Technical Details

Most of you are here to create games without having to look under the hood, but for the curious ones, here's a brief overview of how everything works.

Architecture

GBA Studio is mostly an Electron app with a CLI companion. You can either use the app itself to create games, or write JSON files manually to define your game's structure and content and build the game using the CLI.

Engine

During build, GBA Studio transforms JSON content files into C++ code using Handlebars templates.

For example, here's the code used to define the fade-in event:

{{else if (eq this.type "fade-in")}}
{{>valuePartial prefix=(concat ../prefix "_" @index "_duration") value=this.duration}}
constexpr bn::string_view {{../prefix}}_{{@index}}_type = "fade-in";
BN_DATA_EWRAM neo::types::fade_event {{../prefix}}_{{@index}}({{../prefix}}_{{@index}}_type, &{{../prefix}}_{{@index}}_duration_value);

The C++ code uses Butano, an extraordinary project made by Gustavo Valiente that provides a high-level framework for developing Game Boy Advance games.

Almost everything is put into the ROM (using constexpr), with some exceptions for events that manipulate runtime data that are put into EWRAM (using the BN_DATA_EWRAM macro).

Disclaimer: Last time I did C++ was during my license degree, so doing all of this was a real challenge. Expect things to be a bit messy and not perfectly optimized in a C++ fashion (pointers are my nemesis).

Dynamic Values

Because I wanted GBA Studio to be almost equal to GB Studio (emphasis on almost), I also had to implement "Dynamic Values" that allow to use runtime data (variable, player position, etc.) without any code knowledge by the end user.

In order to do this, and because we don't know the type of these dynamic values at compile time, we need to store every types into one common structure.

For example, if I set my fade-in event duration to 200, in the generated C++ code, it will be stored as:

• int -> 200
• bn::string_view -> "200"
• bool -> true
• bn::fixed -> 200.0

This drawback is a necessary evil to allow dynamic values to be used seamlessly within the engine, especially into if conditions: