From 2bf736e3513b82d4b7ddb46b7907460b08d70f6e Mon Sep 17 00:00:00 2001
From: Wojtek Figat <wojtek@figat.pl>
Date: Thu, 22 Jul 2021 11:19:10 +0200
Subject: [PATCH] Add `MeshDataCache` utility for async mesh data caching

---
 Source/Engine/Utilities/MeshDataCache.cs | 138 +++++++++++++++++++++++
 1 file changed, 138 insertions(+)
 create mode 100644 Source/Engine/Utilities/MeshDataCache.cs

diff --git a/Source/Engine/Utilities/MeshDataCache.cs b/Source/Engine/Utilities/MeshDataCache.cs
new file mode 100644
index 000000000..0978bdc40
--- /dev/null
+++ b/Source/Engine/Utilities/MeshDataCache.cs
@@ -0,0 +1,138 @@
+// Copyright (c) 2012-2021 Wojciech Figat. All rights reserved.
+
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace FlaxEngine.Utilities
+{
+    /// <summary>
+    /// Helper utility for caching model meshes data.
+    /// </summary>
+    [HideInEditor]
+    public class MeshDataCache
+    {
+        /// <summary>
+        /// The single mesh data container.
+        /// </summary>
+        public struct MeshData
+        {
+            /// <summary>
+            /// The index buffer.
+            /// </summary>
+            public int[] IndexBuffer;
+
+            /// <summary>
+            /// The vertex buffer.
+            /// </summary>
+            public Mesh.Vertex[] VertexBuffer;
+        }
+
+        private Model _model;
+        private MeshData[][] _meshDatas;
+        private bool _meshDatasInProgress;
+        private bool _meshDatasCancel;
+
+        /// <summary>
+        /// Gets the mesh datas (null if during downloading).
+        /// </summary>
+        public MeshData[][] MeshDatas => _meshDatasInProgress ? null : _meshDatas;
+
+        /// <summary>
+        /// Requests the mesh data.
+        /// </summary>
+        /// <param name="model">The model to get it's data.</param>
+        /// <returns>True if ahs valid data to access, otherwise false if it's during downloading.</returns>
+        public bool RequestMeshData(Model model)
+        {
+            if (model == null)
+                throw new ArgumentNullException();
+            if (_model != model)
+            {
+                // Mode changes so release previous cache
+                Dispose();
+            }
+            if (_meshDatasInProgress)
+            {
+                // Still downloading
+                return false;
+            }
+            if (_meshDatas != null)
+            {
+                // Has valid data
+                return true;
+            }
+
+            // Start downloading
+            _model = model;
+            _meshDatasInProgress = true;
+            _meshDatasCancel = false;
+            Task.Run(new Action(DownloadMeshData));
+            return false;
+        }
+
+        /// <summary>
+        /// Releases cache.
+        /// </summary>
+        public void Dispose()
+        {
+            WaitForMeshDataRequestEnd();
+            _meshDatas = null;
+            _meshDatasInProgress = false;
+        }
+
+        /// <summary>
+        /// Waits for mesh data request to end. Does nothing if already has valid data or no valid request pending.
+        /// </summary>
+        public void WaitForMeshDataRequestEnd()
+        {
+            if (_meshDatasInProgress)
+            {
+                _meshDatasCancel = true;
+                for (int i = 0; i < 500 && _meshDatasInProgress; i++)
+                    Thread.Sleep(10);
+            }
+        }
+
+        private void DownloadMeshData()
+        {
+            try
+            {
+                if (!_model)
+                {
+                    _meshDatasInProgress = false;
+                    return;
+                }
+                var lods = _model.LODs;
+                _meshDatas = new MeshData[lods.Length][];
+
+                for (int lodIndex = 0; lodIndex < lods.Length && !_meshDatasCancel; lodIndex++)
+                {
+                    var lod = lods[lodIndex];
+                    var meshes = lod.Meshes;
+                    _meshDatas[lodIndex] = new MeshData[meshes.Length];
+
+                    for (int meshIndex = 0; meshIndex < meshes.Length && !_meshDatasCancel; meshIndex++)
+                    {
+                        var mesh = meshes[meshIndex];
+                        _meshDatas[lodIndex][meshIndex] = new MeshData
+                        {
+                            IndexBuffer = mesh.DownloadIndexBuffer(),
+                            VertexBuffer = mesh.DownloadVertexBuffer()
+                        };
+                    }
+                }
+            }
+            catch (Exception ex)
+            {
+                Debug.Logger.LogHandler.LogWrite(LogType.Warning, "Failed to get mesh data.");
+                Debug.Logger.LogHandler.LogWrite(LogType.Warning, _model?.ToString() ?? string.Empty);
+                Debug.Logger.LogHandler.LogException(ex, null);
+            }
+            finally
+            {
+                _meshDatasInProgress = false;
+            }
+        }
+    }
+}