Terrain layer color editor

TerrainColorImporter.cs

//Copy-paste me in a script file named "TerrainColorImporter" and place it in any folder called "Editor"

using UnityEngine;
using UnityEditor;
using UnityEditor.AssetImporters;
using System.IO;

[ScriptedImporter(1, FILE_EXTENSION)]
public class TerrainColorImporter : ScriptedImporter
{
    private const string FILE_EXTENSION = "terraincolor";
    
    public Color color = Color.white;
    [Range(0f,1f)]
    public float smoothness = 0.15f;
    
    private const int textureSize = 4;

    private Texture2D _icon;
    private Texture2D icon
    {
        get
        {
            if(_icon == null) _icon = EditorGUIUtility.IconContent("PreTextureRGB").image as Texture2D;
            return _icon;
        }
    }
    public override void OnImportAsset(AssetImportContext ctx)
    {
        Texture2D texture = new Texture2D(textureSize, textureSize, TextureFormat.RGBA32, true);
        
        Color[] pixels = new Color[textureSize * textureSize];
        for (int i = 0; i < pixels.Length; i++)
        {
            pixels[i] = color;
            pixels[i].a = smoothness;
        }
        texture.SetPixels(pixels);
        texture.name = this.name + " Color";
        texture.Apply();
        
        TerrainLayer terrainLayer = new TerrainLayer
        {
            diffuseTexture = texture,
            tileSize = Vector2.one,
            name = this.name + "_Layer",
            smoothness = smoothness,
        };
        
        ctx.AddObjectToAsset("TerrainLayer", terrainLayer, icon);
        ctx.AddObjectToAsset("MainTexture", texture);
        ctx.SetMainObject(terrainLayer);
    }
    
    [MenuItem("Assets/Create/Terrain/Color Layer", false, 2000)]
    public static void CreateColorTextureFile()
    {
        ProjectWindowUtil.CreateAssetWithContent($"New Terrain Color.{FILE_EXTENSION}", "");
    }
    
    //Handles correct behaviour when double-clicking a .watermesh asset assigned to a field
    //Otherwise the OS prompts to open it
    [UnityEditor.Callbacks.OnOpenAsset]
    public static bool OnOpenAsset(int instanceID, int line)
    {
        Object target = EditorUtility.InstanceIDToObject(instanceID);

        if (target is Mesh)
        {
            var path = AssetDatabase.GetAssetPath(instanceID);
                
            if (Path.GetExtension(path) != "." + FILE_EXTENSION) return false;

            Selection.activeObject = target;
            return true;
        }
            
        return false;
    }
}

[CustomEditor(typeof(TerrainColorImporter))]
public class TerrainColorImporterEditor : ScriptedImporterEditor
{
    public override void OnInspectorGUI()
    {
        EditorGUI.BeginChangeCheck();
        
        base.OnInspectorGUI();

        if (EditorGUI.EndChangeCheck() && HasModified())
        {
            #if UNITY_2022_2_OR_NEWER
            this.SaveChanges();
            #else
            this.ApplyAndImport();
            #endif
        }
        
        EditorGUILayout.Space();
        //EditorGUILayout.LabelField("- Staggart Creations -", EditorStyles.centeredGreyMiniLabel);
    }
}