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How To: Change an Existing Mod

A common first step into modding is to have a look at existing work.

What you need:

ModOp Basics

First you need to have a basic understanding how XML patches work.

All XML files in mods have several entries like the following:

<ModOp GUID='100780' Type='addNextSibling'>
  <!-- stuff in here -->
</ModOp>

Those are ModOps. They add, remove or change assets in the game. You need to know more about them, if you want to change more than some simple values.

Change Maintenance

Let's start with a simple example. You want to change the maintenance cost of Nate's Windmill.

Finding the GUID

GUIDs are unique identifiers. Every game object definition aka Asset has one.

First you need the building. You can do that by searching "Nate's Windmill" in data\config\gui\texts_english.xml. Hint: you can hit Ctrl+Shift+F in Visual Studio Code to quickly search all files.

You'll find an entry with text and it's GUID.

<Text>
  <GUID>1500010001</GUID>
  <Text>Nate's Windmill</Text>
</Text>

Finding the Asset

It's easy to find the asset when you search for the GUID. The result should look like this:

<ModOp GUID='100780' Type='addNextSibling'>
  <Asset>
    <Template>JakobPowerplantWithRadius</Template>
    <Values>
      <Standard>
        <GUID>1500010001</GUID>
        <Name>nates_windmill</Name>
        <IconFilename>data\jakob\nates-windmill\icon_nates_windmill.png</IconFilename>
        <InfoDescription>1500010004</InfoDescription>
      </Standard>
      <!-- ... -->

Usually you find stuff you want to change in data\config\export\main\asset\assets.xml but in this case it's actually data\jakob\nates-windmill\assets.include.xml. Especially more recent mods have their assets distributed across several files.

Understanding the Asset

General structure of an asset.

<Asset>
  <Template>template name</Template> <!-- or sometimes <BaseAssetGUID> -->
  <Values>
    <Standard>
      <GUID>1500010001</GUID>
      <Name>random name</Name> <!-- not used in-game -->
      <!-- -->
    </Standard>
    <A>
      <!-- -->
    </A>
    <B>
      <!-- -->
    </B>
    <C>
      <!-- -->
    </C>
  </Values>
</Asset>

Assets have a Template or an BaseAssetGUID. They define what features aka property sections that asset has within Values.

They always have a Standard property section, definining the GUID and other things.

The remaining property sections vary a lot.

⚠ Note: the game crashes when there is a property section that is not defined in the template. This was a common reason for crashes with GU16.

Changing the Maintenance

If you scroll a bit through the asset of Nate's Windmill, you'll find a Maintenance property section.

<Maintenance>
  <IncomeCategory>ProductionBuildings</IncomeCategory>
  <Maintenances>
    <Item>
      <Product>1010017</Product> <!-- Coins -->
      <Amount>400</Amount>
    </Item>
    <Item>
      <Product>1010115</Product> <!-- Workers -->
      <Amount>20</Amount>
      <ShutdownThreshold>0.5</ShutdownThreshold>
    </Item>
  </Maintenances>
</Maintenance>

You can change here the amount of coins or workers needed. Or even exchange and add/remove furter maintenance Items.

The number in Product is just another GUID.

You can use Schwubbe's online Asset Search to figure out the GUID of engineers for example.

Pitfalls and Best Practices

Delete .cache

Always delete the .cache folder in mods/. The modloader doesn't recognize changes in *.include.xml files for example.

Change gets overwritten

Sometimes mods add an asset and have in other XMLs instructions to change individual values.

⚠ These cases are too complicated for beginners, but usually you don't need to touch them.

An example in Nate's Windmill is the IndustrializationDistance. It is defined in the asset once, but there is another instruction in cheats.include.xml that overwrites it. Especially mods that provide iModYourAnno tweaks will have that.

In nates-windmill/assets.include.xml:

<Powerplant>
  <IndustrializationDistance>6</IndustrializationDistance>
</Powerplant>

In cheats.include.xml:

<ModOp GUID="1500010001" Type="replace"
       Path="/Values/Powerplant/IndustrializationDistance"
       ModOpID="Range" Skip="1">
  <IndustrializationDistance>6</IndustrializationDistance>
</ModOp>
<!-- ... -->
<ImyaExpose Path="self::*" ModOpID="Range" Kind="Slider" ExposeID="Range"
            Description="Increase electricity range.">
  <SliderDefinition Min="6" Max="16" Stepping="2" />
</ImyaExpose>