assign byte[256] screen2 1274
assign byte[256] screen3 1524
assign byte[256] screen4 1774

assign byte[256] colormap 55296
assign byte[256] colormap2 55546
assign byte[256] colormap3 55796
assign byte[256] colormap4 56046

assign byte vic_border 53280
assign byte[4] vic_bg 53281

assign vector cinv 788
reserve vector save_cinv

assign word position $fb

reserve byte value

reserve word m
reserve word n

routine reset_position {
    lda #$00
    sta <position
    lda #$04
    sta >position
}

routine increment_pos {
    clc
    lda <position
    adc #1
    sta <position
    lda >position
    adc #0
    sta >position
}

routine compare_16_bit {
    lda >m
    cmp >n
    if beq {
        lda <m
        cmp <n
    } else {
    }
}

routine compare_pos {
    lda <position
    sta <m
    lda >position
    sta >m
    lda #$07
    sta >n
    lda #$e8
    sta <n
    jsr compare_16_bit
}

routine clear_screen {
    ldy #0
    repeat bne {
        lda #1
        sta colormap, y
        sta colormap2, y
        sta colormap3, y
        sta colormap4, y
        
        lda #32
        sta screen, y
        sta screen2, y
        sta screen3, y
        sta screen4, y

        iny
        cpy #250
    }
}

routine our_cinv {
    inc value
    lda value
    ldy #0
    sta (position), y
    jsr increment_pos
    jsr compare_pos
    if beq {
        jsr reset_position
    } else {
    }
    jmp (save_cinv)
}

routine main {
    lda #5
    sta vic_border
    lda #0
    sta vic_bg
    jsr reset_position
    jsr clear_screen
    with sei {
        copy cinv save_cinv
        copy routine our_cinv to cinv
    }
    clc
    repeat bcc { }
}