Added preview tag to NotesLoaderBMS. Changed Song to check the preview file for sample length instead of the simfile if the preview file is set.

Docs/Changelog_sm5.txt

@@ -8,7 +8,7 @@ ________________________________________________________________________________
 ----------
 * [SelectMusic] Select Music now plays music file named by #PREVIEW tag if
   it's not blank, instead of using the song file for the sample music.  The
-  sample length from the simfile is used and the sample start is treated as
+  sample length is read from the preview file.  The sample start is treated as
   0. [kyzentun]
 * [Song] GetPreviewMusicPath added. [kyzentun]
 * [foreach] foreach_ordered lua function now works on tables that have both

src/NotesLoaderBMS.cpp

@@ -773,6 +773,7 @@ struct BMSChartInfo {
 	RString stageFile;
 	RString musicFile;
 	RString overrideMusicFile;
+	RString previewFile;
 
 	map<int, RString> backgroundChanges;
 };
@@ -894,6 +895,10 @@ void BMSChartReader::ReadHeaders()
 		{
 			info.overrideMusicFile = it->second;
 		}
+		else if (it->first == "#preview")
+		{
+			info.previewFile = it->second;
+		}
 		else if (it->first == "#offset")
 		{
 			out->m_Timing.m_fBeat0OffsetInSeconds = -StringToFloat(it->second);
@@ -1572,6 +1577,7 @@ void BMSSongLoader::AddToSong()
 		}
 
 		out->m_sMusicFile = main.info.musicFile;
+		out->m_PreviewFile= main.info.previewFile;
 		out->m_SongTiming = main.steps->m_Timing;
 	}
 

src/Song.cpp

@@ -575,6 +575,22 @@ void Song::TidyUpData( bool fromCache, bool /* duringCache */ )
 					 m_fMusicLengthSeconds);
 	}
 
+	if(!m_PreviewFile.empty())
+	{
+		RString error;
+		RageSoundReader* sample= RageSoundReader_FileReader::OpenFile(GetPreviewMusicPath(), error);
+		if(sample == NULL)
+		{
+			LOG->UserLog( "Preview file", GetPreviewMusicPath(), "couldn't be opened: %s", error.c_str() );
+			m_PreviewFile= "";
+		}
+		else
+		{
+			m_fMusicSampleLengthSeconds= sample->GetLength() / 1000.0f;
+			delete sample;
+		}
+	}
+
 	if( m_fMusicLengthSeconds < 0 )
 	{
 		LOG->UserLog("Sound file",