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>();

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

    public void ImportMeshData(QModel model, QSurface[] surfaces)
    {
        List<Vector3> vertices = new List<Vector3>();
        List<Vector2> textureUVs = new List<Vector2>();
        List<Vector2> lightmapUVs = new List<Vector2>();
        List<ushort> indices = new List<ushort>();
        
        for (int surfIdx = 0; surfIdx < surfaces.Length; ++surfIdx)
        {
            foreach (var polyVerts in surfaces[surfIdx].GetPolygons())
            {
                vertices.Clear();
                textureUVs.Clear();
                lightmapUVs.Clear();
                indices.Clear();

                for (int vertIdx = 0; vertIdx < polyVerts.Length; ++vertIdx)
                {
                    vertices.Add(polyVerts[vertIdx].position.ToVector3());
                    textureUVs.Add(polyVerts[vertIdx].textureUV.ToVector2());
                    lightmapUVs.Add(polyVerts[vertIdx].lightmapUV.ToVector2());
                }

                // Reconstruct triangle fan (in reverse order)
                for (ushort index = 2; index < polyVerts.Length; ++index)
                {
                    indices.Add(index);
                    indices.Add((ushort)(index - 1));
                    indices.Add(0);
                }
                
                Mesh mesh = new Mesh();
                mesh.SetVertices(vertices);
                mesh.SetUVs(0, textureUVs);
                mesh.SetUVs(1, lightmapUVs);
                mesh.SetIndices(indices, MeshTopology.Triangles, 0);
                mesh.RecalculateNormals();
                mesh.UploadMeshData(true);
                meshes.Add(mesh);
            }

            var texNum = surfaces[surfIdx].TextureInfo.Texture.TextureNum;
        }
        
        // 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.Euler(-90, 90, 0));
    }
}