StateWrapper: Track save state version

src/common/state_wrapper.cpp

@@ -5,7 +5,10 @@
 #include <cstring>
 Log_SetChannel(StateWrapper);
 
-StateWrapper::StateWrapper(ByteStream* stream, Mode mode) : m_stream(stream), m_mode(mode) {}
+StateWrapper::StateWrapper(ByteStream* stream, Mode mode, u32 version)
+  : m_stream(stream), m_mode(mode), m_version(version)
+{
+}
 
 StateWrapper::~StateWrapper() = default;
 

src/common/state_wrapper.h

@@ -20,7 +20,7 @@ public:
     Write
   };
 
-  StateWrapper(ByteStream* stream, Mode mode);
+  StateWrapper(ByteStream* stream, Mode mode, u32 version);
   StateWrapper(const StateWrapper&) = delete;
   ~StateWrapper();
 
@@ -30,6 +30,7 @@ public:
   bool IsWriting() const { return (m_mode == Mode::Write); }
   Mode GetMode() const { return m_mode; }
   void SetMode(Mode mode) { m_mode = mode; }
+  u32 GetVersion() const { return m_version; }
 
   /// Overload for integral or floating-point types. Writes bytes as-is.
   template<typename T, std::enable_if_t<std::is_integral_v<T> || std::is_floating_point_v<T>, int> = 0>
@@ -175,8 +176,21 @@ public:
 
   bool DoMarker(const char* marker);
 
+  template<typename T>
+  void DoEx(T* data, u32 version_introduced, T default_value)
+  {
+    if (m_version < version_introduced)
+    {
+      *data = std::move(default_value);
+      return;
+    }
+
+    Do(data);
+  }
+
 private:
   ByteStream* m_stream;
   Mode m_mode;
+  u32 m_version;
   bool m_error = false;
 };

src/core/save_state_version.h

@@ -3,6 +3,7 @@
 
 static constexpr u32 SAVE_STATE_MAGIC = 0x43435544;
 static constexpr u32 SAVE_STATE_VERSION = 42;
+static constexpr u32 SAVE_STATE_MINIMUM_VERSION = 42;
 
 #pragma pack(push, 4)
 struct SAVE_STATE_HEADER

src/core/system.cpp

@@ -491,7 +491,7 @@ bool RecreateGPU(GPURenderer renderer)
 
   // save current state
   std::unique_ptr<ByteStream> state_stream = ByteStream_CreateGrowableMemoryStream();
-  StateWrapper sw(state_stream.get(), StateWrapper::Mode::Write);
+  StateWrapper sw(state_stream.get(), StateWrapper::Mode::Write, SAVE_STATE_VERSION);
   const bool state_valid = g_gpu->DoState(sw) && TimingEvents::DoState(sw);
   if (!state_valid)
     Log_ErrorPrintf("Failed to save old GPU state when switching renderers");
@@ -946,12 +946,12 @@ bool DoLoadState(ByteStream* state, bool force_software_renderer)
   if (header.magic != SAVE_STATE_MAGIC)
     return false;
 
-  if (header.version != SAVE_STATE_VERSION)
+  if (header.version < SAVE_STATE_MINIMUM_VERSION)
   {
     g_host_interface->ReportFormattedError(
       g_host_interface->TranslateString("System",
-                                        "Save state is incompatible: expecting version %u but state is version %u."),
-      SAVE_STATE_VERSION, header.version);
+                                        "Save state is incompatible: minimum version is %u but state is version %u."),
+      SAVE_STATE_MINIMUM_VERSION, header.version);
     return false;
   }
 
@@ -1041,7 +1041,7 @@ bool DoLoadState(ByteStream* state, bool force_software_renderer)
   if (!state->SeekAbsolute(header.offset_to_data))
     return false;
 
-  StateWrapper sw(state, StateWrapper::Mode::Read);
+  StateWrapper sw(state, StateWrapper::Mode::Read, header.version);
   if (!DoState(sw))
     return false;
 
@@ -1108,7 +1108,7 @@ bool SaveState(ByteStream* state, u32 screenshot_size /* = 128 */)
 
     g_gpu->RestoreGraphicsAPIState();
 
-    StateWrapper sw(state, StateWrapper::Mode::Write);
+    StateWrapper sw(state, StateWrapper::Mode::Write, SAVE_STATE_VERSION);
     const bool result = DoState(sw);
 
     g_gpu->ResetGraphicsAPIState();