uniquake/Assets/Scripts/Support/BrushModel.cs

using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using UnityEngine;
using UnityEngine.Rendering;

public class BrushModel
{
    public string Name { get; }
    
    private readonly List<SubModel> subModels = new List<SubModel>();

    // Reusable temporary data containers
    private readonly List<Vector3> tempVertices = new List<Vector3>();
    private readonly List<Vector2> tempTextureUVs = new List<Vector2>();
    private readonly List<Vector2> tempLightmapUVs = new List<Vector2>();
    private readonly List<ushort> tempIndices = new List<ushort>();

    public BrushModel(string name)
    {
        Name = name;
    }
    
    public int SubModelCount => subModels.Count;

    public SubModel GetSubModel(int index)
    {
        return subModels[index];
    }

    public void ImportMeshData(QModel model)
    {
        var inSubModels = model.SubModels;
        var inSurfaces = model.Surfaces;

        for (int modelIdx = 0; modelIdx < inSubModels.Length; ++modelIdx)
        {
            var subModel = new SubModel();
            subModels.Add(subModel);

            // Traverse the BSP tree and group the surfaces based on their material properties
            var headNode = inSubModels[modelIdx].GetHeadNode(model);
            var surfaceGroups = new Dictionary<(IntPtr, int), List<QSurface>>();
            GroupSurfaces(headNode, inSurfaces, surfaceGroups);

            // Create a single mesh for each group of surfaces
            foreach (var group in surfaceGroups)
            {
                var key = group.Key;
                var mesh = CreateMeshFromSurfaces(group.Value, $"T{key.Item1}_L{key.Item2}");
                
                subModel.AddSurfaceMesh(new SurfaceMesh(mesh, key.Item1, key.Item2));
            }
        }
    }
    
    public void Dispose()
    {
        foreach (var subModel in subModels)
        {
            subModel.Dispose();
        }
        
        subModels.Clear();
    }

    private void GroupSurfaces(QNode node, QSurface[] surfaces, Dictionary<(IntPtr, int), List<QSurface>> surfaceGroups)
    {
        if (node.contents < 0)  // Leaf node
            return;

        for (int surfIdx = 0; surfIdx < node.numSurfaces; ++surfIdx)
        {
            var surface = surfaces[node.firstSurface + surfIdx];
            
            IntPtr texPtr = surface.TextureInfo.texture;
            int lightNum = surface.lightmapTextureNum;
            var key = (texPtr, lightNum);

            if (!surfaceGroups.ContainsKey(key))
                surfaceGroups[key] = new List<QSurface>();
            
            surfaceGroups[key].Add(surface);
        }

        foreach (var childNode in node.Children)
        {
            GroupSurfaces(childNode, surfaces, surfaceGroups);
        }
    }

    private Mesh CreateMeshFromSurfaces(List<QSurface> surfaces, string key)
    {
        tempVertices.Clear();
        tempTextureUVs.Clear();
        tempLightmapUVs.Clear();
        tempIndices.Clear();

        int vertOffset = 0;
        
        for (int surfIdx = 0; surfIdx < surfaces.Count; ++surfIdx)
        {
            foreach (var polyVerts in surfaces[surfIdx].GetPolygons())
            {
                for (int vertIdx = 0; vertIdx < polyVerts.Length; ++vertIdx)
                {
                    tempVertices.Add(polyVerts[vertIdx].position.ToVector3().ToUnity());
                    tempTextureUVs.Add(polyVerts[vertIdx].textureUV.ToVector2());
                    tempLightmapUVs.Add(polyVerts[vertIdx].lightmapUV.ToVector2());
                }
                
                // Reconstruct triangle fan
                for (ushort index = 2; index < polyVerts.Length; ++index)
                {
                    tempIndices.Add((ushort)vertOffset);
                    tempIndices.Add((ushort)(vertOffset + index - 1));
                    tempIndices.Add((ushort)(vertOffset + index));
                }

                vertOffset += polyVerts.Length;
            }
        }
        
        Mesh mesh = new Mesh();
        mesh.name = $"Surfaces_{key}";
        mesh.SetVertices(tempVertices);
        mesh.SetUVs(0, tempTextureUVs);
        mesh.SetUVs(1, tempLightmapUVs);
        mesh.SetIndices(tempIndices, MeshTopology.Triangles, 0);
        mesh.RecalculateNormals();
        mesh.UploadMeshData(true);
        return mesh;
    }

    public class SubModel
    {
        public List<SurfaceMesh> SurfaceMeshes { get; } = new List<SurfaceMesh>();

        public void AddSurfaceMesh(SurfaceMesh surfaceMesh)
        {
            SurfaceMeshes.Add(surfaceMesh);
        }

        public void Dispose()
        {
            foreach (var surfaceMesh in SurfaceMeshes)
            {
                surfaceMesh.Dispose();
            }
        }
    }
    
    public class SurfaceMesh
    {
        public Mesh Mesh { get; }
        public QTexture Texture { get; }
        public int Lightmap { get; }

        public SurfaceMesh(Mesh mesh, IntPtr texturePtr, int lightmap)
        {
            Mesh = mesh;
            Texture = Marshal.PtrToStructure<QTexture>(texturePtr);
            Lightmap = lightmap;
        }

        public void Dispose()
        {
            UnityEngine.Object.Destroy(Mesh);
        }
    }
}