Modding Tutorials/Essence

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If you have a high-level understanding of what your mod will do, this page will give you a basic understanding of how to approach it. Further pages will explain how to actually go about this, but here we get you started. Don't get frustrated if not all of this makes sense to you yet.


Modding Difficulty

So how hard is it to mod RimWorld? Overall, RimWorld is a modder-friendly platform actively supported by the game's creators.

  • Easy - Edit XML to apply existing functionality in new ways to make new things. (i.e. a new gun)
  • Easy (if you're an artist) - Create new RimWorld art and sound assets and add them to XML to use them.
  • Moderate (if you can code) - Create a C# class to make a new simple behavior. These C# classes can be incorporated via XML.
  • Harder: GUI programming
  • Hard: Complex inter-object behaviors
  • Hard: Create new AI behaviors


So you want to...

... Add a new Thing to RimWorld.

RimWorld uses XML to define the Things in RimWorld, in ThingDef XML entries. So, if you are going to create a new Thing, look in the Core XML files of RimWorld and duplicate a ThingDef entry for a similar item. Then, make the modifications to that entry to achieve your item. Remember, defName needs to be different for all entries.

Add a new Thing to RimWorld
Your Mod will have a new ThingDef entry in XML.
Add a new Thing to RimWorld, like an existing one
Read the Core XML and use one of the abstract XML definitions as a Parent. You'll inherit it's properties.
Add a new building or plant
As above, but make sure the category tag is set so your building tag gets used.


...Create new functionality.

The XML files are used to apply and adapt existing functionality in the code base in new ways, but for modders, many times this is not enough. If you need new functionality, you create that with C# code and apply it to your new Things with XML entries.

Create new functionality
If your required functionality doesn't exist, create a C# class to do it.
Create a Thing with new functionality
Create a new C# object "MyNamespace.MyNewClass" that inherits from Thing and a ThingDef XML entry that uses it with <thingClass> pointing to MyNamespace.MyNewClass.
Create a Thing with new XML specifiable properties
Create a new C# class with these new XML properties, that inherits from ThingDef. In your XML ThingDef entry, have 'Class="MyNamespace.YourThingDef".'


...Alter RimWorld code.

Sometimes, you need to change what existing code does. This can be done in both XML and C# code.

Alter a Core Thing's XML Entry
As of A17, there exists something called DefPatches to alter the XML of RimWorld, often with no effect upon other Mods. So, you could change the power consumption of a lamp or make Devilstrand plantable in new locations.
Alter a C# method
Harmony is the current best approach for enhancing existing RimWorld code by inserting code pre/post to an existing method being called. See HugsLib and Harmony.