Edit the Town Map

The Town Map is a bit tricky to edit: it's one of the only things in pokecrystal that still requires a hex editor. (Some free hex editors for Windows are FlexHEX, HxD, Frhed, wxMEdit, Catch22 HexEdit, or wxHexEditor.) This tutorial will explain how it works.

Contents

1. The tileset
2. The color palettes
3. The Johto and Kanto tilemaps
4. The landmarks
5. GSC Town Map Editor
6. Remove the gray border for more map area

1. The tileset

Like everything else on the GameBoy, the Town Map is composed of 8x8-pixel tiles. Its tile graphics are stored in gfx/pokegear/town_map.png:

You can freely edit this image to change the tiles, but you can't make it larger. That's because all the available tileset space is taken up by Pokégear and font graphics. You can see this in BGB's VRAM viewer:

(If you want to add more tiles, there are those three unused blank ones on the right side of the tileset. You can also replace the two "-TO" tiles of "KANTO", since they're identical to the "JOHTO" ones.)

2. The color palettes

The tileset image is grayscale, but it's colorful in-game. The colors are defined in gfx/pokegear/pokegear.pal and gfx/pokegear/pokegear_f.pal. Each file defines six palettes: for the gray border, the green-on-blue earth, the brown-on-green mountains, etc.

You can view the palette with BGB's VRAM viewer again:

Anyway, gfx/pokegear/town_map_palette_map.asm defines the correspondence between tiles and colors. For example, notice how the nine MOUNTAIN entries in that file correspond with the nine mountain tiles in gfx/pokegear/town_map.png.

3. The Johto and Kanto tilemaps

The two regions' maps are actually defined by gfx/pokegear/johto.bin and gfx/pokegear/kanto.bin. Each of those is a 361-byte binary tilemap: 20x18 bytes covering the entire screen, from top-left to bottom-right, with a $FF at the very end. The bytes are tile IDs, starting at 0. For example, $0A (10 in decimal) is the eleventh tile in the tilemap, the town or city icon. And if you look at where the $0A bytes are in johto.bin and kanto.bin, you'll notice they correspond to the locations of towns and cities.

If your hex editor supports coloring by value, that can make editing a lot easier. For example, here's Hex Workshop (not a free program) using a custom color map to highlight different tile IDs:

Clearly, those bytes represent these Town Maps:

4. The landmarks

Landmarks are defined in data/maps/landmarks.asm. Each one has an X coordinate, Y coordinate, and name. The coordinates are in pixels from the top-left corner of the 160x140-pixel screen. For example:

	landmark 140, 100, NewBarkTownName

...

NewBarkTownName:     db "NEW BARK¯TOWN@"

If you look at pixel coordinates (140, 100) in the Johto map above, you'll see it's in the middle of the New Bark Town icon:

Be careful, though! Currently pokecrystal defines the landmark macro like this:

landmark: MACRO
; x, y, name
	db \1 + 8, \2 + 16
	dw \3
ENDM

But versions older than July 18, 2018 define it like this:

landmark: MACRO
; x, y, name
	db \1, \2
	dw \3
ENDM

This means that older versions of pokecrystal have their landmark X coordinates increased by 8 and their Y coordinates by 16. For example, New Bark Town used to be at (148, 116).

If you're wondering why those offsets exist, it's because of how the GameBoy hardware works. From the Pan Docs:

Byte0 - Y Position Specifies the sprites vertical position on the screen (minus 16). An offscreen value (for example, Y=0 or Y>=160) hides the sprite.

Byte1 - X Position Specifies the sprites horizontal position on the screen (minus 8). An offscreen value (X=0 or X>=168) hides the sprite, but the sprite still affects the priority ordering - a better way to hide a sprite is to set its Y-coordinate offscreen.

For more information on editing landmarks, see the tutorial on how to add a new map and landmark.

5. GSC Town Map Editor

Step 3 described how to edit the tilemaps using a hex editor, but it can be a visual pain to do so. An alternative is the GSC Town Map Editor program by Harrison.

Usually you shouldn't use old binary hacking programs with the disassembly, but this program has an Export Map function, which creates a .map file that's (almost) exactly the same as pokecrystal's .bin files.

First, download and unzip the program. Two files it includes are GSC Town Map Editor.exe and tileset.bmp. The tileset.bmp image is used by the program to render the Town Map; it's twice the size of town_map.png and uses colors. You can use MS Paint to resize and color town_map.png and save it as tileset.bmp. The download already includes an appropriate tileset.bmp for default GSC:

Then run GSC Town Map Editor.exe, open your ROM with File→Open, and pick a region to edit. You'll see something like this:

When you're done making edits, go to File→Export Map and overwrite johto.bin or kanto.bin. (The default extension is .map, but you can enter .bin instead.) The only difference between the exported file and the original is that GSC Town Map Editor does not put $FF at the end. So edit engine/pokegear/pokegear.asm:

 JohtoMap:
 INCBIN "gfx/pokegear/johto.bin"
+	db $ff

 KantoMap:
 INCBIN "gfx/pokegear/kanto.bin"
+	db $ff

Now your edited map will show up when you rebuild the project!

Note that GSC Town Map Editor, like most old binary hacking tools, makes assumptions about the exact addresses of various content in the ROM. If you make extensive edits to the disassembly project, the addresses could change. Then you'll get an "Access violation" error when you try to pick a region. If that happens, you'll just have to use a hex editor.

6. Remove the gray border for more map area

If you're making a large region, you may want to get rid of the gray border around the map to make room for more terrain. But there's more to it than just redesigning the .bin files without any border tiles. The top three rows of tiles are covered by the Pokégear interface, the map name, and the "Where?" prompt when using Fly.

You can minimize those elements by making them only take up two rows. Edit engine/pokegear/pokegear.asm:

 InitPokegearTilemap:
 	...

 .Map:
 	ld a, [wPokegearMapPlayerIconLandmark]
 	cp FAST_SHIP
 	jr z, .johto
 	cp KANTO_LANDMARK
 	jr nc, .kanto
 .johto
 	ld e, 0
 	jr .ok

 .kanto
 	ld e, 1
 .ok
 	farcall PokegearMap
-	ld a, $07
-	ld bc, $12
-	hlcoord 1, 2
-	call ByteFill
-	hlcoord 0, 2
-	ld [hl], $06
-	hlcoord 19, 2
-	ld [hl], $17
 	ld a, [wPokegearMapCursorLandmark]
 	call PokegearMap_UpdateLandmarkName
 	ret

 _TownMap:
 	...

 .InitTilemap:
 	ld a, [wTownMapPlayerIconLandmark]
 	cp KANTO_LANDMARK
 	jr nc, .kanto2
 	ld e, JOHTO_REGION
 	jr .okay_tilemap

 .kanto2
 	ld e, KANTO_REGION
 .okay_tilemap
 	farcall PokegearMap
-	ld a, $07
-	ld bc, 6
-	hlcoord 1, 0
-	call ByteFill
-	hlcoord 0, 0
-	ld [hl], $06
-	hlcoord 7, 0
-	ld [hl], $17
-	hlcoord 7, 1
-	ld [hl], $16
-	hlcoord 7, 2
-	ld [hl], $26
-	ld a, $07
-	ld bc, NAME_LENGTH
-	hlcoord 8, 2
-	call ByteFill
-	hlcoord 19, 2
-	ld [hl], $17
 	ld a, [wTownMapCursorLandmark]
 	call PokegearMap_UpdateLandmarkName
 	farcall TownMapPals
 	ret

 TownMapBubble:
 ; Draw the bubble containing the location text in the town map HUD

 ; Top-left corner
-	hlcoord 1, 0
+	hlcoord 0, 0
 	ld a, $30
 	ld [hli], a
 ; Top row
-	ld bc, 16
+	ld bc, 18
 	ld a, " "
 	call ByteFill
 ; Top-right corner
 	ld a, $31
+	ld [hli], a
-	ld [hl], a
-	hlcoord 1, 1
-
-; Middle row
-	ld bc, 18
-	ld a, " "
-	call ByteFill
-
 ; Bottom-left corner
-	hlcoord 1, 2
 	ld a, $32
 	ld [hli], a
 ; Bottom row
-	ld bc, 16
+	ld bc, 18
 	ld a, " "
 	call ByteFill
 ; Bottom-right corner
 	ld a, $33
 	ld [hl], a

 ; Print "Where?"
-	hlcoord 2, 0
+	hlcoord 1, 0
 	ld de, .Where
 	call PlaceString
 ; Print the name of the default flypoint
 	call .Name
 ; Up/down arrows
 	hlcoord 18, 1
 	ld [hl], $34
 	ret

Now you'll have more regional real estate: