; lenser -- BBC Micro slideshow loader (6502), loaded at PAGE (&1900) and *RUN.
;
; Sets the screen MODE once, then steps through NIMAGES pictures stored as DFS
; files "00".."NN".  For each slide it programmes that image's logical->physical
; palette (from the ss_pal table), *LOADs the file straight into screen memory,
; and waits (key / seconds / both) before advancing.
;
; #defines from the build wrapper --
;   WAITMODE 1 key / 2 seconds / 3 both    WAITSECS timeout    RATE 50/60 fps
;   NIMAGES image count   LOOPFLAG 1 wrap / 0 stop   MODE screen mode   NCOL colours
; The packager patches the screen-base hex into the OSCLI string and appends the
; ss_pal table (NCOL physical-colour bytes per image).

OSWRCH = $FFEE
OSRDCH = $FFE0
OSBYTE = $FFF4
OSCLI  = $FFF7

palptr = $70
cnt    = $72

        * = $1900
start:
        ; ---- VDU 22, mode (once) ----
        lda #22
        jsr OSWRCH
        lda #MODE
        jsr OSWRCH

        ; ---- hide the text cursor (VDU 23,1,0;0;0;0;) ----
        lda #23
        jsr OSWRCH
        lda #1
        jsr OSWRCH
        ldx #8
curz:
        lda #0
        jsr OSWRCH
        dex
        bne curz

        lda #0
        sta ssidx

ssmain:
        ; ---- palptr = ss_pal + ssidx*NCOL ----
        lda #<ss_pal
        sta palptr
        lda #>ss_pal
        sta palptr+1
        ldx ssidx
        beq setpal
pmul:
        clc
        lda palptr
        adc #NCOL
        sta palptr
        bcc pm1
        inc palptr+1
pm1:
        dex
        bne pmul
setpal:
        ; ---- VDU 19, logical, physical, 0,0,0  for each logical colour ----
        ldx #0
pl:
        cpx #NCOL
        beq pldone
        lda #19
        jsr OSWRCH
        txa
        jsr OSWRCH                ; logical colour = X
        txa
        tay
        lda (palptr),y
        jsr OSWRCH                ; physical colour
        lda #0
        jsr OSWRCH
        jsr OSWRCH
        jsr OSWRCH
        inx
        bne pl
pldone:

        ; ---- build the filename digits "NN" into the OSCLI string ----
        lda ssidx
        ldx #$2f
        sec
nten:
        inx
        sbc #10
        bcs nten
        adc #10
        ora #$30
        sta cmd+6                 ; ones digit
        txa
        sta cmd+5                 ; tens digit

        ; ---- *LOAD NN <base> straight into screen memory ----
        ldx #<cmd
        ldy #>cmd
        jsr OSCLI

        jsr sswait

        inc ssidx
        lda ssidx
        cmp #NIMAGES
        bcc ssmain
#if LOOPFLAG == 1
        lda #0
        sta ssidx
        jmp ssmain
#else
        rts                       ; back to BASIC
#endif

; ---- wait (returns), flushing the keyboard buffer first ----
sswait:
        lda #15
        ldx #1
        jsr OSBYTE                ; flush input buffers
#if WAITMODE == 1
        jsr OSRDCH                ; block until a key
        rts
#endif
#if WAITMODE == 2
        lda #<(WAITSECS*RATE)
        sta cnt
        lda #>(WAITSECS*RATE)
        sta cnt+1
sw2:
        lda #19
        jsr OSBYTE                ; wait for vertical sync (1 frame)
        lda cnt
        bne sd2
        dec cnt+1
sd2:
        dec cnt
        lda cnt
        ora cnt+1
        bne sw2
        rts
#endif
#if WAITMODE == 3
        lda #<(WAITSECS*RATE)
        sta cnt
        lda #>(WAITSECS*RATE)
        sta cnt+1
sw3:
        lda #129
        ldx #0
        ldy #0
        jsr OSBYTE                ; INKEY(0) -- poll keyboard, no wait
        cpy #$ff
        bne sw3d                  ; Y != $FF -> a key was pressed
        lda #19
        jsr OSBYTE                ; wait one frame
        lda cnt
        bne sd3
        dec cnt+1
sd3:
        dec cnt
        lda cnt
        ora cnt+1
        bne sw3
sw3d:
        rts
#endif

ssidx:  .byte 0
; OSCLI string -- packager patches the 4-hex screen base; loader patches "NN"
cmd:    .byte "LOAD 00 0000", 13
; ss_pal table (NCOL bytes per image) appended by the build wrapper