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/VertexBufferState.cs

@@ -0,0 +1,60 @@
+using Ryujinx.Graphics.GAL;
+using SharpMetal.Metal;
+using System;
+using System.Runtime.Versioning;
+
+namespace Ryujinx.Graphics.Metal
+{
+    [SupportedOSPlatform("macos")]
+    readonly internal struct VertexBufferState
+    {
+        public static VertexBufferState Null => new(BufferHandle.Null, 0, 0, 0);
+
+        private readonly BufferHandle _handle;
+        private readonly int _offset;
+        private readonly int _size;
+
+        public readonly int Stride;
+        public readonly int Divisor;
+
+        public VertexBufferState(BufferHandle handle, int offset, int size, int divisor, int stride = 0)
+        {
+            _handle = handle;
+            _offset = offset;
+            _size = size;
+
+            Stride = stride;
+            Divisor = divisor;
+        }
+
+        public (MTLBuffer, int) GetVertexBuffer(BufferManager bufferManager, CommandBufferScoped cbs)
+        {
+            Auto<DisposableBuffer> autoBuffer = null;
+
+            if (_handle != BufferHandle.Null)
+            {
+                // TODO: Handle restride if necessary
+
+                autoBuffer = bufferManager.GetBuffer(_handle, false, out int size);
+
+                // The original stride must be reapplied in case it was rewritten.
+                // TODO: Handle restride if necessary
+
+                if (_offset >= size)
+                {
+                    autoBuffer = null;
+                }
+            }
+
+            if (autoBuffer != null)
+            {
+                int offset = _offset;
+                var buffer = autoBuffer.Get(cbs, offset, _size).Value;
+
+                return (buffer, offset);
+            }
+
+            return (new MTLBuffer(IntPtr.Zero), 0);
+        }
+    }
+}