An Introduction to GD Modding (using Geode)

Hello everyone! This is an introduction to GD Modding (using Geode), a handbook that covers all of the essentials of GD Modding. To follow along with this handbook, you will need to have Geode installed. This handbook is written as a tutorial for beginners, though even if you are an experienced GD modder already, getting a fresh-up on the basics can never do harm. Even if for some reason you don’t use Geode, this handbook still contains general information about modding and GD modding specifically, however all practical code examples and the code project we will build later will use Geode.

Prerequisites

Do note that while this handbook is written for people with little to no previous experience modding GD, previous programming and computing knowledge is assumed. It is highly recommended that before you start GD modding, you should at the very least know how to use C++. (Knowledge of other programming languages is also good, but the closer to C++ the better)

If you’re unsure that you have sufficient programming skills, here’s a list of concepts you should at the very least know:

• Control flow
• Variables
• Functions
• Data types
• Classes
  • Inheritance (including multiple inheritance)
• Namespaces
• The C++ Standard Library
• Pointers & references (if you don’t know how pointers work, you can get through this tutorial, but you will also be in big trouble later on)
• Macros and the C++ Preprocessor
• Difference between compile-time and runtime

Other concepts that are very good to know beforehand but not strictly required:

• X86 Assembly (doesn’t mean you should speak or read it fluently; just know what it is)
• Reverse enginering (the basics of using Ghidra will be explained in Volume 2)

If some of the items in the list aren’t familiar to you, you should read up on some online resources first. A good place to start is to just write “C++ tutorial” in Google and see what comes up. If only some specific parts are unfamiliar, for example you don’t know how namespaces work, search for “C++ namespaces”.

Volumes

This handbook is collected into ?? Volumes, going over the following material:

• Volume 1: The basics of modding (Hello, World!)

• Volume 2: Reverse engineering

• Volume 3: Geode, working with other mods, and publishing your mod

• Volume 4: Making a mod (Project)

How to read this handbook

It is recommended to read through the book chapter-by-chapter. Important concepts and keywords are highlighted in bold. Variables, functions, registers and all other code entities are written like this. Code blocks look like this:

#include <iostream>

int main() {
    std::cout << "Hi mom!\n";
}

The language presented in the code blocks should be stated right before or after the block in the text, but the majority of code blocks use C++.

⚠️ This is what a warning looks like. If you see one of these boxes, pay close attention; it contains tips about how to avoid common mistakes in modding.

ℹ️ This is what an info box looks like. It contains general information about the current topic that you might find useful.

📗 These boxes may also contain links to further reading materials for the interested.

Sometimes the text has notes like this [Note 1]. They are explained at the end of the paragraph, or at the end of the text at the Notes section.

[Note 1] This is what an explanation of a note looks like.

“Traditional” Mods

Many things in this handbook are referred to as “traditional modding”. This means mods made and modding methods used in 2.1; Geode is currently the only major mod loader available for 2.2 and beyond, and differs in some major ways from traditional modding practices. Traditional practices are still included in this tutorial however as a historical curiosity, and to help you spot where old tutorials differ from modern practices.

Ready, set, go!

And with that, let us start with Chapter 1.1!