Implement D3D12 backend

Source/Core/VideoBackends/D3D12/StreamBuffer.h

@@ -0,0 +1,56 @@
+// Copyright 2019 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <deque>
+#include <utility>
+
+#include "Common/CommonTypes.h"
+#include "VideoBackends/D3D12/Common.h"
+
+namespace DX12
+{
+class StreamBuffer
+{
+public:
+  StreamBuffer();
+  ~StreamBuffer();
+
+  bool AllocateBuffer(u32 size);
+
+  ID3D12Resource* GetBuffer() const { return m_buffer; }
+  D3D12_GPU_VIRTUAL_ADDRESS GetGPUPointer() const { return m_gpu_pointer; }
+  u8* GetHostPointer() const { return m_host_pointer; }
+  u8* GetCurrentHostPointer() const { return m_host_pointer + m_current_offset; }
+  D3D12_GPU_VIRTUAL_ADDRESS GetCurrentGPUPointer() const
+  {
+    return m_gpu_pointer + m_current_offset;
+  }
+  u32 GetSize() const { return m_size; }
+  u32 GetCurrentOffset() const { return m_current_offset; }
+  bool ReserveMemory(u32 num_bytes, u32 alignment);
+  void CommitMemory(u32 final_num_bytes);
+
+private:
+  void UpdateCurrentFencePosition();
+  void UpdateGPUPosition();
+
+  // Waits for as many fences as needed to allocate num_bytes bytes from the buffer.
+  bool WaitForClearSpace(u32 num_bytes);
+
+  u32 m_size = 0;
+  u32 m_current_offset = 0;
+  u32 m_current_gpu_position = 0;
+  u32 m_last_allocation_size = 0;
+
+  ID3D12Resource* m_buffer = nullptr;
+  D3D12_GPU_VIRTUAL_ADDRESS m_gpu_pointer = {};
+  u8* m_host_pointer = nullptr;
+
+  // List of fences and the corresponding positions in the buffer
+  std::deque<std::pair<u64, u32>> m_tracked_fences;
+};
+
+}  // namespace DX12