Hearts of Iron IV - Development Diary 52 - Modding

Hi everyone, this weeks diary is going to get really technical! We will be talking modding and improvements we have made for the modders in HOI4. This is also going to be a very long one :) When starting out we decided we wanted to make HOI4 our most moddable game yet. That meant not hard coding things (HOI3 had a lot of hard coded logic and references to certain nations). In HOI4 all these things are in soft code, or part of scenario script setups making it a much better platform for cool mods. We have also decided to include the tool we use (more further down), and while it is provided as-is and not really polished compared to the real game its very useful. The game is also much better at letting you know when you have made mistakes and everything that can go wrong will usually let you know with logs etc. Tools and Getting Started Getting started with the creation of mods are now easier than ever before! Using the launchers mod tool will allow you to create an empty mod for the game without any hassle and without even starting the game.

Then starting the game with the “--debug” flag will enable the “modder mode” that adds some extra sanity checks and enabling tools useful for modifying the game. For example the in game Nudger tool that provides a simple interface to modify the properties of the map.

Here I created the awesome state of Östergötland by redistributing some provinces from Småland and tweaked the positions of the buildings. The Nudger tool will then validate my changes and save them to the appropriate files for me and my mod, just in a few mouse clicks. These files are of course human readable and can easily be edited with your favorite text editor for more advanced scripting or making smaller changes, most of the files (like state history setup) also have the option to be opened with a external program from the Nudger so you do not even need to find them in the filesystem.

Another nice tool is the instant feedback system aka “Error Dawg” appearing in the lower right corner that will give you instant feedback about scripting errors and oddities during gameplay. Clicking on it will of course open the error log for you, painfully reminding you about things you have forgotten or otherwise faulty scripted.

When satisfied with your mod and fixed all the errors you are just one click away from sharing it with the rest of the HoI4 community by uploading it to the steam workshop with the Mod tool.

Another thing we have put a lot of effort into is reloadability. You can reload interfaces (even automatically as the game will check if files are modified and you will see changes instantly ingame) as well as several game systems. For example focus trees will reload with your changes making it really quick and easy to work with making them and not forcing you to restart the game all the time. Scripting & Language Improvements One of the small help functions we’ve put in is the console command “trigger_docs”. This will print a list of all the triggers and effects we have in the game along with a small description of how they are used. We hope this can be a useful tool for new modders to find what they’re looking for and old modders to discover hidden possibilities.