Single threaded meshgen

using System;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Rendering;
using System.Threading.Tasks;
using Unity.Mathematics;
using Unity.Jobs;
using Unity.Collections;
using Unity.Burst;
using UnityEngine.Profiling;
using System.Diagnostics;
using System.Xml.Serialization;

public class MeshGenerator : MonoBehaviour
{
    public static Vector2Int chunkDimensions = new Vector2Int(32, 192);

    public Material material;
    public ComputeShader voxelGridShader;

    public int brushSize;
    public float brushStrength;

    public int lod;
    public int maxLod;

    public int maxChunksProcessing;

    public float surfaceLevel;

    public bool weldedVertices;
    public bool hideMeshOnPlay;
    public bool interpolate;
    public bool stopWatch;


    [Header("Noise Settings")]
    public float heightMultiplier;
    public int curveResolution;
    public AnimationCurve heightCurve;
    public float frequency;
    public float lacunarity;
    public float persistance;
    public int octaves;
    public float density;
    public float warpingStrength;
    public float warpingFrequency;
    public Vector2 offset;

    [Header("")]
    public bool autoUpdate;
    public string executionTime;

    NativeArray<int> nativeTriTable;
    NativeArray<int> nativeCaseToNumPolys;

    Camera cam;

    VoxelGrid voxelGrid;

    List<ChunkData> chunksToProcess;
    int chunksProcessing;

    private void Start()
    {
        Init();

        if (GameObject.Find("Mesh") != null)
        {
            GameObject.Find("Mesh").SetActive(!hideMeshOnPlay);
        }

    }

    private void Update()
    {
        if (Input.GetKeyDown(KeyCode.Space))
        {
            EditorMesh();
        }

        //Limit the number of chunks that can be processed at once, preventing lag spikes
        for (int i = 0; i < chunksToProcess.Count; i++)
        {
            if(chunksProcessing < maxChunksProcessing)
            {
                ProcessChunk(chunksToProcess[i]);
                chunksProcessing++;
                chunksToProcess.RemoveAt(i);
            }
        }
    }

    public GameObject ChunkObject(Vector2 position)
    {
        GameObject chunk = new GameObject("Chunk");
        chunk.AddComponent<MeshFilter>().mesh = ChunkMesh(position, 0);
        chunk.AddComponent<MeshRenderer>().material = material;
        chunk.GetComponent<MeshRenderer>().receiveShadows = false;
        chunk.GetComponent<MeshRenderer>().shadowCastingMode = ShadowCastingMode.Off;

        return chunk;
    }

    public Mesh ChunkMesh(Vector2 position, int lod)
    {
        Mesh mesh = new Mesh();
        mesh.indexFormat = IndexFormat.UInt32;

        lod = lod == 0 ? 1 : lod * 2;

        chunksToProcess.Add(new ChunkData
        {
            mesh = mesh,
            position = position,
            lod = lod
        });

        return mesh;
    }

    public void EditorMesh()
    {
        Init();

        Mesh mesh = ChunkMesh(offset / 10, lod);
        ProcessChunk(chunksToProcess[0]);
        chunksToProcess.Clear();

        if (GameObject.Find("Mesh") == null)
        {
            GameObject obj = new GameObject("Mesh");
            obj.transform.parent = transform;
            obj.AddComponent<MeshFilter>().mesh = mesh;
            obj.AddComponent<MeshRenderer>().material = material;
            obj.AddComponent<MeshCollider>();
        }

        else
        {
            var mf = GameObject.Find("Mesh").GetComponent<MeshFilter>();
            var collider = GameObject.Find("Mesh").GetComponent<MeshCollider>();

            mf.mesh = mesh;
            collider.sharedMesh = null;
            collider.sharedMesh = mesh;
        }
    }

    void Init()
    {
        chunksToProcess = new();
        cam = Camera.main;

        nativeTriTable = new NativeArray<int>(256 * 15, Allocator.Persistent);
        nativeCaseToNumPolys = new NativeArray<int>(256, Allocator.Persistent);


        for (int i = 0; i < Tables.triTable.Length; i++)
        {
            nativeCaseToNumPolys[i] = Tables.caseToNumPolys[i];

            for (int j = 0; j < 15; j++)
            {
                nativeTriTable[(i * 15) + j] = Tables.triTable[i][j];
            }
        }

        voxelGrid = new VoxelGrid(frequency, lacunarity, persistance, octaves, surfaceLevel, density, heightMultiplier, warpingFrequency, warpingStrength, curveResolution, heightCurve, voxelGridShader);
    }

    void ProcessChunk(ChunkData cd)
    {
        //Getting back data from the GPU is slow, so first the voxel grid is requested then
        //whenever the data has reached the CPU the mesh is constructed
        Profiler.BeginSample("Requesting Voxel grid");
        voxelGrid.RequestVoxelGrid(cd.position, cd.lod, out ShaderData shaderData);
        Profiler.EndSample();

        Stopwatch watch = new Stopwatch();
        watch.Start();
        AsyncGPUReadback.Request(shaderData.voxelGridBuffer);
        CompleteReadBack(shaderData, cd.mesh, cd.lod, watch);

        //    AsyncGPUReadback.Request(shaderData.voxelGridBuffer, request =>
        //    {
        //        if (request.hasError)
        //        {
        //            UnityEngine.Debug.LogWarning("GPU readback error detected.");
        //        }
        //        else
        //        {
        //            watch.Stop();
        //            if (stopWatch)
        //                UnityEngine.Debug.Log("Getting voxelGrid took " + watch.ElapsedMilliseconds + " ms");

        //            Profiler.BeginSample("Readback after completion");
        //            NativeArray<float> voxelGrid = request.GetData<float>();
        //            ConstructMesh(voxelGrid, cd.mesh, cd.lod);
        //            Profiler.EndSample();
        //        }
        //    });

        //    //CompleteReadBack(shaderData, cd.mesh, cd.lod, watch);
        //}

    }

    async void CompleteReadBack(ShaderData sd, Mesh mesh, int lod, Stopwatch watch)
    {
        var request = AsyncGPUReadback.Request(sd.voxelGridBuffer);

        // Wait for the request to complete
        while (!request.done)
        {
            await Task.Yield();
        }

        if (request.hasError)
        {
            UnityEngine.Debug.LogWarning("GPU readback error detected.");
        }
        else
        {
            watch.Stop();
            if (stopWatch)
            {
                UnityEngine.Debug.Log("Getting voxelGrid took " + watch.ElapsedMilliseconds + " ms");
            }

            Profiler.BeginSample("Readback after completion");
            //Get voxelGrid after readback is complete
            sd.voxelGridBuffer.Release();
            sd.noiseMap2DBuffer.Release();
            sd.noiseMap2D.Dispose();

            float[] voxelGrid = request.GetData<float>().ToArray();
            ConstructMesh(voxelGrid, mesh, lod);
            Profiler.EndSample();
        }
    }

    async void ConstructMesh(float[] voxelGrid, Mesh mesh, int lod)
    {
        List<Vector3> vertices = new();
        List<int> indices = new();
        Dictionary<Vector3, int> vertDictionary = new();

        MeshData meshData = new MeshData
        {
            vertices = vertices,
            indices = indices,
            vertDictionary = vertDictionary,
            voxelGrid = voxelGrid,
            lod = lod
        };

        //Offloads mesh creation to another thread so the main thread is not halted
        await Task.Run(() =>
        {
            for (int z = 0, i = 0; z < chunkDimensions.x; z += lod)
            {
                for (int y = 0; y < chunkDimensions.y; y += lod)
                {
                    for (int x = 0; x < chunkDimensions.x; x += lod, i++)
                    {
                        AddVertices(i, new Vector3Int(x, y, z), meshData);
                    }
                }
            }
        });

        mesh.vertices = vertices.ToArray();
        mesh.triangles = indices.ToArray();
        mesh.RecalculateNormals();

        chunksProcessing--;
    }

    void AddVertices(int index, Vector3Int pos, MeshData md)
    {
        float[] voxelCornerValues = new float[8];

        for (int i = 0; i < 8; i++)
        {
            voxelCornerValues[i] = md.voxelGrid[(index * 8) + i];
        }

        int triCase = CalculateCase(voxelCornerValues);
        int[] edges = Tables.triTable[triCase];

        for (int j = 0, i = 0; j < Tables.caseToNumPolys[triCase]; j++, i += 3)
        {
            for (int h = 0; h < 3; h++)
            {
                Vector3 vertex = GetEdgePosition(edges[i + (2 - h)], voxelCornerValues, md.lod, pos);

                //Checks for duplicate vertices
                if (md.vertDictionary.TryGetValue(vertex, out int triIndex))
                {
                    md.indices.Add(triIndex);
                }
                else
                {
                    md.vertDictionary.Add(vertex, md.vertices.Count);
                    md.vertices.Add(vertex);
                    md.indices.Add(md.vertices.Count - 1);
                }
            }
        }
    }

    Vector3 GetEdgePosition(int edge, float[] voxelData, int lod, Vector3Int pos)
    {
        int x = pos.x;
        int y = pos.y;
        int z = pos.z;


        switch (edge)
        {
            case 0: return GetInterpolatedEdgePosition(x, y, z, voxelData[0], voxelData[1], 0, 1, 0);
            case 1: return GetInterpolatedEdgePosition(x, y + lod, z, voxelData[1], voxelData[2], 1, 0, 0);
            case 2: return GetInterpolatedEdgePosition(x + lod, y, z, voxelData[3], voxelData[2], 0, 1, 0);
            case 3: return GetInterpolatedEdgePosition(x, y, z, voxelData[0], voxelData[3], 1, 0, 0);

            case 4: return GetInterpolatedEdgePosition(x, y, z + lod, voxelData[4], voxelData[5], 0, 1, 0);
            case 5: return GetInterpolatedEdgePosition(x, y + lod, z + lod, voxelData[5], voxelData[6], 1, 0, 0);
            case 6: return GetInterpolatedEdgePosition(x + lod, y, z + lod, voxelData[7], voxelData[6], 0, 1, 0);
            case 7: return GetInterpolatedEdgePosition(x, y, z + lod, voxelData[4], voxelData[7], 1, 0, 0);

            case 8: return GetInterpolatedEdgePosition(x, y, z, voxelData[0], voxelData[4], 0, 0, 1);
            case 9: return GetInterpolatedEdgePosition(x, y + lod, z, voxelData[1], voxelData[5], 0, 0, 1);
            case 10: return GetInterpolatedEdgePosition(x + lod, y + lod, z, voxelData[2], voxelData[6], 0, 0, 1);
            case 11: return GetInterpolatedEdgePosition(x + lod, y, z, voxelData[3], voxelData[7], 0, 0, 1);

            default: throw new ArgumentOutOfRangeException(nameof(edge), "Invalid edge index: " + edge);
        }
    }
    Vector3 GetInterpolatedEdgePosition(int x, int y, int z, float voxelA, float voxelB, int offsetX, int offsetY, int offsetZ)
    {
        float interpolation = (0 - voxelA) / (voxelB - voxelA);

        return new Vector3(x + offsetX * interpolation, y + offsetY * interpolation, z + offsetZ * interpolation);
    }

    int CalculateCase(float[] voxelData)
    {
        int triCase = 0;

        for (int i = 0; i < 8; i++)
        {
            int bit = voxelData[i] < 0 ? 1 : 0;
            triCase |= bit << i;
        }

        return triCase;
    }

    struct MeshData
    {
        public List<Vector3> vertices;
        public List<int> indices;
        public Dictionary<Vector3, int> vertDictionary;
        public float[] voxelGrid;
        public int lod;
    }

    struct ChunkData
    {
        public Mesh mesh;
        public Vector2 position;
        public int lod;
    }
}

[BurstCompile]
struct MeshJob : IJobParallelFor
{
    [WriteOnly]
    public NativeQueue<Triangle>.ParallelWriter triangles;

    [ReadOnly]
    public NativeArray<float> voxelGrid;

    [ReadOnly]
    public int lod;

    [ReadOnly]
    public int2 chunkDimensions;

    [ReadOnly]
    public bool interpolate;

    [ReadOnly]
    public NativeArray<int> triTable;
    [ReadOnly]
    public NativeArray<int> caseToNumTris;


    public void Execute(int i)
    {
        int z = i / (chunkDimensions.x / lod * chunkDimensions.y / lod) * lod;
        int y = (i / (chunkDimensions.x / lod) * lod) - z / lod * chunkDimensions.y;
        int x = i % (chunkDimensions.x / lod) * lod;

        AddTriangles(i, x, y, z);
    }

    void AddTriangles(int index, int x, int y, int z)
    {
        int triCase = CalculateCase(index);

        int triIndex = 0;

        for (int i = 0; i < caseToNumTris[triCase]; i++)
        {
            int edge0 = triTable[(triCase * 15) + triIndex + 2];
            float3 vertex0 = CalculateVertexPosition(edge0, index, lod, x, y, z);

            int edge1 = triTable[(triCase * 15) + triIndex + 1];
            float3 vertex1 = CalculateVertexPosition(edge1, index, lod, x, y, z);

            int edge2 = triTable[(triCase * 15) + triIndex];
            float3 vertex2 = CalculateVertexPosition(edge2, index, lod, x, y, z);

            triIndex += 3;

            triangles.Enqueue(new Triangle
            {
                vertex0 = vertex0,
                vertex1 = vertex1,
                vertex2 = vertex2
            });
        }
    }

    //Returns vertex position at on of the 12 edges of a cube
    float3 CalculateVertexPosition(int edge, int index, int lod, int x, int y, int z)
    {
        int i = index * 8;

        switch (edge)
        {
            case 0:
                return interpolate ? InterpolatePosition(x, y, z, voxelGrid[i], voxelGrid[i + 1], 0, 1, 0) : new float3(x, y + 1, z);
            case 1:
                return interpolate ? InterpolatePosition(x, y + lod, z, voxelGrid[i + 1], voxelGrid[i + 2], 1, 0, 0) : new float3(x + 1, y + lod, z);
            case 2:
                return interpolate ? InterpolatePosition(x + lod, y, z, voxelGrid[i + 3], voxelGrid[i + 2], 0, 1, 0) : new float3(x + lod, y + 1, z);
            case 3:
                return interpolate ? InterpolatePosition(x, y, z, voxelGrid[i], voxelGrid[i + 3], 1, 0, 0) : new float3(x + 1, y, z);

            case 4:
                return interpolate ? InterpolatePosition(x, y, z + lod, voxelGrid[i + 4], voxelGrid[i + 5], 0, 1, 0) : new float3(x, y + 1, z + lod);
            case 5:
                return interpolate ? InterpolatePosition(x, y + lod, z + lod, voxelGrid[i + 5], voxelGrid[i + 6], 1, 0, 0) : new float3(x + 1, y + lod, z + lod);
            case 6:
                return interpolate ? InterpolatePosition(x + lod, y, z + lod, voxelGrid[i + 7], voxelGrid[i + 6], 0, 1, 0) : new float3(x + lod, y + 1, z + lod);
            case 7:
                return interpolate ? InterpolatePosition(x, y, z + lod, voxelGrid[i + 4], voxelGrid[i + 7], 1, 0, 0) : new float3(x + 1, y, z + lod);

            case 8:
                return interpolate ? InterpolatePosition(x, y, z, voxelGrid[i], voxelGrid[i + 4], 0, 0, 1) : new float3(x, y, z + 1);
            case 9:
                return interpolate ? InterpolatePosition(x, y + lod, z, voxelGrid[i + 1], voxelGrid[i + 5], 0, 0, 1) : new float3(x, y + lod, z + 1);
            case 10:
                return interpolate ? InterpolatePosition(x + lod, y + lod, z, voxelGrid[i + 2], voxelGrid[i + 6], 0, 0, 1) : new float3(x + lod, y + lod, z + 1);
            case 11:
                return interpolate ? InterpolatePosition(x + lod, y, z, voxelGrid[i + 3], voxelGrid[i + 7], 0, 0, 1) : new float3(x + lod, y, z + 1);

            default:
                throw new ArgumentOutOfRangeException(nameof(edge), "Invalid edge index: " + edge);
        }

    }

    public float3 InterpolatePosition(int x, int y, int z, float cornerValue0, float cornerValue1, int offsetX, int offsetY, int offsetZ)
    {
        float interpolation = (0 - cornerValue0) / (cornerValue1 - cornerValue0);

        return new float3(x + offsetX * interpolation, y + offsetY * interpolation, z + offsetZ * interpolation);
    }

    public int CalculateCase(int index)
    {
        int triCase = 0;

        for (int i = 0; i < 8; i++)
        {
            int bit = voxelGrid[(index * 8) + i] < 0 ? 1 : 0;
            triCase |= bit << i;
        }

        return triCase;
    }
}

public struct Triangle
{
    public float3 vertex0;
    public float3 vertex1;
    public float3 vertex2;
}