Change: base autosaves intervals on real time (instead of game time) (#10655)

There are two fundamental issues with autosave:
- When fast-forwarding, it saves way too often
- When paused, it never saves

Both makes no sense. Autosaves are meant to prevent you from
accidentally losing your work. The emphasis on "your" work.

To solve both issues, the autosave now works on real time. You
can select every 10 / 30 / 60 / 120 minutes, which are similar to
what the setting was in game-months.

When you pause, autosaving will stop. Unless you make any change
to the game; then it will continue to make autosaves, even so
the game is paused. Unpausing / pausing resets this mechanism.

(cherry picked from commit f5fad88723)

src/openttd.cpp

@@ -90,6 +90,7 @@
 #include "scope_info.h"
 #include "network/network_survey.h"
 #include "timer/timer.h"
+#include "timer/timer_game_realtime.h"
 #include "timer/timer_game_tick.h"
 #include "network/network_sync.h"
 
@@ -1330,6 +1331,9 @@ void SwitchToMode(SwitchMode new_mode)
 	/* Make sure all AI controllers are gone at quitting game */
 	if (new_mode != SM_SAVE_GAME) AI::KillAll();
 
+	/* When we change mode, reset the autosave. */
+	if (new_mode != SM_SAVE_GAME) ChangeAutosaveFrequency(true);
+
 	/* Transmit the survey if we were in normal-mode and not saving. It always means we leaving the current game. */
 	if (_game_mode == GM_NORMAL && new_mode != SM_SAVE_GAME) _survey.Transmit(NetworkSurveyHandler::Reason::LEAVE);
 
@@ -2200,6 +2204,33 @@ static void DoAutosave()
 	DoAutoOrNetsave(GetAutoSaveFiosNumberedSaveName(), true, lt_counter);
 }
 
+/** Interval for regular autosaves. Initialized at zero to disable till settings are loaded. */
+static IntervalTimer<TimerGameRealtime> _autosave_interval({std::chrono::milliseconds::zero(), TimerGameRealtime::AUTOSAVE}, [](auto)
+{
+	/* We reset the command-during-pause mode here, so we don't continue
+	 * to make auto-saves when nothing more is changing. */
+	_pause_mode &= ~PM_COMMAND_DURING_PAUSE;
+
+	_do_autosave = true;
+	DoAutosave();
+	_do_autosave = false;
+	SetWindowDirty(WC_STATUS_BAR, 0);
+});
+
+/**
+ * Reset the interval of the autosave.
+ *
+ * If reset is not set, this does not set the elapsed time on the timer,
+ * so if the interval is smaller, it might result in an autosave being done
+ * immediately.
+ *
+ * @param reset Whether to reset the timer back to zero, or to continue.
+ */
+void ChangeAutosaveFrequency(bool reset)
+{
+	_autosave_interval.SetInterval({_settings_client.gui.autosave_realtime, TimerGameRealtime::AUTOSAVE}, reset);
+}
+
 /**
  * Request a new NewGRF scan. This will be executed on the next game-tick.
  * This is mostly needed to ensure NewGRF scans (which are blocking) are
@@ -2259,6 +2290,16 @@ void GameLoop()
 
 	if (unlikely(_check_special_modes)) GameLoopSpecial();
 
+	if (_game_mode == GM_NORMAL) {
+		static auto last_time = std::chrono::steady_clock::now();
+		auto now = std::chrono::steady_clock::now();
+		auto delta_ms = std::chrono::duration_cast<std::chrono::milliseconds>(now - last_time);
+		if (delta_ms.count() != 0) {
+			TimerManager<TimerGameRealtime>::Elapsed(delta_ms);
+			last_time = now;
+		}
+	}
+
 	/* switch game mode? */
 	if (_switch_mode != SM_NONE && !HasModalProgress()) {
 		SwitchToMode(_switch_mode);