using System.IO;
using UnityEditor;
using UnityEngine;

public class ExampleEditorScript : MonoBehaviour
{
    [MenuItem("Tools/PalletteTexture")]
    static void CreateTexture3D()
    {
        int size = 256;
        int sizeSub = size - 1;
        TextureFormat format = TextureFormat.RGBA32;
        TextureWrapMode wrapMode = TextureWrapMode.Clamp;

        Texture2D texture = new Texture2D(size, size, format, false);
        texture.wrapMode = wrapMode;

        var size2D = size * size;
        Color[] colors = new Color[size2D];
        for (int i = 0; i < size2D; i++)
        {
            colors[i] = Color.clear;
        }
        var image = Resources.Load<Texture2D>("Pallette/palette");
        var pixels = image.GetPixels(); //must be size
        for (int i = 0; i < size; i++)
        {
            var color = pixels[i];
            var x = color.r * sizeSub;
            var y = color.b * sizeSub;
            var cood = (int)(x * size + y);
            var value = i * 1f / size;
            colors[cood] = new Color(value, value, value, 1);
        }

        texture.SetPixels(colors);
        texture.Apply();
        byte[] bytes = texture.EncodeToPNG();
        var dirPath = Application.dataPath + "/Resources/Pallette/";
        File.WriteAllBytes(dirPath + "PalletteTex.png", bytes);
    }
}