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/IndexBufferState.cs

@@ -0,0 +1,103 @@
+using Ryujinx.Graphics.GAL;
+using SharpMetal.Metal;
+using System;
+using System.Runtime.Versioning;
+
+namespace Ryujinx.Graphics.Metal
+{
+    [SupportedOSPlatform("macos")]
+    readonly internal struct IndexBufferState
+    {
+        public static IndexBufferState Null => new(BufferHandle.Null, 0, 0);
+
+        private readonly int _offset;
+        private readonly int _size;
+        private readonly IndexType _type;
+
+        private readonly BufferHandle _handle;
+
+        public IndexBufferState(BufferHandle handle, int offset, int size, IndexType type = IndexType.UInt)
+        {
+            _handle = handle;
+            _offset = offset;
+            _size = size;
+            _type = type;
+        }
+
+        public (MTLBuffer, int, MTLIndexType) GetIndexBuffer(MetalRenderer renderer, CommandBufferScoped cbs)
+        {
+            Auto<DisposableBuffer> autoBuffer;
+            int offset, size;
+            MTLIndexType type;
+
+            if (_type == IndexType.UByte)
+            {
+                // Index type is not supported. Convert to I16.
+                autoBuffer = renderer.BufferManager.GetBufferI8ToI16(cbs, _handle, _offset, _size);
+
+                type = MTLIndexType.UInt16;
+                offset = 0;
+                size = _size * 2;
+            }
+            else
+            {
+                autoBuffer = renderer.BufferManager.GetBuffer(_handle, false, out int bufferSize);
+
+                if (_offset >= bufferSize)
+                {
+                    autoBuffer = null;
+                }
+
+                type = _type.Convert();
+                offset = _offset;
+                size = _size;
+            }
+
+            if (autoBuffer != null)
+            {
+                DisposableBuffer buffer = autoBuffer.Get(cbs, offset, size);
+
+                return (buffer.Value, offset, type);
+            }
+
+            return (new MTLBuffer(IntPtr.Zero), 0, MTLIndexType.UInt16);
+        }
+
+        public (MTLBuffer, int, MTLIndexType) GetConvertedIndexBuffer(
+            MetalRenderer renderer,
+            CommandBufferScoped cbs,
+            int firstIndex,
+            int indexCount,
+            int convertedCount,
+            IndexBufferPattern pattern)
+        {
+            // Convert the index buffer using the given pattern.
+            int indexSize = GetIndexSize();
+
+            int firstIndexOffset = firstIndex * indexSize;
+
+            var autoBuffer = renderer.BufferManager.GetBufferTopologyConversion(cbs, _handle, _offset + firstIndexOffset, indexCount * indexSize, pattern, indexSize);
+
+            int size = convertedCount * 4;
+
+            if (autoBuffer != null)
+            {
+                DisposableBuffer buffer = autoBuffer.Get(cbs, 0, size);
+
+                return (buffer.Value, 0, MTLIndexType.UInt32);
+            }
+
+            return (new MTLBuffer(IntPtr.Zero), 0, MTLIndexType.UInt32);
+        }
+
+        private int GetIndexSize()
+        {
+            return _type switch
+            {
+                IndexType.UInt => 4,
+                IndexType.UShort => 2,
+                _ => 1,
+            };
+        }
+    }
+}