uniquake/Assets/Scripts/Modules/BrushModel.cs

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

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

        for (int modelIdx = 0; modelIdx < subModels.Length; ++modelIdx)
        {
            var headNode = subModels[modelIdx].GetHeadNode(model);
            CreateNodeMeshes(headNode, surfaces);
        }

        // DEBUG
        var go = new GameObject(name);
        var mat = new Material(Shader.Find("Universal Render Pipeline/Simple Lit"));
        
        for (int i = 0; i < meshes.Count; ++i)
        {
            var mesh = meshes[i];

            var meshGO = new GameObject($"Surface_{i}");
            meshGO.transform.SetParent(go.transform);
            
            var mf = meshGO.AddComponent<MeshFilter>();
            mf.sharedMesh = mesh;
            
            var mr = meshGO.AddComponent<MeshRenderer>();
            mr.sharedMaterial = mat;
            mr.shadowCastingMode = ShadowCastingMode.Off;
            mr.receiveShadows = false;
            mr.lightProbeUsage = LightProbeUsage.Off;
            mr.reflectionProbeUsage = ReflectionProbeUsage.Off;
        }
        
        go.transform.SetPositionAndRotation(Vector3.zero, Quaternion.identity);
    }

    private void CreateNodeMeshes(QNode node, QSurface[] surfaces)
    {
        if (node.contents < 0)  // Leaf node
            return;
        
        CreateSurfaceMeshes(node, surfaces);

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

    private void CreateSurfaceMeshes(QNode node, QSurface[] surfaces)
    {
        for (int surfIdx = 0; surfIdx < node.numSurfaces; ++surfIdx)
        {
            var surface = surfaces[node.firstSurface + surfIdx];
                
            foreach (var polyVerts in surface.GetPolygons())
            {
                tempVertices.Clear();
                tempTextureUVs.Clear();
                tempLightmapUVs.Clear();
                tempIndices.Clear();

                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(0);
                    tempIndices.Add((ushort) (index - 1));
                    tempIndices.Add(index);
                }

                Mesh mesh = new Mesh();
                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);
            }

            var texNum = surface.TextureInfo.Texture.TextureNum;
        }
    }
}