notes exporter to osu for stepmania. yes this is my work with help of several people for getting the osu file format right.

gistfile1.cpp

#include "global.h"
#include "NoteTypes.h"
#include "NoteData.h"
#include "RageUtil.h"
#include "RageLog.h"
#include "RageFileManager.h"
#include "RageFile.h"
#include "NoteDataUtil.h"
#include "RageFile.h"
#include "Song.h"
#include "Steps.h"
#include "NotesWriterOsu.h"

static void WriteGlobalTags( RageFile &f, const Song &out, Steps* ToSave )
{
  f.PutLine("osu file format v11"); // double space
	
	f.PutLine("");

	f.PutLine("[General]");
	f.PutLine( ssprintf("AudioFilename: %s", out.m_sMusicFile.c_str()) );
	f.PutLine("AudioLeadIn: 1500");
	f.PutLine( ssprintf("PreviewTime: %.0f", out.m_fMusicSampleStartSeconds * 1000) );
	f.PutLine("Countdown: 0");
	f.PutLine("SampleSet: None");
	f.PutLine("StackLeniency: 0.7");
	f.PutLine("Mode: 3");
	f.PutLine("LetterboxInBreaks: 0");
	f.PutLine("");

	f.PutLine("[Editor]");
	f.PutLine("DistanceSnapping: 0.9");
	f.PutLine("BeatDivisor: 4");
	f.PutLine("GridSize: 16");
	f.PutLine("CurrentTime: 0");
	f.PutLine("");

	f.PutLine("[Metadata]");
	f.PutLine( ssprintf("Title: %s", out.m_sMainTitleTranslit.length() ? out.m_sMainTitleTranslit.c_str() : out.m_sMainTitle.c_str() ) );
	f.PutLine( ssprintf("TitleUnicode: %s", out.m_sMainTitle.c_str()) );
	f.PutLine( ssprintf("Artist: %s", out.m_sArtistTranslit.length() ? out.m_sArtistTranslit.c_str() : out.m_sArtist.c_str() ) );
	f.PutLine( ssprintf("ArtistUnicode: %s", out.m_sArtist.c_str()) );
	f.PutLine( ssprintf("Creator: %s", out.m_sCredit.length() ? out.m_sCredit.c_str() : "Stepmania 5" ) );
	f.PutLine( ssprintf("Version: %s", ToSave->GetChartName().c_str()) );
	f.PutLine( "Source: " );
	f.PutLine( "Tags: " );
	// fixme: what if we want to save the original .osu's beatmap IDs?
	// does it get updated automatically on osu's end?
	f.PutLine( "BeatmapID:0" );
	f.PutLine( "BeatmapSetID:-1");
	f.PutLine("");

	f.PutLine( "[Difficulty]" );
	f.PutLine( "HPDrainRate: 6" );
	f.PutLine( ssprintf("CircleSize: %i", ToSave->GetNoteData().GetNumTracks()) );
	f.PutLine( "OverallDifficulty: 5" );
	f.PutLine( "ApproachRate: 9" );
	f.PutLine( "SliderMultiplier: 1.4" );
	f.PutLine( "SliderTickRate: 1" );
	f.PutLine("");

	RString bgp = out.GetBackgroundPath().substr( 
		out.GetBackgroundPath().find_last_of("/") + 1,  // skip the / itself
		out.GetBackgroundPath().length() - out.GetBackgroundPath().find_last_of("/") );
	f.PutLine("[Events]");
	f.PutLine("// Background and Video events");
	f.PutLine( ssprintf("0,0,\"%s\"", bgp.c_str() ) );
	f.PutLine( "// Break Periods");
	f.PutLine("// Storyboard Layer 0 (Background)");
	f.PutLine("// Storyboard Layer 1 (Fail)");
	f.PutLine("// Storyboard Layer 2 (Pass)");
	f.PutLine("// Storyboard Layer 3 (Foreground)");
	f.PutLine("// Storyboard Sound Samples");
	 // todo: add autoplaykeysounds here
	f.PutLine("// Background Colour Transformations");
	f.PutLine("3,100,163,162,255");
	f.PutLine("");

	f.Flush();
}

static void WriteTimingData( RageFile &f, const Song &out, Steps* ToSave )
{
	const TimingData &timing = ToSave->m_Timing;
	
	f.PutLine("[TimingPoints]");
	
	// I assume these are sorted. It wouldn't be hard to sort them myself given the need.
	vector <TimingSegment*> segments = timing.GetTimingSegments(SEGMENT_BPM);
	vector <TimingSegment*> stopsegments = timing.GetTimingSegments(SEGMENT_STOP);
	vector <TimingSegment*> scrollsegments = timing.GetTimingSegments(SEGMENT_SCROLL);

	for (int i = 0; i < segments.size(); i++)
	{
		float time = timing.GetElapsedTimeFromBeat(segments.at(i)->GetBeat()) * 1000;
		float beatspace = 1000 / ((BPMSegment*)segments.at(i))->GetBPS();
		f.PutLine( ssprintf("%.0f,%.4f,4,1,0,15,1,0\n", 
    			   time, // time for this section
			       beatspace)
				 ); // 1000 / bps = ms per beat, what we need right here.
	}

	// it's kinda stupid to use stops if you can use speeds, assuming you're charting for osu!mania.
	// i don't recommend it, so restoring speed probably won't happen soon.
	for (int i = 0; i < stopsegments.size(); i++)
	{
		float time = timing.GetElapsedTimeFromBeat(stopsegments.at(i)->GetBeat()) * 1000;
		float sectionmultiplier = -100 / 0.1; // lol maths
		f.PutLine( ssprintf("%.0f,%.4f,4,1,0,15,0,0",
			time,
			sectionmultiplier) );

		// todo: check speeds and restore that.
		float stoptimefinish = time + ((StopSegment*)stopsegments.at(i))->GetPause() * 1000;
		f.PutLine( ssprintf("%.0f,%.4f,4,1,0,15,0,0",
			stoptimefinish,
			-100) );
	}

	// speeds (recommended way to approach o!m charting anyway) minimum value supported by osu is 0.1
	// maximum is like 10 or something.
	for (int i = 0; i < scrollsegments.size(); i++)
	{
		float time = timing.GetElapsedTimeFromBeat(scrollsegments.at(i)->GetBeat()) * 1000;
		float sectionmultiplier = -100 / ((ScrollSegment*)scrollsegments.at(i))->GetRatio(); // lol maths, again
		// it's kinda stupid that osu uses -100/x instead of x/-100 but hell if i know. it doesn't really matter.
		f.PutLine( ssprintf("%.0f,%.4f,4,1,0,15,0,0",
			time,
			sectionmultiplier) );
	}

	f.PutLine("");
	f.Flush();
}


static int TrackToXPos(int totaltracks, int track)
{
	double base = (512.0/totaltracks);
	double minus = (256.0/totaltracks);
	return (base * (track + 1) - minus);
}

static void WriteSteps( RageFile &f, const Song &out, Steps* ToSave )
{
	vector<NoteData> parts;
	float fLastBeat = -1.0f;
	const TimingData &timing = ToSave->m_Timing;
	float PendingTracks[16]; // For hold notes.

	for (int i = 0; i < 16; i++)
	{
		PendingTracks[i] = 0;
	}

	NoteDataUtil::SplitCompositeNoteData( ToSave->GetNoteData(), parts );

	FOREACH( NoteData, parts, nd )
	{
		NoteDataUtil::InsertHoldTails( *nd );
		fLastBeat = max( fLastBeat, nd->GetLastBeat() );
	}

	int iLastMeasure = int( fLastBeat/4 );

	f.PutLine("[HitObjects]");
	
	FOREACH( NoteData, parts, nd )
	{
		for( int m = 0; m <= iLastMeasure; ++m ) // foreach measure
		{
			NoteType nt = NoteDataUtil::GetSmallestNoteTypeForMeasure( *nd, m );
			int iRowSpacing;
			if( nt == NoteType_Invalid )
				iRowSpacing = 1;
			else
				iRowSpacing = lrintf( NoteTypeToBeat(nt) * ROWS_PER_BEAT );

			const int iMeasureStartRow = m * 192;
			const int iMeasureLastRow = (m+1) * 192 - 1;

			for( int r=iMeasureStartRow; r<=iMeasureLastRow; r+=iRowSpacing )
			{
				for( int t = 0; t < nd->GetNumTracks(); ++t )
				{
					const TapNote &tn = nd->GetTapNote(t, r);
					char c;
					int xpos = TrackToXPos(nd->GetNumTracks(), t);
					float ftiming = timing.GetElapsedTimeFromBeat(NoteRowToBeat(r)) * 1000;

					switch( tn.type )
					{
					case TapNote::tap: // x, y, time, notetype, hitsound, whatever whatever whatever.
						f.PutLine( ssprintf("%i,192,%.0f,1,0,0:0:0", xpos, ftiming) );
						break;
					case TapNote::hold_head:
						PendingTracks[t] = timing.GetElapsedTimeFromBeat(NoteRowToBeat(r)) * 1000;
						break;
					case TapNote::hold_tail:
						f.PutLine( 
							ssprintf("%d,0,%.0f,128,0,%.0f,1:0:0\n", 
							TrackToXPos(nd->GetNumTracks(), t), 
							PendingTracks[t], 
							timing.GetElapsedTimeFromBeat(NoteRowToBeat(r)) * 1000
							));
					} // switch (tn.type)
				} // for t=0..
			} // for r=0..
		} // for m = 0
	} // foreach.. 
	f.Flush();
}

bool NotesWriterOSU::Write( const Song &out, const vector<Steps*>& vpStepsToSave )
{
	int flags = RageFile::WRITE;
	int totalSteps = vpStepsToSave.size();
	

	// ragefiles can't be vector'd :V -az
	RageFile f;
	
	for (int i = 0; i < totalSteps; i++)
	{
		RString filename = out.GetSongDir() + out.GetDisplayArtist() + " - " + // directory/artist - title [difficulty].osu
			out.GetDisplayMainTitle() + " [" + 
			vpStepsToSave.at(i)->GetChartName() + "].osu";

		if( !f.Open(filename, flags ) )
		{
			LOG->UserLog( "Song file", filename, "couldn't be opened for writing: %s", f.GetError().c_str() );
			return false;
		}
		WriteGlobalTags(f, out, vpStepsToSave.at(i));
		WriteTimingData(f, out, vpStepsToSave.at(i));
		WriteSteps(f, out, vpStepsToSave.at(i));

		f.Close();
	}

	return true;

}

gistfile2.cpp

#ifndef NOTES_WRITER_OSU_H
#define NOTES_WRITER_OSU_H

class Song;
/** @brief Writes a Song to a .DWI file. */
namespace NotesWriterOSU
{
	/**
	 * @brief Write the song out to a file.
	 * @param sPath the path to write the file.
	 * @param out the Song to be written out.
	 * @return its success or failure. */
	bool Write( const Song &out, const vector<Steps*>& vpStepsToSave );
}

#endif