optimize rendering iteration

stepmania/src/NoteData.cpp

@@ -772,6 +772,21 @@ bool NoteData::GetPrevTapNoteRowForTrack( int track, int &rowInOut ) const
 	return true;
 }
 
+/* Return an iterator range.  This can be used to iterate trackwise over a range of
+ * notes.  It's like FOREACH_NONEMPTY_ROW_IN_TRACK_RANGE, except it only requires
+ * two map searches (iterating is O(1)), but the iterators will become invalid if
+ * the notes they represent disappear, so you need to pay attention to how you modify
+ * the data. */
+void NoteData::GetTapNoteRange( int iTrack, int iStartRow, int iEndRow, TrackMap::const_iterator &begin, TrackMap::const_iterator &end ) const
+{
+	ASSERT_M( iTrack < GetNumTracks(), ssprintf("%i,%i", iTrack, GetNumTracks())  );
+	ASSERT_M( iStartRow <= iEndRow, ssprintf("%i > %i", iStartRow, iEndRow)  );
+
+	const TrackMap &mapTrack = m_TapNotes[iTrack];
+	begin = mapTrack.lower_bound( iStartRow );
+	end = mapTrack.upper_bound( iEndRow );
+}
+
 bool NoteData::GetNextTapNoteRowForAllTracks( int &rowInOut ) const
 {
 	int iClosestNextRow = 999999;

stepmania/src/NoteData.h

@@ -21,9 +21,12 @@
 
 class NoteData
 {
+public:
+	typedef map<int,TapNote> TrackMap;
+
+private:
 	// There's no point in inserting empty notes into the map.
 	// Any blank space in the map is defined to be empty.
-	typedef map<int,TapNote> TrackMap;
 	vector<TrackMap> m_TapNotes;
 
 	vector<HoldNote>	m_HoldNotes;
@@ -60,6 +63,8 @@ public:
 	bool GetNextTapNoteRowForAllTracks( int &rowInOut ) const;
 	bool GetPrevTapNoteRowForTrack( int track, int &rowInOut ) const;
 	
+	void GetTapNoteRange( int iTrack, int iStartRow, int iEndRow, TrackMap::const_iterator &begin, TrackMap::const_iterator &end ) const;
+
 	void MoveTapNoteTrack( int dest, int src );
 	void SetTapNote( int track, int row, const TapNote& tn );
 	

stepmania/src/NoteField.cpp

@@ -605,9 +605,13 @@ void NoteField::DrawPrimitives()
 		NextDisplay = CurDisplay; ++NextDisplay;
 
 		// draw notes from furthest to closest
-		FOREACH_NONEMPTY_ROW_IN_TRACK_RANGE_REVERSE( *m_pNoteData, c, i, iFirstIndexToDraw, iLastIndexToDraw )
+
+		NoteData::TrackMap::const_iterator begin, end;
+		m_pNoteData->GetTapNoteRange( c, iFirstIndexToDraw, iLastIndexToDraw, begin, end );
+		for( ; begin != end; ++begin )
 		{	
-			const TapNote &tn = m_pNoteData->GetTapNote(c, i);
+			int i = begin->first;
+			const TapNote &tn = begin->second; //m_pNoteData->GetTapNote(c, i);
 			if( tn.type == TapNote::empty )	// no note here
 				continue;	// skip