mist: can actually take the tower elevator

mist/leveldata_octagon.inc

@@ -351,8 +351,10 @@ location18:
 	.word	$0000			; east bg
 	.word	$0000			; west bg
 	.byte	BG_SOUTH
-	.byte	$ff
-
+	.byte	DIRECTION_S	; special exit
+	.byte	29,35		; special x
+	.byte	34,40		; special y
+	.word	elevator_button-1	; special function
 
 ; OCTAGON_TOWER_BOOK		-- tower, bookside
 location19:
@@ -390,12 +392,12 @@ location20:
 
 ; OCTAGON_BOOK_VIEW		-- ladder, view outside
 location21:
-	.byte	$ff			; north exit
-	.byte	OCTAGON_BOOK_LADDER	; south exit
+	.byte	OCTAGON_BOOK_LADDER	; north exit
+	.byte	$ff			; south exit
 	.byte	$ff			; east exit
 	.byte	$ff			; west exit
-	.byte	$ff		; north exit_dir
-	.byte	DIRECTION_S	; south exit_dir
+	.byte	DIRECTION_N	; north exit_dir
+	.byte	$ff		; south exit_dir
 	.byte	$ff		; east exit_dir
 	.byte	$ff		; west exit_dir
 	.word	tower_book_view_n_lzsa		; north bg

mist/octagon_bookshelf.s

@@ -1,4 +1,49 @@
 
+	; elevator button pressed
+
+elevator_button:
+
+	; see which floor we are on
+
+	ldy	#LOCATION_SOUTH_EXIT
+	lda	location18,Y
+	cmp	#OCTAGON_ELEVATOR_OUT
+	bne	elevator_goto_library_level
+
+elevator_goto_tower_level:
+	; we want to go up the tower
+
+	; change exit
+	lda	#OCTAGON_TOWER_BOOK
+	sta	location18,Y
+
+	; change bg image
+
+	ldy	#LOCATION_SOUTH_BG
+	lda	#<elevator_tower_s_lzsa
+	sta	location18,Y
+	lda	#>elevator_tower_s_lzsa
+	sta	location18+1,Y
+
+	jmp	change_location
+
+elevator_goto_library_level:
+	; we want to move back to the library
+
+	; change exit
+	lda	#OCTAGON_ELEVATOR_OUT
+	sta	location18,Y
+
+	; change south bg image
+	ldy	#LOCATION_SOUTH_BG
+	lda	#<elevator_lib_s_lzsa
+	sta	location18,Y
+	lda	#>elevator_lib_s_lzsa
+	sta	location18+1,Y
+
+	jmp	change_location
+
+
 open_bookshelf:
 
 	; change background of center room N