Does Unity Build Unused Assets? Untangling the Truth About Project Size

The short answer is no, Unity doesn’t typically build unused assets into your final game. However, the reality is nuanced, and understanding how Unity handles assets during the build process is crucial for optimizing your game’s size and performance. Unity employs a process called stripping during the build, which aims to remove any assets that aren’t referenced or actively used in your scenes, scripts, or other connected asset dependencies.

How Unity’s Stripping Process Works

Unity’s build pipeline isn’t just a simple copy-paste operation. It intelligently analyzes your project to identify what’s truly needed for the final product. Here’s a breakdown of how it works:

• Dependency Analysis: The build process begins by examining all your scenes, scripts, and assets to understand their dependencies. It essentially creates a map of what connects to what. For example, if a scene contains a GameObject that uses a particular material, that material, along with its textures and shader, are marked as “in use.”
• Code Stripping: Unity also analyzes your C# code, specifically looking for code paths that are never executed. If a section of code references an asset, but that code is never called during gameplay, the asset might be considered unused. This is where things can get tricky, and proper coding practices become essential (more on this later).
• Asset Stripping: Based on the dependency analysis and code stripping, Unity identifies which assets are considered “unused.” These assets are then excluded from the final build. This dramatically reduces the size of your game, especially in projects with many assets.
• Compression and Optimization: Finally, Unity compresses and optimizes the remaining assets to further reduce the build size. Techniques like texture compression, mesh optimization, and audio encoding are employed to ensure the smallest possible footprint.

The Caveats: When Unused Assets Can Sneak In

While Unity strives to strip unused assets, there are situations where they might still end up in your build:

• Dynamic Loading at Runtime: If you are loading assets dynamically using Resources.Load, AssetBundles, or the Addressable Asset System, Unity might not be able to determine whether those assets are truly unused during the build process. You might need to manually manage the loading and unloading of these assets to ensure they don’t unnecessarily inflate your build size.
• Reflection and String-Based References: If your code relies heavily on reflection or string-based references to access assets (e.g., loading a texture by its name stored in a string), Unity’s dependency analysis might fail to detect these dependencies. As a result, the assets might be included even if they are never explicitly used.
• Editor Scripts and Tools: Assets used solely by editor scripts or custom tools aren’t automatically excluded. If those assets aren’t also used during gameplay, they’ll unnecessarily increase the size of your final game.
• Accidental References: Sometimes, you might inadvertently create references to assets that are no longer needed. For example, a script might contain a public variable that references a texture, but the script no longer uses that variable. These accidental references can prevent Unity from stripping the asset.

Best Practices for Asset Management and Build Optimization

To ensure your Unity build is as lean as possible, follow these best practices:

• Use AssetBundles or Addressables: For dynamically loaded content, AssetBundles or the Addressable Asset System provide more control over asset management and allow you to download and unload assets on demand. This can significantly reduce the initial build size.
• Avoid String-Based Asset Loading: Instead of loading assets by name using strings, use direct references whenever possible. Drag and drop assets directly into your scripts or scenes to create explicit dependencies.
• Implement a Consistent Naming Convention: A well-organized naming convention for your assets makes it easier to identify and manage them, reducing the risk of accidental references or unused assets.
• Regularly Clean Up Your Project: Periodically review your project and remove any assets that are no longer needed. Be sure to check for unused scenes, scripts, and prefabs.
• Use Tools to Find Unused Assets: Several Asset Store tools, like UnityAssetCleaner, can help you identify unused assets in your project. These tools analyze your project and provide a list of assets that are not referenced by any scenes, scripts, or other assets.
• Profile Your Build: Use Unity’s Profiler to identify any performance bottlenecks or areas where your build size can be reduced. Pay attention to the memory usage of your assets and optimize them accordingly.
• Optimize Textures and Meshes: Use appropriate texture compression formats and optimize your meshes to reduce their size. Tools like Mesh Baker can combine multiple meshes into a single mesh, reducing the number of draw calls and improving performance.
• Leverage Scriptable Render Pipeline (SRP): If you are using the Universal Render Pipeline (URP) or the High Definition Render Pipeline (HDRP), ensure that you are only including the features and shaders that you actually need. Unnecessary features can significantly increase the size of your build.
• Version Control is Key: Utilize a robust version control system like Git to track changes to your project and easily revert to previous versions if needed. This helps prevent accidental deletions or corruption of assets.

The Importance of Understanding Unity’s Asset Management

In the world of game development, especially when working in Unity, understanding how the engine manages assets is paramount to creating efficient and optimized games. By knowing what Unity does automatically, and understanding the situations that might cause problems, developers can take proactive steps to ensure their final product is streamlined and performs at its best. Remember that GamesLearningSociety.org offers numerous resources for developers to grow their skills.

The knowledge of how to correctly use the Asset Store assets is also important.

Frequently Asked Questions (FAQs)

Here are some frequently asked questions about how Unity handles assets during the build process:

1. Is it true that Unity’s build process automatically removes unused assets?

Yes, Unity generally strips out unused assets during the build process through its dependency analysis and code stripping mechanisms. However, certain situations like dynamic loading or reflection can prevent this from working perfectly.

2. What are AssetBundles, and how do they help with build size?

AssetBundles are archives containing assets that can be downloaded and loaded at runtime. By splitting your game into smaller bundles, you can reduce the initial download size and stream content as needed.

3. What is the Addressable Asset System in Unity?

The Addressable Asset System is a more advanced asset management system that provides a flexible way to load and manage assets by address (string-based key). It offers features like content delivery network (CDN) support and remote updates.

4. How do I use AssetBundles to optimize my build size?

First, you need to create AssetBundles from your assets in the Unity editor. Then, you can upload these bundles to a server and download them at runtime using Unity’s UnityWebRequest class or the Addressable Asset System.

5. Can reflection cause unused assets to be included in my build?

Yes, if your code uses reflection to access assets, Unity might not be able to detect these dependencies, leading to unused assets being included. Try to minimize the use of reflection.

6. What is texture compression, and why is it important?

Texture compression reduces the size of texture files, which can significantly impact your build size and memory usage. Unity supports various texture compression formats like ETC2, ASTC, and DXT.

7. How do I optimize meshes in Unity?

You can optimize meshes by reducing the number of vertices and triangles, simplifying the mesh geometry, and removing unnecessary details. Tools like ProBuilder or third-party mesh optimization plugins can help with this.

8. What is a draw call, and why should I minimize them?

A draw call is a request from the CPU to the GPU to render a specific object. Too many draw calls can bottleneck your performance. Techniques like mesh combining and GPU instancing can help reduce the number of draw calls.

9. What are Scriptable Render Pipelines (SRP), and how do they impact build size?

Scriptable Render Pipelines (SRP) like URP and HDRP allow you to customize the rendering pipeline in Unity. By only including the features you need, you can reduce the size of your build and improve performance.

10. How can I find unused assets in my Unity project?

You can manually search for unused assets by examining your scenes, scripts, and prefabs. Alternatively, you can use Asset Store tools like UnityAssetCleaner to automate this process.

11. What’s the difference between Resources.Load and the Addressable Asset System?

Resources.Load is a simple way to load assets from the Resources folder, but it can lead to larger build sizes and less control over asset management. The Addressable Asset System provides a more flexible and scalable solution for managing assets.

12. How does code stripping work in Unity?

Unity’s code stripping process analyzes your C# code to identify code paths that are never executed. Any code that references an asset but is never called will be considered unused, and the associated asset may be stripped from the build.

13. Are free assets from the Unity Asset Store truly free to use commercially?

Yes, generally, free assets from the Unity Asset Store can be used commercially on a royalty-free basis. However, always review the license agreement for each asset to ensure compliance, as the specific terms can vary. You can find resources and support through the Games Learning Society at https://www.gameslearningsociety.org/.

14. What happens if I accidentally delete an asset in Unity?

If you have a version control system like Git, you can easily revert to a previous version and recover the deleted asset. Otherwise, you might have to recreate the asset from scratch.

15. How do I manage large textures in Unity to minimize memory usage?

Use appropriate texture compression formats, reduce the texture resolution, and enable mipmaps. You can also use texture streaming to load textures on demand.