Unity Texture2D Custom Mipmap Importer

CustomMipImporter.cs

using UnityEngine;
using UnityEditor;
using System.IO;

using UnityEditor.AssetImporters;

[ScriptedImporter(2026_04_27, kFileExtension)]
public class CustomMipImporter : ScriptedImporter
{
    public Texture2D[] m_Mips;
    public TextureFormat m_Format = TextureFormat.BC7;

    private const string kFileExtension = "tex2dmips";

    public override void OnImportAsset(AssetImportContext ctx)
    {
        foreach (var tex in m_Mips)
        {
            if (tex != null)
            {
                var path = AssetDatabase.GetAssetPath(tex);
                ctx.DependsOnArtifact(path);
            }
        }
        
        var width = m_Mips.Length > 0 ? m_Mips[0].width : 64;
        var height = m_Mips.Length > 0 ? m_Mips[0].height : 64;
        var format = TextureFormat.RGBA32;
        
        Texture2D result = new Texture2D(width, height, format, m_Mips.Length, false);
        for (var mip = 0; mip < m_Mips.Length; ++mip)
        {
            Color32[] pixels = m_Mips[mip].GetPixels32();
            result.SetPixels32(pixels, mip);
        }

        result.Apply(false, false);
        EditorUtility.CompressTexture(result, m_Format, TextureCompressionQuality.Normal);
        ctx.AddObjectToAsset("Tex2DMips", result);
        ctx.SetMainObject(result);
    }

    [MenuItem("Assets/Create/Rendering/Tex2D Custom Mips")]
    static void CreateCustomMipsMenuItem()
    {
        string folder = "Assets";
        foreach (Object obj in Selection.GetFiltered(typeof(Object), SelectionMode.Assets))
        {
            folder = AssetDatabase.GetAssetPath(obj);
            if (!string.IsNullOrEmpty(folder) && File.Exists(folder))
            {
                folder = Path.GetDirectoryName(folder);
                break;
            }
        }
        folder = folder.Replace("\\", "/");
        if (folder.Length > 0 && folder[^1] != '/')
            folder += "/";
        if (string.IsNullOrEmpty(folder))
            folder = "Assets/";

        var fileName = $"New Tex2DCustomMips.{kFileExtension}";
        folder = AssetDatabase.GenerateUniqueAssetPath(folder + fileName);
        ProjectWindowUtil.CreateAssetWithContent(folder, "This is a CustomMips Asset");
    }
}