doom-dm/Engine/Asset/Mesh/Loader/ObjMeshLoader.cs

using System.Globalization;
using OpenTK.Mathematics;

namespace Engine.Asset.Mesh.Loader;

public class ObjMeshLoader : IMeshLoader
{
    private static readonly ObjMeshLoader Instance = new();

    public static Mesh Load(string path, MeshLoaderParameters parameters = MeshLoaderParameters.Default)
        => Instance.LoadMesh(path, parameters);

    public Mesh LoadMesh(string path, MeshLoaderParameters parameters = MeshLoaderParameters.Default)
    {
        var mesh = new Mesh();

        var tempVertices = new List<Vector3>();
        var tempNormals = new List<Vector3>();
        var tempUVs = new List<Vector2>();
        var index = 0u;

        var loadNormals = parameters.HasFlag(MeshLoaderParameters.LoadNormals);
        var loadUVs = parameters.HasFlag(MeshLoaderParameters.LoadUVs);

        using var reader = new StreamReader(path);
        while (reader.ReadLine() is { } line)
        {
            var parts = line.Split(' ', StringSplitOptions.RemoveEmptyEntries);

            if (parts.Length == 0 || parts[0].StartsWith('#'))
                continue;

            switch (parts[0])
            {
                case "v":
                    tempVertices.Add(new Vector3(
                        float.Parse(parts[1], CultureInfo.InvariantCulture),
                        float.Parse(parts[2], CultureInfo.InvariantCulture),
                        float.Parse(parts[3], CultureInfo.InvariantCulture)
                    ));
                    break;

                case "vt" when loadUVs:
                    tempUVs.Add(new Vector2(
                        float.Parse(parts[1], CultureInfo.InvariantCulture),
                        float.Parse(parts[2], CultureInfo.InvariantCulture)
                    ));
                    break;

                case "vn" when loadNormals:
                    tempNormals.Add(new Vector3(
                        float.Parse(parts[1], CultureInfo.InvariantCulture),
                        float.Parse(parts[2], CultureInfo.InvariantCulture),
                        float.Parse(parts[3], CultureInfo.InvariantCulture)
                    ));
                    break;

                case "f":
                    for (var i = 1; i <= 3; i++)
                    {
                        var faceComponents = parts[i].Split('/');
                        var meshVertex = new Mesh.Vertex
                        {
                            Position = tempVertices[int.Parse(faceComponents[0]) - 1]
                        };

                        if (loadUVs && faceComponents.Length > 1 && faceComponents[1] != "")
                        {
                            meshVertex.Uv = tempUVs[int.Parse(faceComponents[1]) - 1];
                        }

                        if (loadNormals && faceComponents.Length > 2 && faceComponents[2] != "")
                        {
                            meshVertex.Normal = tempNormals[int.Parse(faceComponents[2]) - 1];
                        }

                        mesh.VerticesInternal.Add(meshVertex);
                        mesh.IndicesInternal.Add(index++);
                    }

                    break;
            }
        }

        if (parameters.HasFlag(MeshLoaderParameters.Optimize))
            mesh = IMeshLoader.Optimize(mesh);

        return mesh;
    }
}