VideoBackends: Add Metal renderer

Source/Core/VideoBackends/Metal/MRCHelpers.h

@@ -0,0 +1,81 @@
+// Copyright 2022 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+// clang-format off
+#ifndef __OBJC__
+  #error This header is for use with Objective-C++ only.
+#endif
+#if __has_feature(objc_arc)
+  #error This file is for manual reference counting!  Compile without -fobjc-arc
+#endif
+// clang-format on
+
+#pragma once
+
+#include <cstddef>
+#include <utility>
+
+/// Managed Obj-C pointer
+template <typename T>
+class MRCOwned
+{
+  T ptr;
+  MRCOwned(T ptr) : ptr(ptr) {}
+
+public:
+  MRCOwned() : ptr(nullptr) {}
+  MRCOwned(std::nullptr_t) : ptr(nullptr) {}
+  MRCOwned(MRCOwned&& other) : ptr(other.ptr) { other.ptr = nullptr; }
+  MRCOwned(const MRCOwned& other) : ptr(other.ptr) { [ptr retain]; }
+  ~MRCOwned()
+  {
+    if (ptr)
+      [ptr release];
+  }
+  operator T() const { return ptr; }
+  MRCOwned& operator=(const MRCOwned& other)
+  {
+    [other.ptr retain];
+    if (ptr)
+      [ptr release];
+    ptr = other.ptr;
+    return *this;
+  }
+  MRCOwned& operator=(MRCOwned&& other)
+  {
+    std::swap(ptr, other.ptr);
+    return *this;
+  }
+  void Reset()
+  {
+    [ptr release];
+    ptr = nullptr;
+  }
+  T Disown()
+  {
+    T tmp = ptr;
+    ptr = nullptr;
+    return tmp;
+  }
+  T Get() const { return ptr; }
+  static MRCOwned Transfer(T ptr) { return MRCOwned(ptr); }
+  static MRCOwned Retain(T ptr)
+  {
+    [ptr retain];
+    return MRCOwned(ptr);
+  }
+};
+
+/// Take ownership of an Obj-C pointer (equivalent to __bridge_transfer)
+template <typename T>
+static inline MRCOwned<T> MRCTransfer(T ptr)
+{
+  return MRCOwned<T>::Transfer(ptr);
+}
+
+/// Retain an Obj-C pointer (equivalent to __bridge)
+template <typename T>
+static inline MRCOwned<T> MRCRetain(T ptr)
+{
+  return MRCOwned<T>::Retain(ptr);
+}