First pass at continuous state saving in emulation mode, accessible by the debugger:

- Toggle this with Alt-r.  When enabled, state is saved each frame to memory (up to 100 slots)
- Upon entering the debugger, rewind is immediately available, allowing to rewind (for example) back past a breakpoint
- Testing is definitely required.

src/common/RewindManager.hxx

@@ -44,7 +44,7 @@ class RewindManager
 
       @param message  Message to display when rewinding to this state
     */
-    bool addState(const string& message = "");
+    bool addState(const string& message);
 
     /**
       Rewind one level of the state list, and display the message associated

src/common/StateManager.cxx

@@ -35,16 +35,16 @@
 StateManager::StateManager(OSystem& osystem)
   : myOSystem(osystem),
     myCurrentSlot(0),
-    myActiveMode(kOffMode)
+    myActiveMode(Mode::Off)
 {
   myRewindManager = make_unique<RewindManager>(myOSystem, *this);
   reset();
 }
 
-// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-bool StateManager::toggleRecordMode()
-{
 #if 0
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+void StateManager::toggleRecordMode()
+{
   if(myActiveMode != kMovieRecordMode)  // Turn on movie record mode
   {
     myActiveMode = kOffMode;
@@ -81,15 +81,8 @@ bool StateManager::toggleRecordMode()
   }
 
   return myActiveMode == kMovieRecordMode;
-#endif
-  return false;
-}
-
-// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-bool StateManager::toggleRewindMode()
-{
-  // FIXME - For now, I'm going to use this to activate movie playback
-#if 0
+////////////////////////////////////////////////////////
+// FIXME - For now, I'm going to use this to activate movie playback
   // Close the writer, since we're about to re-open in read mode
   myMovieWriter.close();
 
@@ -128,34 +121,44 @@ bool StateManager::toggleRewindMode()
     myMovieReader.close();
     return false;
   }
-
-  return myActiveMode == kMoviePlaybackMode;
+}
 #endif
-  return false;
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+void StateManager::toggleRewindMode()
+{
+  myActiveMode = myActiveMode == Mode::Rewind ? Mode::Off : Mode::Rewind;
+  if(myActiveMode == Mode::Rewind)
+    myOSystem.frameBuffer().showMessage("Continuous rewind enabled");
+  else
+    myOSystem.frameBuffer().showMessage("Continuous rewind disabled");
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 void StateManager::update()
 {
-#if 0
   switch(myActiveMode)
   {
-    case kMovieRecordMode:
+    case Mode::Rewind:
+      myRewindManager->addState("1 frame");
+      break;
+
+#if 0
+    case Mode::MovieRecord:
       myOSystem.console().controller(Controller::Left).save(myMovieWriter);
       myOSystem.console().controller(Controller::Right).save(myMovieWriter);
       myOSystem.console().switches().save(myMovieWriter);
       break;
 
-    case kMoviePlaybackMode:
+    case Mode::MoviePlayback:
       myOSystem.console().controller(Controller::Left).load(myMovieReader);
       myOSystem.console().controller(Controller::Right).load(myMovieReader);
       myOSystem.console().switches().load(myMovieReader);
       break;
-
+#endif
     default:
       break;
   }
-#endif
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

src/common/StateManager.hxx

@@ -33,41 +33,58 @@ class OSystem;
 class StateManager
 {
   public:
+    enum class Mode {
+      Off,
+      Rewind,
+      MovieRecord,
+      MoviePlayback
+    };
+
     /**
-      Create a new statemananger class
+      Create a new statemananger class.
     */
     StateManager(OSystem& osystem);
 
   public:
     /**
-      Answers whether the manager is in record or playback mode
+      Answers whether the manager is in record or playback mode.
     */
-    bool isActive() const { return myActiveMode != kOffMode; }
+    Mode mode() const { return myActiveMode; }
 
-    bool toggleRecordMode();
-    bool toggleRewindMode();
+#if 0
+    /**
+      Toggle movie recording mode (FIXME - currently disabled)
+    */
+    void toggleRecordMode();
+#endif
 
     /**
-      Updates the state of the system based on the currently active mode
+      Toggle state rewind recording mode; this uses the RewindManager
+      for its functionality.
+    */
+    void toggleRewindMode();
+
+    /**
+      Updates the state of the system based on the currently active mode.
     */
     void update();
 
     /**
-      Load a state into the current system
+      Load a state into the current system.
 
       @param slot  The state 'slot' to load state from
     */
     void loadState(int slot = -1);
 
     /**
-      Save the current state from the system
+      Save the current state from the system.
 
       @param slot  The state 'slot' to save into
     */
     void saveState(int slot = -1);
 
     /**
-      Switches to the next higher state slot (circular queue style)
+      Switches to the next higher state slot (circular queue style).
     */
     void changeState();
 
@@ -92,7 +109,7 @@ class StateManager
     bool saveState(Serializer& out);
 
     /**
-      Resets manager to defaults
+      Resets manager to defaults.
     */
     void reset();
 
@@ -102,14 +119,6 @@ class StateManager
     RewindManager& rewindManager() const { return *myRewindManager; }
 
   private:
-    enum Mode {
-      kOffMode,
-      kMoviePlaybackMode,
-      kMovieRecordMode,
-      kRewindPlaybackMode,
-      kRewindRecordMode
-    };
-
     enum {
       kVersion = 001
     };

src/debugger/Debugger.cxx

@@ -505,12 +505,12 @@ void Debugger::setStartState()
 
   // If rewinding is not enabled, always start the debugger with a clean list
   RewindManager& r = myOSystem.state().rewindManager();
-  if(0) // FIXME
+  if(myOSystem.state().mode() == StateManager::Mode::Off)
     r.clear();
   myDialog->rewindButton().setEnabled(!r.empty());
 
   // Save initial state, but don't add it to the rewind list
-  saveOldState();  // FIXME - rework this
+  saveOldState();
 
   // Set the 're-disassemble' flag, but don't do it until the next scheduled time
   myDialog->rom().invalidate(false);

src/emucore/EventHandler.cxx

@@ -197,27 +197,20 @@ void EventHandler::poll(uInt64 time)
   {
     myOSystem.console().riot().update();
 
-#if 0
     // Now check if the StateManager should be saving or loading state
-    // Per-frame cheats are disabled if the StateManager is active, since
-    // it would interfere with proper playback
-    if(myOSystem.state().isActive())
-    {
+    // (for rewind and/or movies
+    if(myOSystem.state().mode() != StateManager::Mode::Off)
       myOSystem.state().update();
-    }
-    else
-#endif
-    {
-    #ifdef CHEATCODE_SUPPORT
-      for(auto& cheat: myOSystem.cheat().perFrame())
-        cheat->evaluate();
-    #endif
 
-      // Handle continuous snapshots
-      if(myContSnapshotInterval > 0 &&
-        (++myContSnapshotCounter % myContSnapshotInterval == 0))
-        takeSnapshot(uInt32(time) >> 10);  // not quite milliseconds, but close enough
-    }
+  #ifdef CHEATCODE_SUPPORT
+    for(auto& cheat: myOSystem.cheat().perFrame())
+      cheat->evaluate();
+  #endif
+
+    // Handle continuous snapshots
+    if(myContSnapshotInterval > 0 &&
+      (++myContSnapshotCounter % myContSnapshotInterval == 0))
+      takeSnapshot(uInt32(time) >> 10);  // not quite milliseconds, but close enough
   }
   else if(myOverlay)
   {
@@ -441,6 +434,10 @@ void EventHandler::handleKeyEvent(StellaKey key, StellaMod mod, bool state)
           myOSystem.frameBuffer().toggleFrameStats();
           break;
 
+        case KBDK_R:  // Alt-r toggles continuous store rewind states
+          myOSystem.state().toggleRewindMode();
+          break;
+
         case KBDK_S:
           if(myContSnapshotInterval == 0)
           {