thief-mission-viewer/project/code/TMV/Model.cs

using System.Collections.Generic;
using System.IO;
using Godot;
using KeepersCompound.LGS;
using KeepersCompound.TMV.UI;

namespace KeepersCompound.TMV;

public partial class Model : Node3D
{
    public override void _Ready()
    {
        var modelSelector = GetNode<Control>("%ModelSelector") as ModelSelector;
        modelSelector.LoadModel += BuildModel;
    }

    public void BuildModel(string rootPath, string modelPath)
    {
        foreach (var node in GetChildren())
        {
            node.QueueFree();
        }

        var modelFile = new ModelFile(modelPath);
        if (modelFile == null)
        {
            GD.Print($"Failed to load model file: {modelPath}");
            return;
        }

        // TODO: Remove this disgusting hack. Not only is it a hack, it doesn't support custom models
        var baseDir = ProjectSettings.GlobalizePath($"user://objects/tmp");
        var options = new EnumerationOptions
        {
            MatchCasing = MatchCasing.CaseInsensitive,
            RecurseSubdirectories = true,
        };
        var materials = new List<StandardMaterial3D>();
        foreach (var material in modelFile.Materials)
        {
            if (material.Type == 0)
            {
                var paths = Directory.GetFiles(baseDir, material.Name, options);
                if (paths.IsEmpty()) continue;

                materials.Add(new StandardMaterial3D
                {
                    AlbedoTexture = TextureLoader.LoadTexture(paths[0])
                });
            }
            else
            {
                var b = (material.Handle) & 0xff;
                var g = (material.Handle >> 8) & 0xff;
                var r = (material.Handle >> 16) & 0xff;
                var colour = new Color(r / 255.0f, g / 255.0f, b / 255.0f, 1.0f);
                materials.Add(new StandardMaterial3D
                {
                    AlbedoColor = colour
                });
            }
        }

        var surfaceDataMap = new Dictionary<int, MeshSurfaceData>();
        foreach (var poly in modelFile.Polygons)
        {
            var vertices = new List<Vector3>();
            var normal = modelFile.Normals[poly.Normal].ToGodotVec3();
            var uvs = new List<Vector2>();
            for (var i = 0; i < poly.VertexCount; i++)
            {
                var vertex = modelFile.Vertices[poly.VertexIndices[i]];
                vertices.Add(vertex.ToGodotVec3());
                if (i < poly.UvIndices.Length)
                {
                    var uv = modelFile.Uvs[poly.UvIndices[i]];
                    uvs.Add(new Vector2(uv.X, uv.Y));
                }
                else
                {
                    uvs.Add(Vector2.Zero);
                }
            }

            if (!surfaceDataMap.ContainsKey(poly.Data))
            {
                surfaceDataMap.Add(poly.Data, new MeshSurfaceData());
            }

            surfaceDataMap[poly.Data].AddPolygon(vertices, normal, uvs, uvs);
        }

        var mesh = new ArrayMesh();
        foreach (var (materialId, surfaceData) in surfaceDataMap)
        {
            var array = surfaceData.BuildSurfaceArray();
            var surfaceIdx = mesh.GetSurfaceCount();
            mesh.AddSurfaceFromArrays(Mesh.PrimitiveType.Triangles, array);
            for (var i = 0; i < materials.Count; i++)
            {
                var m = modelFile.Materials[i];
                if (m.Slot == materialId)
                {
                    mesh.SurfaceSetMaterial(surfaceIdx, materials[i]);
                    break;
                }
            }
        }

        var pos = -modelFile.Header.Center.ToGodotVec3();
        var meshInstance = new MeshInstance3D { Mesh = mesh, Position = pos };
        AddChild(meshInstance);
    }
}