How would I save texture along with other data in binary file in Unity?

Question

So I have a save method that can save data to a binary file and another function that saves just the texture. I would like to save both of them in a same file. I guess I would need to create a serialization surrogate for the Texture2D (I did this for some other types like Vector3 and Quaternion) but I can't find anywhere how would I do it for texture. I am currently saving texture like byte array and I guess that could help but I am not sure how to add it to other data.

Here is my code for saving the data:

public static bool Save(string fileLocation, string saveFilename,object saveData)
{
    BinaryFormatter formatter = GetBinaryFormater();

    if (!Directory.Exists(fileLocation))
    {
        Directory.CreateDirectory(fileLocation);
    }

    string path = fileLocation + "/" + saveFilename + ".save";
    FileStream file = File.Create(path);
    formatter.Serialize(file, saveData);
    file.Close();

    Debug.Log("Save to: " + path);
    return true;
}

And here is the one for the texture:

public static bool SaveTexture(string fileLocation, string filename, Texture2D textureToSave)
{
    if (!Directory.Exists(fileLocation))
    {
        Directory.CreateDirectory(fileLocation);
    }

    byte[] byteArray = textureToSave.EncodeToJPG();
    string savedFilename = fileLocation + "/" + filename + ".jpg";

    File.WriteAllBytes(savedFilename, byteArray);
    Debug.Log("File saved at: " + savedFilename);

    return true;
}

Philipp · Accepted Answer · 2022-08-24 07:35:35Z

One problem with binary file formats is that it is difficult to tell where one block of data ends and another block starts.

A common method is to prefix every variable-length block of data with an integer which states its length in bytes, and then read that many bytes. So your file would consist of:

4 bytes stating the length of the binary data in bytes
The data
4 bytes stating the length of the texture in byte
The texture

An alternative approach is to begin the file with a fixed length index which lists all the file positions where the chunks start and end. This has the advantage that you can load individual chunks by seeking within the file. If you only need a small part of the file, for example for a preview image, you don't need to process the whole file from start to end.

You can get the length in byte created by a BinaryFormatter by not passing it a FileStream but a MemoryStream. You can then check the number of bytes with the .Length property and you can write it to a file using memoryStream.CopyTo(fileStream);.

Untested code, but it should kind of work like this:

// serialize the saveData object to memory
MemoryStream memory = new MemoryStream();
formatter.Serialize(memory, saveData);
memory.Seek(0, SeekOrigin.Begin);
// Create the file
FileStream file = File.Create(path);
// write the length of the save data
file.Write(BitConverter.GetBytes(memory.Length)); 
// write the actual save data
memory.CopyTo(file);
// write the length of the texture
file.Write(BitConverter.GetBytes(byteArray.Length)); 
// write the texture
file.Write(byteArray, 0, byteArray.Length);
// close the file
file.Close();

For reading the file, you can load individual bytes from a FileStream using the Read method. In order to convert 4 bytes into integers, you could again use the BitConverter with the BitConverter.ToInt32 method, or you might consider to wrap the FileStream in a BinaryReader, because that allows you to use methods like .ReadInt.

I can try it out if I understand it right. IS there another file format that would be more suitable for these things? — Ivan
– Ivan, Commented Aug 23, 2022 at 12:57
Can you mention a few I usually only used json and binary for saving my files. — Ivan
– Ivan, Commented Aug 23, 2022 at 13:01
@Ivan zip is fine. Or if you want to store binary datasets in JSON, then you can encode them as BASE64 and store them as strings in a JSON object. — Philipp
– Philipp, Commented Aug 23, 2022 at 13:03
Careful, BinaryFormatter is insecure and can be used to execute arbitrary code. Microsoft says apps should stop using it. This might not seem like a big deal; your game might not have any sensitive/secret stuff in it. But if an attacker can convince one of your players to load a malicious save file ("want a save with 100% completion and the ultimate weapon unlocked? Here you go!") then they can potentially use this pathway to install malware on the player's computer, or leak their private data. — DMGregory
– DMGregory ♦, Commented Aug 16, 2023 at 9:30

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