Here is where our romhack currently stands:

1. Changing Professor Birch’s speech
2. Changing the Littleroot Town map
3. Adding an interaction event in Littleroot Town
4. Changing the starter Pokémons
5. Changing the first trainer’s team
6. Modifying the first wild Pokémons

Goal

The goal for this step is to modify the starting town’s map, and add an object we will later be able to interact with. This object will most likely be a signpost, or npc, or one of both.

To make these changes, we are going to use Porymap, available here.

Using Porymap

Once you’ve compiled and executed the Porymap binary and opened the relevant project, our romhack in this case, you should an interface that is reminiscent of the typical RPG Maker interface.

The leftmost panel should be a list of folders named gMapGroup0 through gMapGroup33 at the time of writing. Here is what each map group contains:

• gMapGroup0: all of the “outside” maps - town layouts and routes
• gMapGroup1 to gMapGroup16: all of the “indoor” maps for the towns, with some exceptions like the inside of the moving truck found during the introduction in Littleroot Town
• gMapGroup17 to gMapGroup23 and gMapGroup27 to gMapGroup33: all of the “indoor” maps for all of the routes
• gMapGroup24 to gMapGroup26: all of the remaining “indoor” maps - Battle Frontier, caves, the inside of the moving truck, ships, etc…

Take a moment to unroll of the folders and take a look at all of the different maps you can edit. Once you’re done, open gMapGroup0 and select [0.09] LittlerootTown.

You should now see the town map in the center of your screen, and the map’s tiles on the right. The rest of the interface is intuitive enough and I will let you refer to the official documentation to see exactly what everything does.

Making our first map change

Littleroot Town currently looks like this:

Let’s add a puddle, and a signpost in the center and save our changes:

Congratulations, you’ve just edited your first map! However, as you might realise, if you compile the rom and play it, the player goes right through the signpost.

We now have to add collisions. To do so, select the Collision tab on the right, and make it so the player cannot walk through the signpost. The map’s collision look like this:

Save the map, compile the game, and you will see that the player cannot walk through the signpost anymore:

Congratulations once again, you’ve successfully edited a map and adjusted the collisions!

Interacting with the signpost

Switch to the events tab in the central panel, select the dropdown menu on the right, next to New Object and choose New Sign. A new sign event should appear in the top left corner (0,0) of the map. Select the pointer and move the event to the signpost in the middle of the puddle.

Name the script LittlerootTown_EventScript_PuddleSign and click the Open Map Scripts button. If nothing happens, open the data/maps/LittlerootTown/scripts.inc file with the text editor of your choice.

Add this code at the end of the file:

LittlerootTown_EventScript_PuddleSign::
	msgbox LittlerootTown_Text_PuddleSign, MSGBOX_SIGN
	end

LittlerootTown_Text_PuddleSign:
	.string "Welcome to the world famous Littleroot\n"
	.string "Town puddle$"

As you can imagine, this code creates a procedure called LittlerootTown_EventScript_PuddleSign which creates a message box containing the text after the LittlerootTown_Text_PuddleSign label. Save the file, recompile the game, and you should now be able to interact with the signpost:

Good job, you’ve now added your first interactive event to game and made a more complete romhack!

That’s it for now, next time we will edit the game’s starter pokémons.

The goal of this project is to create a Pokémon Emerald romhack. To do so, we are going to use a dissassembled version of the rom as a starting point. Using different tools, we are going to modify the parts we want to change. The changes we are going to make are the following:

1. Changing Professor Birch’s speech
2. Changing the Littleroot Town map
3. Adding an interaction event in Littleroot Town
4. Changing the starter Pokémons
5. Changing the first trainer’s team
6. Modifying the first wild Pokémons

Tools

Here is a list of the tools we are going to use:

A Pokémon Emerald disassembly

• pokeemerald - Github

A map editor

• Porymap - GitHub

A Gameboy Advance emulator (any will do)

• Visual Boy Advance M - GitHub

A text editor (any will do)

• Visual Studio Code - GitHub

Setting up each of these tools is well documented and can be done without too much of a hassle. Personally, I am working on a 2019 Dell XPS 13 running Arch Linux, and all of these tools are usable without issues.

Making our first change

Right now, when we start the game we get the usual speech from Prof. Birch:

Let’s change his opening line

Hi! Sorry to keep you waiting!

to

Hey all you cool cats and kittens!

To do so, start up your text editor and open the data/text/birch_speech.inc file in the pokeemerald repository. You should see this as the first 7 lines of the file:

gText_Birch_Welcome:: @ 82C897B
 	.string "Hi! Sorry to keep you waiting!\p"
	.string "Welcome to the world of POKéMON!\p"
	.string "My name is BIRCH.\p"
	.string "But everyone calls me the POKéMON\n"
	.string "PROFESSOR.\p"
	.string "$"

From this sample, we can determine that the \p character indicates when user input, typically the A button, is needed to go to the next line of dialogue, and that the \n simply indicates a line break in the dialogue.

In our case all we have to do here is to change the second line to

    .string "Hey all you cool cats and kittens!\p"

Now save the file, compile the rom, start a new game in your emulator and you should see:

Congratulations, you’ve just made your first romhack ! Take a look at the other lines of dialogue in the file, try to find other files that contain NPC dialogue, modify them and see what happens.

Next time, we will explore how to customize the Littleroot Town map !