Test-Planet/Assets/Scripts/Editor/GoldbergPolyhedronImporter.cs

using System.Collections.Generic;
using System.Linq;
using UnityEditor;
using UnityEditor.AssetImporters;
using UnityEngine;
using UnityEngine.Rendering;
using static Metamesh.GoldbergBuilder;

namespace Metamesh
{
    [ScriptedImporter(1, "gph")]
    public class GoldbergPolyhedronImporter : ScriptedImporter
    {
        [SerializeField] float radius = 1;
        [SerializeField, Min(2)] uint subdivision = 2;
        [SerializeField, Min(1)] int m = 1;
        [SerializeField, Min(0)] int n = 0;

        [SerializeField] bool generateLightmapUVs = false;
        [SerializeField] bool readWriteMeshes = false;

        [MenuItem("Assets/Create/GoldbergPolyhedron")]
        public static void CreateNewAsset() => ProjectWindowUtil.CreateAssetWithContent("New GoldbergPolyhedron.gph", "");

        public override void OnImportAsset(AssetImportContext context)
        {
            var gameObject = new GameObject();
            var mesh = ImportAsMesh();

            var meshFilter = gameObject.AddComponent<MeshFilter>();
            meshFilter.sharedMesh = mesh;

            var pipelineAsset = GraphicsSettings.currentRenderPipeline;
            var baseMaterial = pipelineAsset ? pipelineAsset.defaultMaterial : AssetDatabase.GetBuiltinExtraResource<Material>("Default-Diffuse.mat");

            var meshRenderer = gameObject.AddComponent<MeshRenderer>();
            meshRenderer.sharedMaterial = baseMaterial;

            context.AddObjectToAsset("prefab", gameObject);
            if (mesh != null) context.AddObjectToAsset("mesh", mesh);

            context.SetMainObject(gameObject);
        }

        private Mesh ImportAsMesh()
        {
            var mesh = new Mesh
            {
                name = "Mesh"
            };

            var builder = new GoldbergBuilder();
            var options = new GoldbergCreationOption()
            {
                m = m,
                n = n,
            };
            var data = builder.CreateGoldberg(options);
            var vertices = data.vertices;
            var normals = data.normals;
            var indices = data.indices;

            if (vertices.Count > 65535) mesh.indexFormat = IndexFormat.UInt32;
            mesh.SetVertices(vertices);
            mesh.SetNormals(normals);
            mesh.SetIndices(indices, MeshTopology.Triangles, 0);

            mesh.RecalculateBounds();
            mesh.RecalculateNormals();
            if (generateLightmapUVs) Unwrapping.GenerateSecondaryUVSet(mesh);
            mesh.UploadMeshData(!readWriteMeshes);

            return mesh;
        }
    }
}