GodotComponentTest/scenes/TileInstanceManager.cs

using System.Diagnostics;
using System.Linq;
using Godot;
using Godot.Collections;

public class TileInstanceManager : Spatial
{
    private readonly Array<SceneTileChunk> _sceneTileChunks = new();
    private MultiMeshInstance _tileMultiMeshInstance;
    private ImageTexture _viewTileTypeTexture;

    private World _world;

    // other members
    [Export] public bool ShowHexTiles;
    [Export] public Vector2 ViewCenterPlaneCoord;

    // ui elements

    // scene nodes

    // resources

    // exports
    [Export] public NodePath World;

    // Called when the node enters the scene tree for the first time.
    public override void _Ready()
    {
        _world = GetNode<World>(World);

        _world.Connect("OnTilesChanged", this, nameof(HandleWorldTileChange));

        _tileMultiMeshInstance = (MultiMeshInstance)FindNode("TileMultiMeshInstance");
        Debug.Assert(_tileMultiMeshInstance != null);
    }


    public override void _Process(float delta)
    {
    }

    private SceneTileChunk CreateSceneTileChunk(Vector2 chunkIndex)
    {
        var sceneTileChunk = new SceneTileChunk(chunkIndex, _tileMultiMeshInstance);

        foreach (var hexTile3D in sceneTileChunk.TileNodes)
        {
            hexTile3D.Connect("TileClicked", this, nameof(OnTileClicked));
            hexTile3D.Connect("TileHovered", this, nameof(OnTileHovered));
        }

        return sceneTileChunk;
    }

    private SceneTileChunk FindSceneTileChunkAtIndex(Vector2 chunkIndex)
    {
        foreach (Spatial child in GetChildren())
        {
            var sceneTileChunk = child as SceneTileChunk;
            if (sceneTileChunk == null) continue;

            if (sceneTileChunk.ChunkIndex == chunkIndex) return sceneTileChunk;
        }

        return null;
    }


    private void HandleWorldTileChange(Array<Vector2> removedChunkIndices, Array<Vector2> addedChunkIndices)
    {
        Array<SceneTileChunk> removedChunks = new();
        foreach (var chunkIndex in removedChunkIndices)
        {
            var chunk = FindSceneTileChunkAtIndex(chunkIndex);
            if (chunk != null) removedChunks.Add(chunk);
        }

        foreach (var chunkIndex in addedChunkIndices)
        {
            SceneTileChunk sceneTileChunk = null;
            if (removedChunks.Count > 0)
            {
                sceneTileChunk = removedChunks[^1];
                removedChunks.RemoveAt(removedChunks.Count - 1);
                GD.Print("Reused SceneTileChunk");
            }
            else
            {
                sceneTileChunk = CreateSceneTileChunk(chunkIndex);
                AddChild(sceneTileChunk);
                GD.Print("Created SceneTileChunk");
            }

            sceneTileChunk.ChunkIndex = chunkIndex;

//            if (ShowHexTiles)
//                foreach (var tile3D in sceneTileChunk.TileNodes)
//                    tile3D.Transform = new Transform(Basis.Identity.Scaled(Vector3.One * 0.95f),
//                        tile3D.Transform.origin);

            _sceneTileChunks.Add(sceneTileChunk);
        }

        GD.Print("Removed Chunks " + removedChunkIndices.Count);
        GD.Print("Added Chunks   " + addedChunkIndices.Count);
        GD.Print("Removed chunk count: " + removedChunks.Count);
    }

    public void OnTileClicked(HexTile3D tile)
    {
        EmitSignal("TileClicked", tile);
    }

    public void OnTileHovered(HexTile3D tile)
    {
        EmitSignal("TileHovered", tile);
    }

    // signals
    [Signal]
    private delegate void TileClicked(HexTile3D tile3d);

    [Signal]
    private delegate void TileHovered(HexTile3D tile3d);

    private class SceneTileChunk : Spatial
    {
        private readonly PackedScene _hexTile3DScene = GD.Load<PackedScene>("res://scenes/HexTile3D.tscn");
        private readonly MultiMeshInstance _multiMeshInstance;
        private readonly HexGrid HexGrid = new();
        private readonly Array<int> TileInstanceIndices = new();

        public readonly Array<HexTile3D> TileNodes = new();
        private Vector2 _chunkIndex = Vector2.Inf;

        public SceneTileChunk(Vector2 chunkIndex, MultiMeshInstance multiMeshInstance)
        {
            var chunkSize = global::World.ChunkSize;

            foreach (var i in Enumerable.Range(0, chunkSize))
            foreach (var j in Enumerable.Range(0, chunkSize))
            {
                var tile3D = (HexTile3D)_hexTile3DScene.Instance();

                var tileTransform = Transform.Identity;
                var centerPlaneCoord = HexGrid.GetHexCenterFromOffset(new Vector2(i, j));
                tileTransform.origin = new Vector3(centerPlaneCoord.x, 0, centerPlaneCoord.y);
                tile3D.Transform = tileTransform;

                TileNodes.Add(tile3D);
                AddChild(tile3D);
            }

            _multiMeshInstance = multiMeshInstance;

            var chunkTileCount = global::World.ChunkSize * global::World.ChunkSize;

            foreach (var i in Enumerable.Range(0, chunkTileCount))
                TileInstanceIndices.Add(_multiMeshInstance.Multimesh.InstanceCount + i);

            _multiMeshInstance.Multimesh.InstanceCount += chunkTileCount;
            _multiMeshInstance.Multimesh.VisibleInstanceCount = _multiMeshInstance.Multimesh.InstanceCount;

            GD.Print("VisibleInstanceCount = " + _multiMeshInstance.Multimesh.VisibleInstanceCount);
            
            ChunkIndex = chunkIndex;
        }

        public Vector2 ChunkIndex
        {
            get => _chunkIndex;

            set
            {
                var chunkTransform = Transform.Identity;
                var chunkOriginPlaneCoord = HexGrid.GetHexCenterFromOffset(value * global::World.ChunkSize);
                chunkTransform.origin = new Vector3(chunkOriginPlaneCoord.x, 0, chunkOriginPlaneCoord.y);
                Transform = chunkTransform;
                _chunkIndex = value;

                var tileOrientation = new Basis(Vector3.Up, 90f * Mathf.Pi / 180f);

                GD.Print("Updating transforms for instances of chunk " + value);
                
                foreach (var i in Enumerable.Range(0, TileInstanceIndices.Count))
                {
                    var column = i % global::World.ChunkSize;
                    var row = i / global::World.ChunkSize;

                    var tilePlaneCoord =
                        HexGrid.GetHexCenterFromOffset(new Vector2(column, row));
                    _multiMeshInstance.Multimesh.SetInstanceTransform(TileInstanceIndices[i],
                        new Transform(tileOrientation,
                            chunkTransform.origin + new Vector3(tilePlaneCoord.x, 0, tilePlaneCoord.y)));
                }
            }
        }
    }
}