[Unity]base64エンコードされた画像を表示するサンプル

ButtonConvert.cs

using UnityEngine;
using UnityEngine.UI;
using System.IO;
using System.Text;
using System;

public class ButtonConvert : MonoBehaviour
{
    [SerializeField] private Image image;
    public void OnClick()
    {
        string base64String = ReadFile("gahaha.base64.txt");
        if (string.IsNullOrEmpty(base64String)) {
            return;
        }
        this.image.sprite = SpriteFromBase64(base64String);
    }

    string ReadFile(string fileName)
    {
        // read base64 file
        FileInfo fileInfo = new FileInfo(Application.dataPath + "/Base64/" + fileName);
        string base64String = "";
        try {
            using (StreamReader reader = new StreamReader(fileInfo.OpenRead(), Encoding.UTF8)){
                base64String = reader.ReadToEnd();
            }
        } catch (Exception e){
            Debug.LogError(e);
        }
        return base64String;
    }

    Sprite SpriteFromBase64(string base64String)
    {
        // base64 -> bytes
        byte[] bytes = Convert.FromBase64String(base64String.Split(',')[1]);

        // bytes -> texture
        Texture2D texture2D = new Texture2D(1, 1);
        texture2D.LoadImage(bytes);

        // texture -> sprite
        return Sprite.Create(texture2D, new Rect(0, 0, texture2D.width, texture2D.height), Vector2.zero);
    }
}