EXPERIMENTAL: Metal backend (#441)

This is not a continuation of the Metal backend; this is simply bringing
the branch up to date and merging it as-is behind an experiment.

---------

Co-authored-by: Isaac Marovitz <isaacryu@icloud.com>
Co-authored-by: Samuliak <samuliak77@gmail.com>
Co-authored-by: SamoZ256 <96914946+SamoZ256@users.noreply.github.com>
Co-authored-by: Isaac Marovitz <42140194+IsaacMarovitz@users.noreply.github.com>
Co-authored-by: riperiperi <rhy3756547@hotmail.com>
Co-authored-by: Gabriel A <gab.dark.100@gmail.com>

src/Ryujinx.Graphics.Metal/BackgroundResources.cs

@@ -0,0 +1,107 @@
+using SharpMetal.Metal;
+using System;
+using System.Collections.Generic;
+using System.Runtime.Versioning;
+using System.Threading;
+
+namespace Ryujinx.Graphics.Metal
+{
+    [SupportedOSPlatform("macos")]
+    class BackgroundResource : IDisposable
+    {
+        private readonly MetalRenderer _renderer;
+
+        private CommandBufferPool _pool;
+        private PersistentFlushBuffer _flushBuffer;
+
+        public BackgroundResource(MetalRenderer renderer)
+        {
+            _renderer = renderer;
+        }
+
+        public CommandBufferPool GetPool()
+        {
+            if (_pool == null)
+            {
+                MTLCommandQueue queue = _renderer.BackgroundQueue;
+                _pool = new CommandBufferPool(queue, true);
+                _pool.Initialize(null); // TODO: Proper encoder factory for background render/compute
+            }
+
+            return _pool;
+        }
+
+        public PersistentFlushBuffer GetFlushBuffer()
+        {
+            _flushBuffer ??= new PersistentFlushBuffer(_renderer);
+
+            return _flushBuffer;
+        }
+
+        public void Dispose()
+        {
+            _pool?.Dispose();
+            _flushBuffer?.Dispose();
+        }
+    }
+
+    [SupportedOSPlatform("macos")]
+    class BackgroundResources : IDisposable
+    {
+        private readonly MetalRenderer _renderer;
+
+        private readonly Dictionary<Thread, BackgroundResource> _resources;
+
+        public BackgroundResources(MetalRenderer renderer)
+        {
+            _renderer = renderer;
+
+            _resources = new Dictionary<Thread, BackgroundResource>();
+        }
+
+        private void Cleanup()
+        {
+            lock (_resources)
+            {
+                foreach (KeyValuePair<Thread, BackgroundResource> tuple in _resources)
+                {
+                    if (!tuple.Key.IsAlive)
+                    {
+                        tuple.Value.Dispose();
+                        _resources.Remove(tuple.Key);
+                    }
+                }
+            }
+        }
+
+        public BackgroundResource Get()
+        {
+            Thread thread = Thread.CurrentThread;
+
+            lock (_resources)
+            {
+                if (!_resources.TryGetValue(thread, out BackgroundResource resource))
+                {
+                    Cleanup();
+
+                    resource = new BackgroundResource(_renderer);
+
+                    _resources[thread] = resource;
+                }
+
+                return resource;
+            }
+        }
+
+        public void Dispose()
+        {
+            lock (_resources)
+            {
+                foreach (var resource in _resources.Values)
+                {
+                    resource.Dispose();
+                }
+            }
+        }
+    }
+}