[Maintenance] Clean up the confusion between "tiles" and .STD tile sections

Funded by -Tom-.

th04/formats/std.asm

@@ -28,8 +28,8 @@ std_load	proc near
 	call	file_read pascal, es, si, [bp+@@std_size]
 	call	file_close
 	mov	es, _std_seg
-	mov	_tile_index, 4
-	mov	_tile_row, 0
+	mov	_tile_section, 4
+	mov	_tile_row_in_section, 0
 	mov	al, [bp+@@chunk_size]
 	mov	ah, 0
 	add	si, ax

th04/tiles[bss].asm

@@ -1,6 +1,3 @@
-; Each tile defines a 384×80 section of the background, which internally are
-; further divided into 5 rows of 16 pixels each.
-
 ; No idea why ZUN just didn't go with the actually visible space of 384
 ; horizontal tiles. That's 8 wasted tiles per row that the game doesn't do
 ; anything with?
@@ -18,15 +15,16 @@ _halftiles_dirty_end	label byte
 public _tile_ring
 _tile_ring	dw (TILES_MEMORY_X * TILES_Y) dup(?)
 
+; .STD files reference 384×80 (25×5) sections of tiles.
 if GAME eq 5
-public _tile_index_ptr
-_tile_index_ptr	dw ?
+public _tile_section_ptr
+_tile_section_ptr	dw ?
 else
-public _tile_index
-_tile_index    	dw ?
+public _tile_section
+_tile_section    	dw ?
 endif
 
-public _tile_row, _tile_scrollspeed_ptr
-_tile_row	db ?
+public _tile_row_in_section, _tile_scrollspeed_ptr
+_tile_row_in_section	db ?
          	db ?
 _tile_scrollspeed_ptr	dw ?

th04_main.asm

@@ -1503,10 +1503,10 @@ loc_B84B:
 		mov	word_25100, ax
 		mov	bx, _std_seg
 		mov	es, bx
-		dec	_tile_row
+		dec	_tile_row_in_section
 		jns	short loc_B89D
-		mov	_tile_row, 4
-		inc	_tile_index
+		mov	_tile_row_in_section, 4
+		inc	_tile_section
 		inc	_tile_scrollspeed_ptr
 		mov	bx, _tile_scrollspeed_ptr
 		mov	dl, es:[bx]
@@ -1526,9 +1526,9 @@ loc_B89D:
 		add	ax, offset _tile_ring
 		mov	di, ax
 		xor	ax, ax
-		mov	al, _tile_row
+		mov	al, _tile_row_in_section
 		shl	ax, 6
-		mov	bx, _tile_index
+		mov	bx, _tile_section
 		mov	bl, es:[bx]
 		xor	bh, bh
 		add	bl, bl

th05/formats/std.asm

@@ -55,8 +55,8 @@ std_load	proc near
 	mov	word ptr _boss_bgm_title, di
 	repne scasb
 	lea	ax, [di+5]
-	mov	_tile_index_ptr, ax
-	mov	_tile_row, 0
+	mov	_tile_section_ptr, ax
+	mov	_tile_row_in_section, 0
 	movzx	ax, byte ptr es:[di]
 	inc	ax
 	add	di, ax

th05_main.asm

@@ -1783,7 +1783,7 @@ sub_BB9A	proc near
 		push	di
 		push	si
 		push	ds
-		mov	bx, _tile_index_ptr
+		mov	bx, _tile_section_ptr
 		sub	bx, 4
 		mov	di, offset _tile_ring
 		add	di, TILES_MEMORY_X * (TILES_Y - 1) * 2
@@ -1942,10 +1942,10 @@ loc_BD36:
 		mov	bx, _std_seg
 		mov	es, bx
 		assume es:nothing
-		dec	_tile_row
+		dec	_tile_row_in_section
 		jns	short loc_BD88
-		mov	_tile_row, 4
-		inc	_tile_index_ptr
+		mov	_tile_row_in_section, 4
+		inc	_tile_section_ptr
 		inc	_tile_scrollspeed_ptr
 		mov	bx, _tile_scrollspeed_ptr
 		mov	dl, es:[bx]
@@ -1965,9 +1965,9 @@ loc_BD88:
 		add	ax, offset _tile_ring
 		mov	di, ax
 		xor	ax, ax
-		mov	al, _tile_row
+		mov	al, _tile_row_in_section
 		shl	ax, 6
-		mov	bx, _tile_index_ptr
+		mov	bx, _tile_section_ptr
 		mov	bl, es:[bx]
 		xor	bh, bh
 		mov	bx, [bx+870h]