File Loading

Introduction

A typical Gum project references many file types. Aside from the files created by the Gum tool (such as a .gumj file), a Gum project also references .png files and .fnt files.

Files referenced by your Gum project (as created in the Gum UI tool) automatically load their necessary dependencies assuming the files are part of the built file system. Usually your project game project should copy all Gum XML, PNG, and FNT files to the output folder. Gum does not use the MonoGame content pipeline.

Files in Gum Projects

When a file is added to a Gum project, the Gum UI tool checks the location of the file. If the file is not relative to the Gum project file (.gumj), the Gum UI tool warns you about the file being located outside of the project's folder. The tool recommends that the file should be copied so that your project remains portable.

If all of your project files are located relative to the .gumj root project file, then your project should be portable, and all referenced files will be automatically resolved for you when instantiating Screens and Components from your Gum project.

The Gum runtime library performs all of its loading from-file, so all of your files must be present in the destination directory. As explained in the Loading a Gum Project (.gumj/.gumx) page, all of your files should be set to Copy if newer in Visual Studio.

bear.png file set to Copy if newer

Loading Files Through Runtime Objects

Gum runtime objects can reference files. For example both SpriteRuntime and NineSliceRuntime can reference a Texture2D. Similarly, the TextRuntime type can reference BitmapFonts which are loaded from .fnt and .png files.

All runtime types support the assignment of these files by direct assignment of their appropriate type, or by string name.

For example, a Sprite's texture could be assigned either through the SourceFileName property or the Texture property:

// Initialize
SpriteRuntimeInstance.SourceFile = "bear.png";
// or
SpriteRuntimeInstance.Texture = MyTexture;

In the case of the SourceFile assignment, the SpriteRuntime loads the Texture2D from disk. By default the file is loaded relative to the Content folder.

Setting FileManager.RelativeDirectory

Whenever a file is assigned on a runtime object, Gum looks for the file in the ToolsUtilities.FileManager.RelativeDirectory directory. This directory defaults to your game's Content folder.

If you call GumService.Default.Initialize and pass a .gumj file, then RelativeDirectory is set to the directory containing the Gum project.

If your Gum project (.gumj) is located in the Content folder, RelativeDirectory is set to "Content/".

GumProject.gumj located in the Content folder

If your project is located in a subfolder of Content, then RelativeDirectory is set to the folder containing the Gum project. In this case, RelativeDirectory would be set to "Content/gum/"

Gum project in a subfolder

RelativeDirectory is used whenever files are loaded. These operations include:

• Calling ToGraphicalUiElement
• Assigning SourceFileName
• Setting custom or cached fonts on a Text object
• Setting states (which may assign variables)

It's recommended practice to set the RelativeDirectory to your Gum project's location and to leave it there so you never have to consider subfolders in any code that accesses files directly or indirectly.

Loading from a .gumpkg Bundle

In addition to loose files, Gum can load a project from a single-file .gumpkg bundle produced by gumcli pack. The path you hand to GumService.Initialize decides which one you get:

• A path ending in .gumj (or .gumx) loads loose files. This is the dev-time path, and hot reload works in this mode.
• A path ending in .gumpkg reads element XML, textures, and fonts from inside the bundle via FileManager.CustomGetStreamFromFile. No loose copy is needed in the output directory. MonoGame, KNI, FNA, and raylib load bundles; SkiaGum and Silk.NET read loose files only.

"Fonts" here covers both kinds: the baked FontCache .fnt and .png pages, and a .ttf the project rasterizes at runtime.

This means a published build can ship a single .gumpkg next to the executable instead of a folder tree of .gusx/.gucx/.png/.fnt files. See the pack page for the producer side and the runtime contract.

Serving Files From Your Own Source

FileManager.CustomGetStreamFromFile holds a function that takes a file path and returns a Stream. When you assign one, Gum reads through it instead of reading the filesystem. This is the same property the .gumpkg loader uses, and your game can assign its own. It covers every file Gum loads, .ttf files included, so a game that keeps its assets in a zip, an embedded resource store, or a download cache can run with no loose files on disk.

CustomGetStreamFromFile sits below the IContentLoader described further down. IContentLoader returns a finished object, such as a Texture2D. CustomGetStreamFromFile returns raw bytes and leaves Gum to parse them as it normally would.

Shipping September 2026: .ttf files reading through this function ships in the September release, or now if building Gum from source. Before this, Gum read a .ttf straight off the filesystem while every other kind of file went through the function.

File Caching

By default Gum caches loaded textures. In other words, the following code only results in a single file IO operation:

// Initialize
Sprite1.SourceFile = "MyFile.png";
Sprite2.SourceFile = "MyFile.png";

File caching can be disabled by setting the LoaderManager's CacheTextures property to false as shown in the following code:

// Initialize
LoaderManager.Self.CacheTextures = false;

Of course, doing so means that Gum will go to disk for every file which can increase load times and result in significantly more video memory usage.

Note that setting CacheTextures to false flushes the cache and disposes all cached content, so you can force the reload of all files by calling setting CacheTextures to false, then back to true as shown in the following code:

// Initialize
Sprite1.SourceFile = "MyFile.png"; // This loads the file from disk
Sprite2.SourceFile = "MyFile.png"; // This uses the cached Texture2D

LoaderManager.Self.CacheTextures = false; // This clears the cache:
LoaderManager.Self.CacheTextures = true;
Sprite1.SourceFile = "MyFile.png"; // This once-again goes to disk to load the file
Sprite2.SourceFile = "MyFile.png"; // This uses the cached Texture2D

LoaderManager.Self.CacheTextures = false; // This clears the cache
Sprite1.SourceFile = "MyFile.png"; // This once-again goes to disk to load the file
Sprite2.SourceFile = "MyFile.png"; // This also goes to disk to load the file

Be careful setting CacheTextures to false since all existing textures will be disposed. This means that if you have loaded textures which are still being referenced by runtime objects, you will get an exception if those are still being drawn after setting CacheTextures to false.

Customizing How Content Loads

By default Gum resolves a SourceFile name to a texture by reading a file from disk (relative to FileManager.RelativeDirectory). You can replace this behavior with your own logic. For example, you can load assets from a custom store, or hand back a texture your game engine has already loaded so the same image does not occupy video memory twice.

Gum performs all of its loading through an IContentLoader, which has two methods:

// Class scope
public interface IContentLoader
{
    T LoadContent<T>(string contentName);
    T TryLoadContent<T>(string contentName);
}

The active loader is held by LoaderManager.Self.ContentLoader. Each runtime (MonoGame, Raylib, and so on) installs a default loader during initialization. To customize loading, assign your own implementation to that property. This is the same property and the same IContentLoader interface on every backend, so the approach is identical across MonoGame, KNI, FNA, and Raylib.

Wrapping the Built-in Loader

The cleanest approach is to wrap the built-in loader: intercept only the content names you care about, and forward everything else to the default loader. This keeps Gum's normal file loading, and its texture caching, working for all the assets you do not handle yourself.

Wrapping is the only way to build on the built-in loader. Each backend's built-in loader is sealed, and none of its methods are virtual, so you implement IContentLoader yourself and hold the built-in loader as a field rather than inheriting from it.

// Class scope
public class CustomContentLoader : RenderingLibrary.Content.IContentLoader
{
    RenderingLibrary.Content.IContentLoader _defaultLoader;

    public CustomContentLoader(RenderingLibrary.Content.IContentLoader defaultLoader)
    {
        _defaultLoader = defaultLoader;
    }

    public T LoadContent<T>(string contentName)
    {
        // typeof(T) is the standard way to branch in an IContentLoader.
        if (typeof(T) == typeof(Texture2D) &&
            MyAssetSource.TryGetTexture(contentName, out Texture2D texture))
        {
            return (T)(object)texture;
        }

        // Forward everything else so default loading and caching still apply.
        return _defaultLoader.LoadContent<T>(contentName);
    }

    public T TryLoadContent<T>(string contentName)
    {
        if (typeof(T) == typeof(Texture2D) &&
            MyAssetSource.TryGetTexture(contentName, out Texture2D texture))
        {
            return (T)(object)texture;
        }

        return _defaultLoader.TryLoadContent<T>(contentName);
    }
}

LoaderManager.Self.ContentLoader already holds your backend's default loader, which Gum installs during GumService.Default.Initialize. Read that property and pass it to your own loader, then assign your loader back to the same property. Do this after Initialize and before any content loads. If you install earlier, ContentLoader is still null and your wrapper has nothing to fall back to.

// Initialize
var loaderManager = RenderingLibrary.Content.LoaderManager.Self;
loaderManager.ContentLoader = new CustomContentLoader(loaderManager.ContentLoader);

Texture caching lives inside the content loader, not above it. A custom IContentLoader that does not delegate to the built-in loader bypasses Gum's cache (LoaderManager.CacheTextures) entirely, so every load goes straight to your code. Wrapping the built-in loader, as shown above, preserves caching for the names you forward. If your custom source already manages its own assets, that is usually fine, and you simply do not need Gum's cache for those.

What Your Loader Receives

Gum resolves a relative content name against FileManager.RelativeDirectory before it calls your loader, so a SourceFile of atlas.png arrives as a full path such as C:/MyGame/Content/atlas.png. A test like contentName == "atlas.png" never matches. Compare with EndsWith or Contains instead.

Gum also does not check whether the name refers to a real file before calling your loader, so a content name can stand for something that is not a file at all. You are free to invent a name such as cart://atlas.png for content your loader resolves on its own. Gum prefixes an invented name the same way it prefixes any other relative name, which is a second reason to match on part of the name rather than all of it.

Sharing a Texture Your Game Already Loaded

A game that draws its own sprites usually holds textures the UI needs too, such as a shared atlas containing item icons and character portraits. Your loader can return one of those textures directly, so the atlas occupies video memory once instead of twice. Texture2D below is your backend's texture type, so it comes from MonoGame on MonoGame and from Raylib_cs on Raylib.

// Class scope
public class AtlasContentLoader : RenderingLibrary.Content.IContentLoader
{
    RenderingLibrary.Content.IContentLoader _defaultLoader;

    public AtlasContentLoader(RenderingLibrary.Content.IContentLoader defaultLoader)
    {
        _defaultLoader = defaultLoader;
    }

    public T LoadContent<T>(string contentName)
    {
        // typeof(T) is the standard way to branch in an IContentLoader.
        if (typeof(T) == typeof(Texture2D) && contentName.EndsWith("atlas.png"))
        {
            return (T)(object)MyRenderer.SharedAtlas;
        }

        return _defaultLoader.LoadContent<T>(contentName);
    }

    public T TryLoadContent<T>(string contentName)
    {
        if (typeof(T) == typeof(Texture2D) && contentName.EndsWith("atlas.png"))
        {
            return (T)(object)MyRenderer.SharedAtlas;
        }

        return _defaultLoader.TryLoadContent<T>(contentName);
    }
}

Install it the same way as any other wrapper, handing it the loader Gum already has:

// Initialize
var loaderManager = RenderingLibrary.Content.LoaderManager.Self;
loaderManager.ContentLoader = new AtlasContentLoader(loaderManager.ContentLoader);

Gum never disposes a texture you return this way, because the texture never enters Gum's cache. Your game keeps ownership of the atlas and decides when to unload it.

Every sprite drawn from the atlas shares one texture, so set each sprite's texture coordinates to pick its own frame out of that texture. See TextureAddress.

Do not put a texture your game owns into Gum's cache with LoaderManager.AddDisposable. Gum disposes everything in that cache when you set CacheTextures to false or call DisposeAndClear, which unloads a texture your game is still drawing. Returning the texture from a loader keeps ownership with your game.

Loading Through the MonoGame Content Pipeline

On the XNA-family backends (MonoGame/KNI/FNA), the built-in ContentLoader also exposes an XnaContentManager property. When set, files referenced without an extension are loaded as content-pipeline (.xnb) assets through that ContentManager. This is an XNA-only convenience; there is no equivalent on Raylib, which has no content pipeline.