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

using System.Globalization;
using OpenTK.Mathematics;

namespace Engine.Asset.Mesh.Loader;

public class StlMeshLoader : IMeshLoader
{
    private static readonly StlMeshLoader 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 currentNormal = new Vector3();
        var index = 0u;

        using var reader = new StreamReader(path);
        while (reader.ReadLine() is { } line)
        {
            line = line.Trim();

            if (string.IsNullOrWhiteSpace(line) || line.StartsWith("solid") || line.StartsWith("outer loop") ||
                line.StartsWith("endloop"))
                continue;
            if (line.StartsWith("endsolid"))
                break;

            var parts = line.Split(' ', StringSplitOptions.RemoveEmptyEntries);

            switch (parts[0])
            {
                case "facet" when parts[1] == "normal" && parameters.HasFlag(MeshLoaderParameters.LoadNormals):
                    currentNormal = new Vector3(
                        float.Parse(parts[2], CultureInfo.InvariantCulture),
                        float.Parse(parts[3], CultureInfo.InvariantCulture),
                        float.Parse(parts[4], CultureInfo.InvariantCulture)
                    );
                    break;
                case "vertex":
                {
                    var vertex = new Vector3(
                        float.Parse(parts[1], CultureInfo.InvariantCulture),
                        float.Parse(parts[2], CultureInfo.InvariantCulture),
                        float.Parse(parts[3], CultureInfo.InvariantCulture)
                    );

                    mesh.VerticesInternal.Add(new Mesh.Vertex
                    {
                        Position = vertex,
                        Normal = currentNormal
                    });
                    mesh.IndicesInternal.Add(index++);
                    break;
                }
            }
        }

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

        return mesh;
    }
}