VideoCommon: Abstract bounding box

This moves much of the duplicated bounding box code into VideoCommon,
leaving only the specific buffer implementations in each backend.

Source/Core/VideoCommon/BoundingBox.h

@@ -3,40 +3,48 @@
 
 #pragma once
 
+#include <array>
+#include <vector>
+
 #include "Common/CommonTypes.h"
 
 class PointerWrap;
 
-// Bounding Box manager
-namespace BoundingBox
+using BBoxType = s32;
+constexpr u32 NUM_BBOX_VALUES = 4;
+
+class BoundingBox
 {
-// Indicates a coordinate of the bounding box.
-enum class Coordinate
-{
-  Left,    // The X coordinate of the left side of the bounding box.
-  Right,   // The X coordinate of the right side of the bounding box.
-  Top,     // The Y coordinate of the top of the bounding box.
-  Bottom,  // The Y coordinate of the bottom of the bounding box.
+public:
+  explicit BoundingBox() = default;
+  virtual ~BoundingBox() = default;
+
+  bool IsEnabled() const { return m_is_active; }
+  void Enable();
+  void Disable();
+
+  void Flush();
+
+  u16 Get(u32 index);
+  void Set(u32 index, u16 value);
+
+  void DoState(PointerWrap& p);
+
+  // Initialize, Read, and Write are only safe to call if the backend supports bounding box,
+  // otherwise unexpected exceptions can occur
+  virtual bool Initialize() = 0;
+
+protected:
+  virtual std::vector<BBoxType> Read(u32 index, u32 length) = 0;
+  // TODO: This can likely use std::span once we're on C++20
+  virtual void Write(u32 index, const std::vector<BBoxType>& values) = 0;
+
+private:
+  void Readback();
+
+  bool m_is_active = false;
+
+  std::array<BBoxType, NUM_BBOX_VALUES> m_values = {};
+  std::array<bool, NUM_BBOX_VALUES> m_dirty = {};
+  bool m_is_valid = true;
 };
-
-// Enables bounding box.
-void Enable();
-
-// Disables bounding box.
-void Disable();
-
-// Determines if bounding box is enabled.
-bool IsEnabled();
-
-// Gets a particular coordinate for the bounding box.
-u16 GetCoordinate(Coordinate coordinate);
-
-// Sets a particular coordinate for the bounding box.
-void SetCoordinate(Coordinate coordinate, u16 value);
-
-// Updates all bounding box coordinates.
-void Update(u16 left, u16 right, u16 top, u16 bottom);
-
-// Save state
-void DoState(PointerWrap& p);
-}  // namespace BoundingBox