Cherry pick live scrubbing from master

src/comm/LogReplayLink.cc

@@ -14,6 +14,7 @@
 
 #include <QFileInfo>
 #include <QtEndian>
+#include <QSignalSpy>
 
 const char*  LogReplayLinkConfiguration::_logFilenameKey = "logFilename";
 
@@ -378,7 +379,7 @@ void LogReplayLink::_readNextLogEntry(void)
             timeToNextExecutionMSecs = desiredPacedTimeMSecs - currentTimeMSecs;
         }
 
-        emit currentLogTimeSecs((_logCurrentTimeUSecs - _logStartTimeUSecs) / 1000000);
+        _signalCurrentLogTimeSecs();
 
         // And schedule the next execution of this function.
         _readTickTimer.start(timeToNextExecutionMSecs);
@@ -460,9 +461,13 @@ void LogReplayLink::_resetPlaybackToBeginning(void)
 void LogReplayLink::movePlayhead(int percentComplete)
 {
     if (isPlaying()) {
-        qWarning() << "Should not move playhead while playing, pause first";
+        _pauseOnThread();
+        QSignalSpy waitForPause(this, SIGNAL(playbackPaused));
+        waitForPause.wait();
+        if (_readTickTimer.isActive()) {
             return;
         }
+    }
 
     if (percentComplete < 0 || percentComplete > 100) {
         qWarning() << "Bad percentage value" << percentComplete;
@@ -505,6 +510,7 @@ void LogReplayLink::movePlayhead(int percentComplete)
         // And scan until we reach the start of a MAVLink message. We make sure to record this timestamp for
         // smooth jumping around the file.
         _logCurrentTimeUSecs = _seekToNextMavlinkMessage(&dummy);
+        _signalCurrentLogTimeSecs();
 
         // Now update the UI with our actual final position.
         newRelativeTimeUSecs = (float)(_logCurrentTimeUSecs - _logStartTimeUSecs);
@@ -571,3 +577,8 @@ void LogReplayLink::_playbackError(void)
     _logFile.close();
     emit playbackError();
 }
+
+void LogReplayLink::_signalCurrentLogTimeSecs(void)
+{
+    emit currentLogTimeSecs((_logCurrentTimeUSecs - _logStartTimeUSecs) / 1000000);
+}

src/comm/LogReplayLink.h

@@ -121,6 +121,7 @@ private:
     void _finishPlayback(void);
     void _playbackError(void);
     void _resetPlaybackToBeginning(void);
+    void _signalCurrentLogTimeSecs(void);
 
     // Virtuals from LinkInterface
     virtual bool _connect(void);

src/ui/QGCMAVLinkLogPlayer.cc

@@ -142,7 +142,6 @@ void QGCMAVLinkLogPlayer::_playbackStarted(void)
     _enablePlaybackControls(true);
     _ui->playButton->setChecked(true);
     _ui->playButton->setIcon(QIcon(":/res/Pause"));
-    _ui->positionSlider->setEnabled(false);
 }
 
 /// Signalled from LogReplayLink when replay is paused
@@ -150,7 +149,6 @@ void QGCMAVLinkLogPlayer::_playbackPaused(void)
 {
     _ui->playButton->setIcon(QIcon(":/res/Play"));
     _ui->playButton->setChecked(false);
-    _ui->positionSlider->setEnabled(true);
 }
 
 void QGCMAVLinkLogPlayer::_playbackPercentCompleteChanged(int percentComplete)

src/ui/QGCMAVLinkLogPlayer.ui

@@ -75,7 +75,7 @@
       <number>100</number>
      </property>
      <property name="tracking">
-      <bool>false</bool>
+      <bool>true</bool>
      </property>
      <property name="orientation">
       <enum>Qt::Horizontal</enum>