; lenser -- BBC Micro viewer (6502), loaded at PAGE (&1900) and *RUN.
;
; Sets the screen MODE, programmes the logical->physical palette, then *LOADs the
; image file "IMG" straight into screen memory, and holds it per the display
; option.  Parameters come from a fixed block the packager fills in (so the code
; is constant); see build_viewer() in assemble.py.
;
; #defines from the wrapper -- WAITMODE (0 forever, 1 key, 2 seconds), WAITSECS, RATE.
;
; assembled by bbc/viewer/assemble.py via xa

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

        * = $1900
start:
        ; ---- VDU 22, mode ----
        lda #22
        jsr OSWRCH
        lda p_mode
        jsr OSWRCH

        ; ---- palette via VDU 19, logical, physical, 0,0,0  for each logical ----
        ldx #0
palloop:
        cpx p_ncol
        beq paldone
        lda #19
        jsr OSWRCH
        txa
        jsr OSWRCH                ; logical colour = X
        lda p_pal,x
        jsr OSWRCH                ; physical
        lda #0
        jsr OSWRCH
        jsr OSWRCH
        jsr OSWRCH
        inx
        bne palloop
paldone:

        ; ---- 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

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

        ; ---- hold the picture ----
#if WAITMODE == 0
hang:
        jmp hang
#endif
#if WAITMODE == 1
        jsr OSRDCH                ; block until a key
        rts                       ; back to BASIC
#endif
#if WAITMODE == 2
        lda #<(WAITSECS*RATE)
        sta cnt
        lda #>(WAITSECS*RATE)
        sta cnt+1
swait:
        lda #19
        jsr OSBYTE                ; OSBYTE 19 = wait for vertical sync
        lda cnt
        bne sdec
        dec cnt+1
sdec:
        dec cnt
        lda cnt
        ora cnt+1
        bne swait
        rts                       ; back to BASIC
#endif

cnt:    .byte 0,0

; OSCLI string -- the packager patches in the right screen-base hex
cmd:    .byte "LOAD IMG ", "0000", 13

; parameter block -- the packager fills these in
p_mode: .byte 0
p_ncol: .byte 0
p_pal:  .byte 0,0,0,0,0,0,0,0