First public commit.

lenser/bbc/viewer/slideshow.s

@@ -0,0 +1,174 @@
+; 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