uniquake/Assets/Scripts/Modules/BrushModel.cs

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

public class BrushModel
{
    private readonly string name;
    private readonly List<Mesh> meshes = new List<Mesh>();

    // 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>();

    private readonly GameObject rootGameObject;
    private readonly Material debugMaterial;

    public BrushModel(string name)
    {
        this.name = name;

        rootGameObject = new GameObject(name);
        rootGameObject.transform.SetPositionAndRotation(Vector3.zero, Quaternion.identity);
        
        debugMaterial = new Material(Shader.Find("Universal Render Pipeline/Simple Lit"));
    }

    public void ImportMeshData(QModel model)
    {
        var subModels = model.SubModels;
        var surfaces = model.Surfaces;

        for (int modelIdx = 0; modelIdx < subModels.Length; ++modelIdx)
        {
            var modelGO = new GameObject($"SubModel_{modelIdx}");
            modelGO.transform.SetParent(rootGameObject.transform);

            var headNode = subModels[modelIdx].GetHeadNode(model);

            var surfaceGroups = new Dictionary<(IntPtr, int), List<QSurface>>();
            GroupSurfaces(headNode, surfaces, surfaceGroups);

            foreach (var group in surfaceGroups)
            {
                var key = group.Key;
                var groupGO = new GameObject($"T{key.Item1}_L{key.Item2}");
                groupGO.transform.SetParent(modelGO.transform);

                CreateMeshFromSurfaces(group.Value, groupGO.name, groupGO);
            }
        }
    }
    
    public void Dispose()
    {
        foreach (var mesh in meshes)
        {
            UnityEngine.Object.Destroy(mesh);
        }
        
        meshes.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 void CreateMeshFromSurfaces(List<QSurface> surfaces, string key, GameObject parentGO)
    {
        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);
        meshes.Add(mesh);
            
        CreateMeshObject(mesh, parentGO);
    }

    private void CreateMeshObject(Mesh mesh, GameObject parentGO)
    {
        var mf = parentGO.AddComponent<MeshFilter>();
        mf.sharedMesh = mesh;

        var mr = parentGO.AddComponent<MeshRenderer>();
        mr.sharedMaterial = debugMaterial;
        mr.shadowCastingMode = ShadowCastingMode.Off;
        mr.receiveShadows = false;
        mr.lightProbeUsage = LightProbeUsage.Off;
        mr.reflectionProbeUsage = ReflectionProbeUsage.Off;
    }
}