Modding

Development Showcase: Modding

Hiya, it's Caleb, developer of Harwell. If you've been keeping up with these I'm sorry for the delay on this one! I've been focusing hard on improving Harwell and rewriting large sections of it to be more modular so I can build the game with modding in mind.

Changes

One thing I was thinking about was moddability and modularity in the game's design. I potentially want to open the game up for modding, even just the foundations of it for now, and needed to consider this in how I design and implement features. I realised that I'd better do this sooner rather than later, as it required rewriting large parts of the code in a way that would open the game up for modding.

In order to do this I had to implement a way for the game to have it's base game resources and then check for additional content and mods when loaded up that it can overwrite the base resources with.

I also had to implement a way for the game to generate the relevant UI based on the modded entries. Previously, the resources in the market menu and the build buttons were hardcoded. I had to redesign the entire UI and write the scripts to automatically deploy those same entries using the JSON data and texture files.

Decisions

One of the tricky decisions was how to open up the game. There's two ways I could implement modding: a custom solution using JSON files or similar, and modding via PKG files that can be loaded as additional content.

PKG Files

Using the in-built features of Godot I can allow players to create their own complete packages and have the game load them up. This would mean modders would have to use Godot to create the mods, be familiar with Godot, and then know how to properly structure the mods and export it to use in-game.

One danger of this solution is it allows modders to implement any feature they want - for a game that will be Multiplayer this is especially dangerous as people could load malicious features into game scripts or exploit the game. Modders would have full access to the game and can work out how to best exploit it.

I could sanitise the mods loaded to remove the chance of that happening but it doesn't solve the problem of having to use the Godot engine and I wanted something more seamless.

Custom Solution

Inspired by Paradox Interactive games, I considered a custom solution using JSON files that means I could define the game's resources, buildings, parameters, etc. in JSON files that the game deploys. Players can then change, remove, or add JSON files and change how the game works that way. It would be moderated, very easy to use (would just need notepad), and I can keep the core of the game uneditable to avoid people changing parts of the game that could be a problem. The downside is I have to implement every kind of resource I want to be moddable and have the game read those mod files.

I may regret it, but I chose to implement the custom solution.

Difficulties

I quite quickly found out it was going to be much more work than I expected, even after carefully considering how I can implement it. I've had to build a resource loader than checks the game files, deploys the game's base files to the user directory, and then reads those files to use in-game. This resource loaders currently knows how to interpret resource files and building files, but I plan to implement more features soon. For now, that'll do.

Another thing I had to do was go through and redesign all of my resources and buildings as JSON files. Originally, they were nodes in Godot with scripts attached and modified via the engine or script. I kept most of the script the same, except it loads the script up with the values held in the JSON file.

The buildings were the same, I've had to allow buildings to be defined in the JSON files, these are then read by the build menu manager script that generates the construction buttons, reads the graphics folder for the textures (also moddable), and then loads the relevant building node to place it in game. I still haven't implemented the actual buildings themselves as this will take a bunch more work so I've put that off for now while I work on more important features. The main thing was understanding how it was all going to work together. The actual buildings will need textures, particle effects, lighting, shaders, etc. The textures aren't the difficult bit as I could easily make those moddable, but controlling custom particle effects (e.g. chimney smoke for Steel Mills) and lighting is more tricky via JSON and I may need a more robust solution for this (would love any suggestions!). I may have to make the buildings more generic or create a building mod making menu in-game.

Implementation

Currently, both resources and buildings are (mostly) moddable. The game deploys the base resources to the user:// directory and then reads those files every time the game is launched. The player can modify those directories and the game will load up the changes on next boot. I'll need to develop this further to support Steam Workshop and easily enabling/disabling mods but it's a start!

The moddable folders.

The data\\resources folder.

These files contain the important information for the resource, and the market automatically reads it, loads it into the game, and creates a market entry for it.

Modding a resource is as simple as changing the JSON file and reloading the game!

Example of a resource file.

Example building file.

There's still some adjustments I need to work on, such as localisation support, so the specific entries in these files may change as time goes on.

Checksum

In order for the mods to support multiplayer, I also implemented checksums (also strongly inspired by Paradox). The game calculates a short 8 character string to act as the checksum, this is generated based on the contents of the files in the user directory. Any modified game files will change this, ensuring that players can only join and play in games with the same checksum. Now to properly test multiplayer and implement the lobby system!

Cheers, that's all from me for this showcase. I'll try and keep more on top of these, I've got a lot lined up to show including a bunch of QoL features I've implemented such as profit calculations, auto-selling, and more, and I'm fleshing out the multiplayer game sessions and lobby systems currently.

Have a great week,

Caleb