Non-blocking loading and copying of large Texture2D’s in C# for Unity

Introduction

Loading and copying large Texture2D assets in Unity can be a performance bottleneck, especially on mobile devices or with limited hardware. Blocking operations can cause noticeable frame drops and make your game feel unresponsive. This article will guide you through techniques for achieving non-blocking loading and copying of large textures in C# for Unity.

Understanding the Problem

Unity’s default Texture2D loading and copying methods are synchronous, meaning the main thread waits until the operation completes before proceeding. This can cause the game to freeze or become unresponsive if the texture is large.

Causes of Blocking:

• Texture Loading: Reading the texture data from disk or memory.
• Texture Decoding: Converting the texture data into a format usable by the GPU.
• Texture Copying: Creating a new Texture2D object and copying data from the original texture.

Non-Blocking Techniques

To prevent blocking, we’ll leverage Unity’s asynchronous capabilities and manage the process in separate threads.

1. Asynchronous Loading with `Texture2D.LoadImageAsync`

This is the primary method for non-blocking texture loading in Unity. It allows you to load a texture from a file or byte array asynchronously.

Example

using UnityEngine;
using System.Collections;

public class AsyncTextureLoading : MonoBehaviour {

    public Texture2D largeTexture;

    void Start() {
        StartCoroutine(LoadTextureAsync());
    }

    IEnumerator LoadTextureAsync() {
        // Load the texture asynchronously
        var request = largeTexture.LoadImageAsync(System.IO.File.ReadAllBytes("path/to/your/texture.png"));

        // Wait for the request to complete
        yield return new WaitUntil(() => request.isDone);

        // Apply the loaded texture to a game object
        GetComponent().material.mainTexture = largeTexture;
    }
}

2. Asynchronous Texture Copying with `Texture2D.GetRawTextureData` and `Texture2D.SetPixelData`

For more complex scenarios, you might need to copy the texture data instead of directly loading a new texture. This can be achieved using the following steps:

1. Get Raw Texture Data: Retrieve the texture data in byte array format using `Texture2D.GetRawTextureData`.
2. Create a New Texture: Instantiate a new Texture2D object with the desired dimensions and format.
3. Set Pixel Data: Copy the byte data to the new texture using `Texture2D.SetPixelData`. Ensure to use non-blocking `SetPixelData` variants.
4. Apply and Update: Call `Apply` on the new texture to update its contents on the GPU.

Example

using UnityEngine;
using System.Collections;

public class AsyncTextureCopying : MonoBehaviour {

    public Texture2D largeTexture;

    void Start() {
        StartCoroutine(CopyTextureAsync());
    }

    IEnumerator CopyTextureAsync() {
        // Get raw texture data
        var data = largeTexture.GetRawTextureData();

        // Create a new texture with the same dimensions and format
        var newTexture = new Texture2D(largeTexture.width, largeTexture.height, largeTexture.format, false);

        // Copy data to the new texture asynchronously
        newTexture.SetPixelData(data, 0);
        yield return new WaitForEndOfFrame(); // Ensure update is completed
        newTexture.Apply(false);

        // Use the copied texture
        GetComponent().material.mainTexture = newTexture;
    }
}

Performance Optimization

Consider these additional optimization techniques for further enhancing performance:

• Texture Compression: Compress large textures using formats like ETC2 or ASTC to reduce memory usage and improve loading times.
• Mipmaps: Generate mipmaps for large textures to accelerate rendering and improve visual quality at different distances.
• Texture Streaming: Implement texture streaming to load textures on demand only when needed, reducing initial loading times.
• Texture Atlas: Combine multiple smaller textures into a single atlas for better performance and reduced draw calls.

Comparison Table

| Technique | Blocking | Advantages | Disadvantages |
|—|—|—|—|
| `Texture2D.LoadImageAsync` | No | Simple, efficient for loading from files | Limited to loading from files or byte arrays |
| `Texture2D.GetRawTextureData` + `Texture2D.SetPixelData` | No | Flexible for copying and manipulating texture data | More complex, requires manual management |

Conclusion

By implementing non-blocking texture loading and copying techniques, you can significantly improve the performance of your Unity games, especially when dealing with large textures. Use `Texture2D.LoadImageAsync` for simple asynchronous loading and the combination of `GetRawTextureData` and `SetPixelData` for more advanced operations. Remember to apply optimization techniques like compression and mipmaps to further boost performance.