Fix wrong lengths of exported tracks, when tracks have different lengths. (#5348)

* Fix wrong lengths of exported tracks, when tracks have different lengths.

Song::updateLength() was called in ProjectRenderer::run() after Song::startExport(),
updating m_length too late, resulting in it being used as the length of the wrong track.

* Fix "Export as loop" resetting after rendering the first track

Co-authored-by: Hyunjin Song <tteu.ingog@gmail.com>

src/core/ProjectRenderer.cpp

@@ -181,7 +181,6 @@ void ProjectRenderer::run()
 	PerfLogTimer perfLog("Project Render");
 
 	Engine::getSong()->startExport();
-	Engine::getSong()->updateLength();
 	// Skip first empty buffer.
 	Engine::mixer()->nextBuffer();
 

src/core/RenderManager.cpp

@@ -80,9 +80,9 @@ void RenderManager::renderNextTrack()
 		m_tracksToRender.pop_back();
 
 		// mute everything but the track we are about to render
-		for( auto it = m_unmuted.begin(); it != m_unmuted.end(); ++it )
+		for (auto track : m_unmuted)
 		{
-			(*it)->setMuted( (*it) != renderTrack );
+			track->setMuted(track != renderTrack);
 		}
 
 		// for multi-render, prefix each output file with a different number

src/core/Song.cpp

@@ -612,16 +612,14 @@ void Song::updateLength()
 {
 	m_length = 0;
 	m_tracksMutex.lockForRead();
-	for( TrackList::const_iterator it = tracks().begin();
-						it != tracks().end(); ++it )
+	for (auto track : tracks())
 	{
-		if( Engine::getSong()->isExporting() &&
-				( *it )->isMuted() )
+		if (m_exporting && track->isMuted())
 		{
 			continue;
 		}
 
-		const bar_t cur = ( *it )->length();
+		const bar_t cur = track->length();
 		if( cur > m_length )
 		{
 			m_length = cur;
@@ -744,6 +742,10 @@ void Song::stop()
 void Song::startExport()
 {
 	stop();
+
+	m_exporting = true;
+	updateLength();
+
 	if (m_renderBetweenMarkers)
 	{
 		m_exportSongBegin = m_exportLoopBegin = m_playPos[Mode_PlaySong].m_timeLine->loopBegin();
@@ -781,8 +783,6 @@ void Song::startExport()
 
 	playSong();
 
-	m_exporting = true;
-
 	m_vstSyncController.setPlaybackState( true );
 }
 
@@ -793,7 +793,6 @@ void Song::stopExport()
 {
 	stop();
 	m_exporting = false;
-	m_exportLoop = false;
 
 	m_vstSyncController.setPlaybackState( m_playing );
 }