VideoCommon: add custom asset implementation and asset library that can load an asset

Source/Core/VideoCommon/Assets/CustomAssetLibrary.h

@@ -0,0 +1,49 @@
+// Copyright 2023 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <chrono>
+#include <filesystem>
+#include <map>
+#include <string>
+
+namespace VideoCommon
+{
+class CustomTextureData;
+
+// This class provides functionality to load
+// specific data (like textures).  Where this data
+// is loaded from is implementation defined
+class CustomAssetLibrary
+{
+public:
+  // TODO: this should be std::chrono::system_clock::time_point to
+  // support any type of loader where the time isn't from the filesystem
+  // but there's no way to convert filesystem times to system times
+  // without 'clock_cast', once our builders catch up
+  // to support 'clock_cast' we should update this
+  // For now, it's fine as a filesystem library is all that is
+  // available
+  using TimeType = std::filesystem::file_time_type;
+
+  // The AssetID is a unique identifier for a particular asset
+  using AssetID = std::string;
+
+  struct LoadInfo
+  {
+    std::size_t m_bytes_loaded;
+    CustomAssetLibrary::TimeType m_load_time;
+  };
+
+  // Loads a texture, if there are no levels, bytes loaded will be empty
+  virtual LoadInfo LoadTexture(const AssetID& asset_id, CustomTextureData* data) = 0;
+
+  // Gets the last write time for a given asset id
+  virtual TimeType GetLastAssetWriteTime(const AssetID& asset_id) const = 0;
+
+  // Loads a texture as a game texture, providing additional checks like confirming
+  // each mip level size is correct and that the format is consistent across the data
+  LoadInfo LoadGameTexture(const AssetID& asset_id, CustomTextureData* data);
+};
+}  // namespace VideoCommon