Add basic support for rewinding (not enabled.)

Core/SaveState.cpp

@@ -32,6 +32,7 @@
 #include "Core/MemMap.h"
 #include "Core/MIPS/MIPS.h"
 #include "Core/MIPS/JitCommon/JitCommon.h"
+#include "GPU/GPUState.h"
 #include "UI/OnScreenDisplay.h"
 #include "i18n/i18n.h"
 
@@ -47,6 +48,7 @@ namespace SaveState
 		SAVESTATE_SAVE,
 		SAVESTATE_LOAD,
 		SAVESTATE_VERIFY,
+		SAVESTATE_REWIND,
 	};
 
 	struct Operation
@@ -62,10 +64,58 @@ namespace SaveState
 		void *cbUserData;
 	};
 
+	struct StateRingbuffer
+	{
+		StateRingbuffer(int size) : first_(0), next_(0), size_(size)
+		{
+			states_.resize(size);
+		}
+
+		CChunkFileReader::Error Save()
+		{
+			int n = next_++ % size_;
+			if (n == first_)
+				++first_;
+
+			SaveStart state;
+			size_t sz = CChunkFileReader::MeasurePtr(state);
+			if (states_[n].size() < sz)
+				states_[n].resize(sz);
+
+			return CChunkFileReader::SavePtr(states_[n].data(), state);
+		}
+
+		CChunkFileReader::Error Restore()
+		{
+			// No valid states left.
+			if (next_ == first_)
+				return CChunkFileReader::ERROR_BAD_FILE;
+
+			int n = (next_-- + size_) % size_;
+			if (states_[n].empty())
+				return CChunkFileReader::ERROR_BAD_FILE;
+			
+			SaveStart state;
+			return CChunkFileReader::LoadPtr(states_[n].data(), state);
+		}
+
+		typedef std::vector<u8> StateBuffer;
+		int first_;
+		int next_;
+		int size_;
+		std::vector<StateBuffer> states_;
+	};
+
 	static bool needsProcess = false;
 	static std::vector<Operation> pending;
 	static std::recursive_mutex mutex;
 
+	// TODO: Should this be configurable?
+	static const int REWIND_NUM_STATES = 5;
+	static StateRingbuffer rewindStates(REWIND_NUM_STATES);
+	// TODO: g_Config setting or something instead.
+	static int rewindStateFreq = 0;
+
 	void SaveStart::DoState(PointerWrap &p)
 	{
 		auto s = p.Section("SaveStart", 1);
@@ -120,6 +170,11 @@ namespace SaveState
 		Enqueue(Operation(SAVESTATE_VERIFY, std::string(""), callback, cbUserData));
 	}
 
+	void Rewind(Callback callback, void *cbUserData)
+	{
+		Enqueue(Operation(SAVESTATE_REWIND, std::string(""), callback, cbUserData));
+	}
+
 
 	// Slot utilities
 
@@ -230,6 +285,12 @@ namespace SaveState
 
 	void Process()
 	{
+		if (rewindStateFreq != 0)
+		{
+			if (gpuStats.numFlips % rewindStateFreq == 0)
+				rewindStates.Save();
+		}
+
 		if (!needsProcess)
 			return;
 		needsProcess = false;
@@ -289,6 +350,32 @@ namespace SaveState
 				callbackResult = CChunkFileReader::Verify(state) == CChunkFileReader::ERROR_NONE;
 				break;
 
+			case SAVESTATE_REWIND:
+				INFO_LOG(COMMON, "Rewinding to recent savestate snapshot");
+				result = rewindStates.Restore();
+				if (result == CChunkFileReader::ERROR_NONE) {
+					osm.Show(s->T("Loaded State"), 2.0);
+					callbackResult = true;
+				} else if (result == CChunkFileReader::ERROR_BROKEN_STATE) {
+					// Cripes.  Good news is, we might have more.  Let's try those too, better than a reset.
+					do
+						result = rewindStates.Restore();
+					while (result == CChunkFileReader::ERROR_BROKEN_STATE);
+
+					if (result == CChunkFileReader::ERROR_NONE) {
+						osm.Show(s->T("Loaded State"), 2.0);
+						callbackResult = true;
+					} else {
+						// We tried our best.
+						HandleFailure();
+						callbackResult = false;
+					}
+				} else {
+					osm.Show(s->T("Load savestate failed"), 2.0);
+					callbackResult = false;
+				}
+				break;
+
 			default:
 				ERROR_LOG(COMMON, "Savestate failure: unknown operation type %d", op.type);
 				callbackResult = false;