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

using System.Collections.Generic;
using System.Linq;
using UnityEditor;
using UnityEditor.AssetImporters;
using UnityEngine;
using UnityEngine.Rendering;

namespace Metamesh
{
    [ScriptedImporter(1, "gph")]
    public class GoldbergPolyhedronImporter : ScriptedImporter
    {
        [SerializeField] float radius = 1;
        [SerializeField, Min(2)] uint subdivision = 2;
        [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();
            mesh.name = "Mesh";

            var builder = new IcosphereBuilder();
            for (var i = 1; i < subdivision; ++i)
            {
                builder = new IcosphereBuilder(builder);
            }

            var vertices = builder.Vertices.Select(v => (Vector3)(v * radius)).ToList();
            var normals = builder.Vertices.Select(v => (Vector3)v).ToList();
            var indices = builder.Indices.ToList();

            ApplyGoldbergTransformation(vertices, normals, indices);

            if (builder.VertexCount > 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;
        }

        private void ApplyGoldbergTransformation(List<Vector3> vertices, List<Vector3> normals, List<int> indices)
        {
            var newVertices = new List<Vector3>();
            var newNormals = new List<Vector3>();
            var newIndices = new List<int>();

            var centers = new Dictionary<int, List<int>>();
            var edges = new HashSet<int>();

            {
                var neighbors = FindNeighbors(0, indices);
                centers.Add(0, neighbors);
                foreach (var i in neighbors)
                {
                    edges.Add(i);
                }
            }

            int inc = 0;
            while (edges.Count + centers.Count < vertices.Count)
            {
                inc++;
                if (inc > 3) break;

                var ccs = FindCenters(edges, indices).Where(c => !centers.ContainsKey(c)).Distinct().ToArray();
                Debug.Log($"while cc in nb: {ccs.Where(c => edges.Contains(c)).Count()}");
                var nbs = ccs.SelectMany(c =>
                {
                    var neighbors = FindNeighbors(c, indices);
                    centers.Add(c, neighbors);
                    return neighbors;
                }).Distinct().Where(i => !edges.Contains(i) && !centers.ContainsKey(i)).ToArray();
                Debug.Log($"while nb in cc: {nbs.Where(c => centers.ContainsKey(c)).Count()}");
                foreach (var i in nbs)
                {
                    edges.Add(i);
                }
                Debug.Log($"centers: {ccs.Count()}/{centers.Count}, edges: {nbs.Count()}/{edges.Count}, vertices: {vertices.Count}");
            }

            Debug.Log($"cc in nb: {centers.Keys.Where(c => edges.Contains(c)).Count()}");
            Debug.Log($"nb in cc: {edges.Where(c => centers.Keys.Contains(c)).Count()}");
            Debug.Log($"missing: {Enumerable.Range(0, vertices.Count).Where(i => !centers.ContainsKey(i)).Where(i => !edges.Contains(i)).Count()}");

            var pentagon = 0;
            var hexagon = 0;
            var start = 0;
            foreach (var i in centers.Keys)
            {
                var neighbors = centers[i].Distinct().ToArray();
                var neighborCount = neighbors.Length;
                if (neighborCount != 5 && neighborCount != 6)
                {
                    Debug.Log($"Unexpected number of neighbors: {neighborCount}");
                    continue;
                }
                if (neighborCount == 5) pentagon++;
                if (neighborCount == 6) hexagon++;
                /*
                var p1 = vertices[neighbors[0]];
                var p2 = vertices[neighbors[2]];
                var p3 = vertices[neighbors[4]];

                var edge1 = p2 - p1;
                var edge2 = p3 - p1;
                var normal = Vector3.Cross(edge1, edge2).normalized;

                var projection = ProjectPointOntoPlane(p1, normal);
                */
                var x = neighbors.Average(i => vertices[i].x);
                var y = neighbors.Average(i => vertices[i].y);
                var z = neighbors.Average(i => vertices[i].z);
                vertices[i] = new Vector3(x, y, z);
                var normal = vertices[i];

                var q = Quaternion.FromToRotation(vertices[i], Vector3.up);
                //var mtx = Matrix4x4.TRS(-vertices[i], q, Vector3.one);
                var mtx = Matrix4x4.TRS(Vector3.zero, q, Vector3.one) * Matrix4x4.TRS(-vertices[i], Quaternion.identity, Vector3.one);
                var sortedNeighbors = neighbors.OrderBy(n =>
                {
                    var direction = mtx.MultiplyPoint(vertices[n]).normalized;
                    var crossProduct = Vector3.Cross(direction, Vector3.up);
                    return Mathf.Atan2(crossProduct.z, crossProduct.x);
                }).ToArray();

                newVertices.Add(vertices[i]);
                newVertices.AddRange(sortedNeighbors.Select(n => vertices[n]));
                newNormals.AddRange(Enumerable.Repeat(normal, neighborCount + 1));

                for (int k = 0; k < neighborCount; ++k)
                {
                    newIndices.Add(start);
                    newIndices.Add(start + (k + 1) % neighborCount);
                    newIndices.Add(start + (k + 0) % neighborCount);
                }
                start += neighborCount + 1;
            }

            vertices.Clear();
            vertices.AddRange(newVertices);
            normals.Clear();
            normals.AddRange(newNormals);
            indices.Clear();
            indices.AddRange(newIndices);

            Debug.Log($"Pentagon: {pentagon}, Hexagon: {hexagon}");
        }

        private Vector3 ProjectPointOntoPlane(Vector3 planePoint, Vector3 planeNormal)
        {
            float distance = Vector3.Dot(planeNormal, Vector3.zero - planePoint);
            Vector3 projection = Vector3.zero - planeNormal * distance;
            return projection;
        }

        private List<int> FindNeighbors(int index, List<int> indices)
        {
            var results = new List<int>();
            for (int i = 0; i < indices.Count; i += 3)
            {
                var i0 = indices[i + 0];
                var i1 = indices[i + 1];
                var i2 = indices[i + 2];
                if (i0 == index) results.AddRange(new[] { i1, i2 });
                if (i1 == index) results.AddRange(new[] { i0, i2 });
                if (i2 == index) results.AddRange(new[] { i0, i1 });
            }
            results = results.Distinct().ToList();
            if (results.Count != 5 && results.Count != 6)
                Debug.Log($"Center#{index}'s neighbors count is {results.Count}");
            return results;
        }

        private List<int> FindCenters(HashSet<int> edges, List<int> indices)
        {
            var results = new List<int>();
            for (int i = 0; i < indices.Count; i += 3)
            {
                var i0 = indices[i + 0];
                var i1 = indices[i + 1];
                var i2 = indices[i + 2];
                var notInEdges = new List<int> { i0, i1, i2 }
                    .Where(v => !edges.Contains(v))
                    .ToList();
                if (notInEdges.Count == 1)
                {
                    var candidate = notInEdges[0];
                    var neighbors = FindNeighbors(candidate, indices);
                    if (neighbors.Count != 5 && neighbors.Count != 6)
                        Debug.Log($"candidate#{candidate}'s neighbors count is {neighbors.Count}");
                    results.Add(candidate);
                }
            }
            return results.Distinct().ToList();
        }
    }
}