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/IndexBufferPattern.cs

@@ -0,0 +1,118 @@
+using Ryujinx.Graphics.GAL;
+using System;
+using System.Runtime.InteropServices;
+using System.Runtime.Versioning;
+
+namespace Ryujinx.Graphics.Metal
+{
+    [SupportedOSPlatform("macos")]
+    internal class IndexBufferPattern : IDisposable
+    {
+        public int PrimitiveVertices { get; }
+        public int PrimitiveVerticesOut { get; }
+        public int BaseIndex { get; }
+        public int[] OffsetIndex { get; }
+        public int IndexStride { get; }
+        public bool RepeatStart { get; }
+
+        private readonly MetalRenderer _renderer;
+        private int _currentSize;
+        private BufferHandle _repeatingBuffer;
+
+        public IndexBufferPattern(MetalRenderer renderer,
+            int primitiveVertices,
+            int primitiveVerticesOut,
+            int baseIndex,
+            int[] offsetIndex,
+            int indexStride,
+            bool repeatStart)
+        {
+            PrimitiveVertices = primitiveVertices;
+            PrimitiveVerticesOut = primitiveVerticesOut;
+            BaseIndex = baseIndex;
+            OffsetIndex = offsetIndex;
+            IndexStride = indexStride;
+            RepeatStart = repeatStart;
+
+            _renderer = renderer;
+        }
+
+        public int GetPrimitiveCount(int vertexCount)
+        {
+            return Math.Max(0, (vertexCount - BaseIndex) / IndexStride);
+        }
+
+        public int GetConvertedCount(int indexCount)
+        {
+            int primitiveCount = GetPrimitiveCount(indexCount);
+            return primitiveCount * OffsetIndex.Length;
+        }
+
+        public BufferHandle GetRepeatingBuffer(int vertexCount, out int indexCount)
+        {
+            int primitiveCount = GetPrimitiveCount(vertexCount);
+            indexCount = primitiveCount * PrimitiveVerticesOut;
+
+            int expectedSize = primitiveCount * OffsetIndex.Length;
+
+            if (expectedSize <= _currentSize && _repeatingBuffer != BufferHandle.Null)
+            {
+                return _repeatingBuffer;
+            }
+
+            // Expand the repeating pattern to the number of requested primitives.
+            BufferHandle newBuffer = _renderer.BufferManager.CreateWithHandle(expectedSize * sizeof(int));
+
+            // Copy the old data to the new one.
+            if (_repeatingBuffer != BufferHandle.Null)
+            {
+                _renderer.Pipeline.CopyBuffer(_repeatingBuffer, newBuffer, 0, 0, _currentSize * sizeof(int));
+                _renderer.BufferManager.Delete(_repeatingBuffer);
+            }
+
+            _repeatingBuffer = newBuffer;
+
+            // Add the additional repeats on top.
+            int newPrimitives = primitiveCount;
+            int oldPrimitives = (_currentSize) / OffsetIndex.Length;
+
+            int[] newData;
+
+            newPrimitives -= oldPrimitives;
+            newData = new int[expectedSize - _currentSize];
+
+            int outOffset = 0;
+            int index = oldPrimitives * IndexStride + BaseIndex;
+
+            for (int i = 0; i < newPrimitives; i++)
+            {
+                if (RepeatStart)
+                {
+                    // Used for triangle fan
+                    newData[outOffset++] = 0;
+                }
+
+                for (int j = RepeatStart ? 1 : 0; j < OffsetIndex.Length; j++)
+                {
+                    newData[outOffset++] = index + OffsetIndex[j];
+                }
+
+                index += IndexStride;
+            }
+
+            _renderer.SetBufferData(newBuffer, _currentSize * sizeof(int), MemoryMarshal.Cast<int, byte>(newData));
+            _currentSize = expectedSize;
+
+            return newBuffer;
+        }
+
+        public void Dispose()
+        {
+            if (_repeatingBuffer != BufferHandle.Null)
+            {
+                _renderer.BufferManager.Delete(_repeatingBuffer);
+                _repeatingBuffer = BufferHandle.Null;
+            }
+        }
+    }
+}