Local time available without the clock instrument

Compute the local time value inside the TimeManager, so that the
UI doesn’t need to rely on the default clock instrument (which
might not exist) to show correct local time.

Also fix updating of time-offset/time-zone, to be based on distance
travelled instead of elapsed wall-clock time.

(needs an FGData update as well)

Ticket-Id: https://sourceforge.net/p/flightgear/codetickets/2514/

src/Time/TimeManager.cxx

@@ -25,7 +25,6 @@
 #include "TimeManager.hxx"
 
 #include <simgear/timing/sg_time.hxx>
-#include <simgear/structure/event_mgr.hxx>
 #include <simgear/misc/sg_path.hxx>
 #include <simgear/timing/lowleveltime.h>
 #include <simgear/structure/commands.hxx>
@@ -84,7 +83,7 @@ void TimeManager::init()
   _warp = fgGetNode("/sim/time/warp", true);
   _warp->addChangeListener(this);
   _maxFrameRate  = fgGetNode("/sim/frame-rate-throttle-hz", true);
-
+  _localTimeStringNode = fgGetNode("/sim/time/local-time-string", true);
   _warpDelta = fgGetNode("/sim/time/warp-delta", true);
   
   SGPath zone(globals->get_fg_root());
@@ -93,9 +92,6 @@ void TimeManager::init()
   _impl = new SGTime(globals->get_aircraft_position(), zone, _timeOverride->getLongValue());
   
   _warpDelta->setDoubleValue(0.0);
-  
-  globals->get_event_mgr()->addTask("updateLocalTime", this,
-                            &TimeManager::updateLocalTime, 30*60 );
   updateLocalTime();
   
   _impl->update(globals->get_aircraft_position(), _timeOverride->getLongValue(),
@@ -180,7 +176,6 @@ void TimeManager::shutdown()
   delete _impl;
   _impl = NULL;
   _inited = false;
-  globals->get_event_mgr()->removeTask("updateLocalTime");
 }
 
 void TimeManager::valueChanged(SGPropertyNode* aProp)
@@ -359,11 +354,18 @@ void TimeManager::update(double dt)
         _warp->setDoubleValue(_warp->getDoubleValue() + warpOffset);
     }
 
+    const auto d2 = distSqr(_lastTimeZoneCheckPosition, globals->get_aircraft_position_cart());
+    const auto oneNmSqr = SG_NM_TO_METER * SG_NM_TO_METER;
+    if (d2 > oneNmSqr) {
+        updateLocalTime();
+    }
+
   _lastClockFreeze = freeze;
   _impl->update(globals->get_aircraft_position(),
                _timeOverride->getLongValue(),
                _warp->getIntValue());
 
+  updateLocalTimeString();
   computeFrameRate();
 }
 
@@ -405,7 +407,26 @@ void TimeManager::throttleUpdateRate()
 // periodic time updater wrapper
 void TimeManager::updateLocalTime() 
 {
+    _lastTimeZoneCheckPosition = globals->get_aircraft_position_cart();
     _impl->updateLocal(globals->get_aircraft_position(), globals->get_fg_root() / "Timezone");
+    // synchronous update, since somebody might need that
+    updateLocalTimeString();
+}
+
+void TimeManager::updateLocalTimeString()
+{
+    time_t cur_time = _impl->get_cur_time();
+    struct tm* aircraftLocalTime = fgLocaltime(&cur_time, _impl->get_zonename());
+    static char buf[16];
+    snprintf(buf, 16, "%.2d:%.2d:%.2d",
+             aircraftLocalTime->tm_hour,
+             aircraftLocalTime->tm_min, aircraftLocalTime->tm_sec);
+
+    // check against current string to avoid changes all the time
+    const char* s = _localTimeStringNode->getStringValue();
+    if (strcmp(s, buf) != 0) {
+        _localTimeStringNode->setStringValue(buf);
+    }
 }
 
 void TimeManager::initTimeOffset()

src/Time/TimeManager.hxx

@@ -21,8 +21,9 @@
 #ifndef FG_TIME_TIMEMANAGER_HXX
 #define FG_TIME_TIMEMANAGER_HXX
 
-#include <simgear/structure/subsystem_mgr.hxx>
 #include <simgear/props/props.hxx>
+#include <simgear/structure/subsystem_mgr.hxx>
+#include <simgear/math/SGVec3.hxx>
 
 // forward decls
 class SGTime;
@@ -56,6 +57,7 @@ public:
     inline double getSteadyClockSec() const { return _steadyClock; }
 
     double getSimSpeedUpFactor() const;
+
 private:
     // test class is a friend so we can fake elapsed system time
     friend class TimeManagerTests;
@@ -73,6 +75,8 @@ private:
 
     void updateLocalTime();
 
+    void updateLocalTimeString();
+
     // set up a time offset (aka warp) if one is specified
     void initTimeOffset();
 
@@ -97,6 +101,7 @@ private:
     SGPropertyNode_ptr _computeDrift;
     SGPropertyNode_ptr _frameWait;
     SGPropertyNode_ptr _maxFrameRate;
+    SGPropertyNode_ptr _localTimeStringNode;
 
     bool _lastClockFreeze;
     bool _adjustWarpOnUnfreeze;
@@ -111,6 +116,9 @@ private:
     double _steadyClock;
     int _frameCount;
 
+    // we update TZ after moving more than a threshold distance
+    SGVec3d _lastTimeZoneCheckPosition;
+
     SGPropertyNode_ptr _sceneryLoaded;
     SGPropertyNode_ptr _modelHz;
     SGPropertyNode_ptr _timeDelta, _simTimeDelta;