[Decompilation] [th02] Stage tiles: Initial screen of a stage

Part of P0236, funded by Yanga.

th02/main/tile/tile.cpp

@@ -11,6 +11,8 @@
 #include "th02/main/playfld.hpp"
 #include "th02/main/scroll.hpp"
 #include "th02/main/tile/tile.hpp"
+#include "th02/formats/map.hpp"
+#include "th02/formats/mpn.hpp"
 
 // Terminology:
 // • Line: [TILE_W]×1 stripe within a tile
@@ -31,6 +33,21 @@ extern bool tile_dirty[TILES_X][TILES_Y];
 extern bool tile_column_dirty[TILES_X];
 // -----
 
+// Map tiles
+// ---------
+
+#define section_for_map_row(row, ret) \
+	/* Sneaky! That's how we can pretend this is an actual function that */ \
+	/* returns a value. */ \
+	(row >> MAP_BITS_PER_SECTION); \
+	ret = map[ret]; \
+	static_assert((1 << MAP_BITS_PER_SECTION) == MAP_ROWS_PER_SECTION);
+
+inline tile_image_id_t map_tile_image_at(int section, int row, int x) {
+	return map_section_tiles[section].row[row & (MAP_ROWS_PER_SECTION - 1)][x];
+}
+// ---------
+
 void pascal near tile_egc_copy_lines_8(vram_offset_t vo_dst, int image)
 ;
 void pascal near tile_egc_copy_8(vram_offset_t vo_topleft, int image)
@@ -66,6 +83,42 @@ void pascal near tile_grcg_clear_8(vram_offset_t vo_topleft)
 	} \
 }
 
+void pascal near tile_row_put_8(screen_x_t left, vram_y_t top, int row)
+{
+	int section = section_for_map_row(row, section);
+	for(int tile_x = 0; tile_x < TILES_X; tile_x++) {
+		int image = map_tile_image_at(section, row, tile_x);
+		mpn_put_8((left + (tile_x * TILE_W)), top, image);
+	}
+}
+
+void tiles_fill_and_put_initial(void)
+{
+	int x;
+	int section;
+
+	// Skips the last row in the [tile_ring] (at (TILES_Y - 1)) because there's
+	// no data to fill it with and it's covered by black TRAM cells on the
+	// initial screen of a stage anyway.
+	// ZUN landmine: This function only blits to one VRAM page, with the other
+	// one being covered by tiles_render_all(). That function does actually
+	// render the entire tile ring, including the row we skipped here.
+	// Initializing that row at least with *something* might therefore be
+	// better than skipping it.
+	for(int y = 0; y < ((PLAYFIELD_H / TILE_H) + 1); y++) {
+		tile_row_put_8(
+			PLAYFIELD_LEFT, (PLAYFIELD_BOTTOM - TILE_H - (y * TILE_H)), y
+		);
+
+		section = section_for_map_row(y, section);
+		for(x = 0; x < TILES_X; x++) {
+			tile_ring[(PLAYFIELD_H / TILE_H) - y][x] = map_tile_image_at(
+				section, y, x
+			);
+		}
+	}
+}
+
 void pascal tiles_invalidate_rect(
 	screen_x_t left, vram_y_t top, pixel_t w, pixel_t h
 )

th02/main/tile/tile.hpp

@@ -67,6 +67,12 @@ static const vram_x_t TILE_AREA_VRAM_LEFT = (TILE_AREA_LEFT / BYTE_DOTS);
 	// redraw all tiles and then reset this flag to `false`.
 	extern bool tiles_egc_render_all;
 
+	// Fills [tile_ring] with the initial screen of tiles at the bottom/start
+	// of the map, and blits them to the playfield area in VRAM. Reads tile
+	// images from our data segment, the tile source area is neither read from
+	// nor written to.
+	void tiles_fill_and_put_initial(void);
+
 	// Marks all tiles for redrawing that lie within the given area of the
 	// screen.
 	void pascal tiles_invalidate_rect(

th02_main.asm

@@ -1262,121 +1262,7 @@ loc_453A:
 		retf	2
 sub_445A	endp
 
-
-; =============== S U B	R O U T	I N E =======================================
-
-; Attributes: bp-based frame
-
-sub_4540	proc near
-		push	bp
-		mov	bp, sp
-		sub	sp, 2
-		push	si
-		push	di
-		mov	ax, [bp+4]
-		sar	ax, 3
-		mov	di, ax
-		mov	al, _map[di]
-		mov	ah, 0
-		mov	di, ax
-		xor	si, si
-		jmp	short loc_458B
-; ---------------------------------------------------------------------------
-
-loc_455C:
-		mov	bx, di
-		imul	bx, (MAP_ROWS_PER_SECTION * TILES_X)
-		mov	ax, [bp+4]
-		and	ax, (MAP_ROWS_PER_SECTION - 1)
-		imul	ax, TILES_X
-		add	bx, ax
-		mov	al, _map_section_tiles[bx+si]
-		mov	ah, 0
-		mov	[bp-2],	ax
-		mov	ax, si
-		shl	ax, 4
-		add	ax, [bp+8]
-		push	ax	; left
-		push	word ptr [bp+6]	; top
-		push	word ptr [bp-2]	; image
-		nopcall	@mpn_put_8$qiii
-		inc	si
-
-loc_458B:
-		cmp	si, TILES_X
-		jl	short loc_455C
-		pop	di
-		pop	si
-		leave
-		retn	6
-sub_4540	endp
-
-
-; =============== S U B	R O U T	I N E =======================================
-
-; Attributes: bp-based frame
-
-sub_4596	proc far
-
-var_2		= word ptr -2
-
-		push	bp
-		mov	bp, sp
-		sub	sp, 2
-		push	si
-		push	di
-		xor	di, di
-		jmp	short loc_45F3
-; ---------------------------------------------------------------------------
-
-loc_45A2:
-		push	20h ; ' '
-		mov	ax, di
-		shl	ax, 4
-		mov	dx, 170h
-		sub	dx, ax
-		push	dx
-		push	di
-		call	sub_4540
-		mov	ax, di
-		sar	ax, 3
-		mov	[bp+var_2], ax
-		mov	bx, [bp+var_2]
-		mov	al, _map[bx]
-		mov	ah, 0
-		mov	[bp+var_2], ax
-		xor	si, si
-		jmp	short loc_45ED
-; ---------------------------------------------------------------------------
-
-loc_45CB:
-		mov	bx, [bp+var_2]
-		imul	bx, (MAP_ROWS_PER_SECTION * TILES_X)
-		mov	ax, di
-		and	ax, (MAP_ROWS_PER_SECTION - 1)
-		imul	ax, TILES_X
-		add	bx, ax
-		mov	al, _map_section_tiles[bx+si]
-		mov	bx, 23
-		sub	bx, di
-		imul	bx, TILES_X
-		mov	_tile_ring[bx+si], al
-		inc	si
-
-loc_45ED:
-		cmp	si, TILES_X
-		jl	short loc_45CB
-		inc	di
-
-loc_45F3:
-		cmp	di, 24
-		jl	short loc_45A2
-		pop	di
-		pop	si
-		leave
-		retf
-sub_4596	endp
-
+	extern @tiles_fill_and_put_initial$qv:proc
 	extern @TILES_INVALIDATE_RECT$QIIII:proc
 	extern @tiles_egc_render$qv:proc
 	extern @tiles_render_all$qv:proc
@@ -1966,7 +1852,7 @@ loc_B8B5:
 		add	sp, 0Ah
 		call	far ptr	palette_show
 		graph_accesspage 1
-		call	sub_4596
+		call	@tiles_fill_and_put_initial$qv
 		graph_accesspage 0
 		call	@tiles_render_all$qv
 		call	_mpn_free