XML:XML Modding Lessons

This article builds on the general introduction to modding found at Modding Oni.

The XML namespace is devoted to explaining Oni's data types in plainer English than the technical documentation at OBD, and provides tutorials in XML modding.

Oni's resources could be separated into one of two categories: media (such as textures and sounds), and non-media (such as character class data). Most of the non-media data can be exported to XML. This allows much easier modding than the hex-editing of the old days (compare the two methods here). Some media resources can also be edited as "XML", referring to the fact that an XML file will be created alongside the resource's image/sound file when it is exported from the game data, and this XML companion file contains metadata about the media resource that allows OniSplit to re-import the resource when you are done editing it.

To learn what the different resource types do, and to see which types can be edited through XML, see the database link below. Though XML modding can generally be done with nothing more than OniSplit's command line interface and a text editor, the tutorials linked below are written with the Anniversary Edition in mind, because the AE provides modding tools (including a GUI for OniSplit), gives you a framework for testing your mod package, and globalizes more of Oni's data so it can be used in any level.

Working with XML files

Code folding in Visual Studio 2019.

Xcode 12. If you don't see the code folding ribbon, see Preferences… > Text Editing > Display > Code folding ribbon.

EXtensible Markup Language is a plain-text file format designed to be both human-readable and machine-readable. It stores data in-between tags, e.g. <Data>Some data here</Data>, and these tags can be arranged in a hierarchy to keep things organized. The only technical difference between a normal text file and an XML file is that the file name ends in ".xml" instead of ".txt" and that it typically begins with the string <?xml version="1.0" encoding="UTF-8" ?>. You can thus edit an XML file in any text editor, such as Notepad in Windows and TextEdit on the Mac.

See the tutorials below to learn how to extract game data as XML, modify it, and get it back into Oni.
Capitalization matters: OniSplit is case-sensitive when it processes the XML.
Text indentation: Most tags have some indentation (tabs). It is not required by OniSplit but it helps one get an understanding of the hierarchy. Two examples:

Good:

   <Instance id="4" type="IGSA">
       <Strings>
           <Link>#7</Link>
       </Strings>
   </Instance>

Bad:

   <Instance id="4" type="IGSA"><Strings><Link>#7</Link></Strings></Instance>

Code folding: A simple text editor (and good use of the search function) is actually enough to work with Oni's XML. But big files might be easier to handle with what programmers call "code folding". Code folding allows you to collapse tags in order to get a better sense of the overall file structure, and is found in IDEs like Microsoft Visual Studio (Windows) and Xcode (Mac). Both programs are free.

File comparison: For comparing two versions of an XML file to find the changes, you can use WinMerge (Windows) or FileMerge (Mac, comes with Xcode). Note that if one file has passed through Oni, the data may have been totally reordered and cannot be diff-gazed effectively.