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/PersistentFlushBuffer.cs

@@ -0,0 +1,99 @@
+using Ryujinx.Graphics.GAL;
+using System;
+using System.Runtime.Versioning;
+
+namespace Ryujinx.Graphics.Metal
+{
+    [SupportedOSPlatform("macos")]
+    internal class PersistentFlushBuffer : IDisposable
+    {
+        private readonly MetalRenderer _renderer;
+
+        private BufferHolder _flushStorage;
+
+        public PersistentFlushBuffer(MetalRenderer renderer)
+        {
+            _renderer = renderer;
+        }
+
+        private BufferHolder ResizeIfNeeded(int size)
+        {
+            var flushStorage = _flushStorage;
+
+            if (flushStorage == null || size > _flushStorage.Size)
+            {
+                flushStorage?.Dispose();
+
+                flushStorage = _renderer.BufferManager.Create(size);
+                _flushStorage = flushStorage;
+            }
+
+            return flushStorage;
+        }
+
+        public Span<byte> GetBufferData(CommandBufferPool cbp, BufferHolder buffer, int offset, int size)
+        {
+            var flushStorage = ResizeIfNeeded(size);
+            Auto<DisposableBuffer> srcBuffer;
+
+            using (var cbs = cbp.Rent())
+            {
+                srcBuffer = buffer.GetBuffer();
+                var dstBuffer = flushStorage.GetBuffer();
+
+                if (srcBuffer.TryIncrementReferenceCount())
+                {
+                    BufferHolder.Copy(cbs, srcBuffer, dstBuffer, offset, 0, size, registerSrcUsage: false);
+                }
+                else
+                {
+                    // Source buffer is no longer alive, don't copy anything to flush storage.
+                    srcBuffer = null;
+                }
+            }
+
+            flushStorage.WaitForFences();
+            srcBuffer?.DecrementReferenceCount();
+            return flushStorage.GetDataStorage(0, size);
+        }
+
+        public Span<byte> GetTextureData(CommandBufferPool cbp, Texture view, int size)
+        {
+            TextureCreateInfo info = view.Info;
+
+            var flushStorage = ResizeIfNeeded(size);
+
+            using (var cbs = cbp.Rent())
+            {
+                var buffer = flushStorage.GetBuffer().Get(cbs).Value;
+                var image = view.GetHandle();
+
+                view.CopyFromOrToBuffer(cbs, buffer, image, size, true, 0, 0, info.GetLayers(), info.Levels, singleSlice: false);
+            }
+
+            flushStorage.WaitForFences();
+            return flushStorage.GetDataStorage(0, size);
+        }
+
+        public Span<byte> GetTextureData(CommandBufferPool cbp, Texture view, int size, int layer, int level)
+        {
+            var flushStorage = ResizeIfNeeded(size);
+
+            using (var cbs = cbp.Rent())
+            {
+                var buffer = flushStorage.GetBuffer().Get(cbs).Value;
+                var image = view.GetHandle();
+
+                view.CopyFromOrToBuffer(cbs, buffer, image, size, true, layer, level, 1, 1, singleSlice: true);
+            }
+
+            flushStorage.WaitForFences();
+            return flushStorage.GetDataStorage(0, size);
+        }
+
+        public void Dispose()
+        {
+            _flushStorage.Dispose();
+        }
+    }
+}