new-session-manager/Timeline/Timeline.C

/*******************************************************************************/
/* Copyright (C) 2008 Jonathan Moore Liles                                     */
/*                                                                             */
/* This program is free software; you can redistribute it and/or modify it     */
/* under the terms of the GNU General Public License as published by the       */
/* Free Software Foundation; either version 2 of the License, or (at your      */
/* option) any later version.                                                  */
/*                                                                             */
/* This program is distributed in the hope that it will be useful, but WITHOUT */
/* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or       */
/* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for   */
/* more details.                                                               */
/*                                                                             */
/* You should have received a copy of the GNU General Public License along     */
/* with This program; see the file COPYING.  If not,write to the Free Software */
/* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
/*******************************************************************************/

#include "Timeline.H"
#include "Tempo_Sequence.H"
#include "Time_Sequence.H"
#include "Audio_Sequence.H"
#include "Control_Sequence.H"
#include <FL/Fl_Scrollbar.H>

#include "Ruler_Sequence.H"

// #include <FL/Fl_Image.H>
// #include <FL/Fl_RGB_Image.H> // needed for alpha blending

#include "Track.H"

bool Timeline::draw_with_measure_lines = true;

const float UPDATE_FREQ = 0.02f;


#include "Playback_DS.H"
#include "Record_DS.H"

#include "Transport.H"

void
Timeline::cb_scroll ( Fl_Widget *w, void *v )
{
    ((Timeline*)v)->cb_scroll( w );
}

void
Timeline::cb_scroll ( Fl_Widget *w )
{
    if ( w == vscroll )
    {
        tracks->position( tracks->x(), (rulers->y() + rulers->h()) - vscroll->value() );

        yposition( vscroll->value() );

        int rh = h() - rulers->h();

        vscroll->value( vscroll->value(), 30, 0, max( tracks->h() - rh, rh) );
    }
    else
    {
        if ( hscroll->zoom_changed() )
        {
            _fpp = hscroll->zoom() * 1;

            int maxx = ts_to_x( _length );
            hscroll->range( 0, maxx );

            redraw();
        }
        else
        {
            xposition( hscroll->value() );
        }
    }
}


Timeline::Timeline ( int X, int Y, int W, int H, const char* L ) : Fl_Overlay_Window( X, Y, W, H, L )
{

    box( FL_FLAT_BOX );
    xoffset = 0;

    X = Y = 0;

    p1 = p2 = 0;

    {
        Scalebar *o = new Scalebar( X, Y + H - 18, W - 18, 18 );

        o->range( 0, 48000 * 300 );
        o->zoom_range( 2, 8192 );
        o->zoom( 256 );
        o->type( FL_HORIZONTAL );
        o->callback( cb_scroll, this );

        hscroll = o;
    }

    {
        Fl_Scrollbar *o = new Fl_Scrollbar( X + W - 18, Y, 18, H - 18 );

        o->type( FL_VERTICAL );
        o->callback( cb_scroll, this );
        vscroll = o;
    }

    {
        Fl_Pack *o = new Fl_Pack( X + Track::width(), Y, (W - Track::width()) - vscroll->w(), H - hscroll->h(), "rulers" );
        o->type( Fl_Pack::VERTICAL );

        {
            Tempo_Sequence *o = new Tempo_Sequence( 0, 0, 800, 24 );

            o->color( FL_RED );

            o->label( "Tempo" );
            o->align( FL_ALIGN_LEFT );

            tempo_track = o;
        }

        {
            Time_Sequence *o = new Time_Sequence( 0, 24, 800, 24 );

            o->color( fl_color_average( FL_RED, FL_WHITE, 0.50f ) );

            o->label( "Time" );
            o->align( FL_ALIGN_LEFT );

            time_track = o;
        }

        {
            Ruler_Sequence *o = new Ruler_Sequence( 0, 24, 800, 24 );

            o->color( FL_GREEN );

            o->label( "Ruler" );
            o->align( FL_ALIGN_LEFT );

            ruler_track = o;
        }

        o->size( o->w(), o->child( 0 )->h() * o->children() );
        rulers = o;
        o->end();
    }


    {
        _sample_rate = 44100;
        _fpp = 256;
        _length = _sample_rate * 60 * 2;

        {
            Fl_Pack *o = new Fl_Pack( X, rulers->y() + rulers->h(), W - vscroll->w(), 5000 );
            o->type( Fl_Pack::VERTICAL );
            o->spacing( 0 );

            tracks = o;
            o->end();
            resizable( o );
        }
    }


    /* make sure scrollbars are on top */
    add( vscroll );
    add( hscroll );

    vscroll->range( 0, tracks->h() );

    redraw();

    end();

    Fl::add_timeout( UPDATE_FREQ, update_cb, this );

}


float
Timeline::beats_per_minute ( nframes_t when ) const
{
    return tempo_track->beats_per_minute( when );
}

int
Timeline::beats_per_bar ( nframes_t when ) const
{
    time_sig t = time_track->time( when );

    return t.beats_per_bar;
}

void
Timeline::beats_per_minute ( nframes_t when, float bpm )
{
    tempo_track->add( new Tempo_Point( when, bpm ) );
}

#if 0
struct BBT
{
    int bar, beat, tick;

    BBT ( int bar, int beat, int tick ) : bar( bar ), beat( beat ), tick( tick )
        {
        }
};

/** returns the BBT value for timestamp /when/ by examining the tempo/time maps */
BBT
Timeline::bbt ( nframes_t when )
{
    Tempo_Sequence *tempo = (Tempo_Sequence*)rulers->child( 0 );

    BBT bbt;

    for ( list <Sequence_Widget *>::const_iterator i = tempo.widgets.begin();
          i != tempo.widgets.end(); ++i )
    {
        Tempo_Point *p = *i;

    }



};
#endif

/** return the absolute pixel of the nearest measure line to /x/ */
int
Timeline::nearest_line ( int ix )
{
    for ( int x = ix - 10; x < ix + 10; ++x )
    {
        const int measure = ts_to_x( (double)(_sample_rate * 60) / beats_per_minute( x_to_ts( x - Track::width() ) + xoffset ));

//        const int abs_x = ts_to_x( xoffset ) + x;

        if ( 0 == x % measure )
            return x;
    }

    return -1;
}

/** draw appropriate measure lines inside the given bounding box */
/* FIXME: this function *really* needs to be optimized. Currently it
   searched both the time and tempo lists once for every horiontal
   pixel and performs a number of calculations--this is slow. */
void
Timeline::draw_measure ( int X, int Y, int W, int H, Fl_Color color, bool BBT )
{
    if ( ! draw_with_measure_lines )
        return;

//    fl_line_style( FL_DASH, 2 );
    fl_line_style( FL_DASH, 0 );

    Fl_Color beat = fl_color_average( FL_BLACK, color, 0.65f );
    Fl_Color bar  = fl_color_average( FL_RED, color, 0.65f );

    int measure;

    for ( int x = X; x < X + W; ++x )
    {

        measure = ts_to_x( (double)(_sample_rate * 60) / beats_per_minute( x_to_ts( x - Track::width() ) + xoffset ) );

        const int abs_x = ts_to_x( xoffset ) + x - Track::width();

        if ( 0 == abs_x % measure )
        {
            int bpb = beats_per_bar( x_to_ts( x -Track::width() ) + xoffset );

            if ( 0 == (abs_x / measure) % bpb )
            {
                if ( measure * bpb < 8 )
                    break;

                if ( BBT )
                {
                    fl_font( FL_HELVETICA, 14 );

                    fl_color( fl_lighter( color ) );

                    char pat[40];

                    const nframes_t ts = x_to_ts( abs_x );

//                    if ( draw_hms )
                    {

                        const double seconds = (double)ts / _sample_rate;

                        int S = (int)seconds;
                        int M = S / 60; S -= M * 60;
                        int H = M / 60; M -= H * 60;

                        snprintf( pat, sizeof( pat ), "%d:%d:%d", H, M, S );
                    }
//                    else if ( draw_bbt )
                    {

/*                         const int bar = */
/*                         const int beat; */
/*                         const int tick = 0; */

/*                         snprintf( pat, sizeof( pat ), "%d:%d:%d", bar, beat, tick ); */
                    }


                    fl_draw( pat, x, Y + 14 );
                }

                fl_color( bar );
            }
            else
            {
                if ( measure < 8 )
                    continue;

                fl_color( beat );
            }


            fl_line( x, Y, x, Y + H );
        }

    }
    fl_line_style( FL_SOLID, 0 );

}

void
Timeline::draw_measure_lines ( int X, int Y, int W, int H, Fl_Color color )
{
    draw_measure( X, Y, W, H, color, false );
}

/** just like draw mesure lines except that it also draws the BBT values.  */
void
Timeline::draw_measure_BBT ( int X, int Y, int W, int H, Fl_Color color )
{
    draw_measure( X, Y, W, H, color, true );
}

void
Timeline::xposition ( int X )
{
//    _old_xposition = xoffset;

    xoffset = x_to_ts( X );

    damage( FL_DAMAGE_SCROLL );
}

void
Timeline::yposition ( int Y )
{
//    _old_yposition = _yposition;

    _yposition = Y;

    damage( FL_DAMAGE_SCROLL );
}

void
Timeline::draw_clip ( void * v, int X, int Y, int W, int H )
{
    Timeline *tl = (Timeline *)v;

//            printf( "draw_clip: %d,%d %dx%d\n", X, Y, W, H );
    fl_push_clip( X, Y, W, H );

    fl_color( rand() );
    fl_rectf( X, Y, X + W, Y + H );


    tl->draw_child( *tl->rulers );

    /* headers */
    fl_push_clip( tl->tracks->x(), tl->rulers->y() + tl->rulers->h(), Track::width(), tl->h() - tl->rulers->h()  - tl->hscroll->h() );
    tl->draw_child( *tl->tracks );
    fl_pop_clip();

    /* track bodies */
    fl_push_clip( tl->tracks->x() + Track::width(), tl->rulers->y() + tl->rulers->h(), tl->tracks->w() - Track::width(), tl->h() - tl->rulers->h()  - tl->hscroll->h() );
    tl->draw_child( *tl->tracks );
    fl_pop_clip();

//    tl->draw_child( *tl->tracks );

    fl_pop_clip();
}


// static unsigned char *rect_image;

void
Timeline::resize ( int X, int Y, int W, int H )
{
    Fl_Overlay_Window::resize( X, Y, W, H );

    /* why is this necessary? */
    rulers->resize( Track::width(), 0, W - Track::width() - vscroll->w(), rulers->h() );

    /* why is THIS necessary? */
    hscroll->resize( 0, H - 18, hscroll->w(), 18 );
    vscroll->size( vscroll->w(), H - 18 );
}

void
Timeline::draw ( void )
{
    int X, Y, W, H;

    int bdx = 0;
    int bdw = 0;

    X = tracks->x() + bdx + 1;
    Y = tracks->y();
    W = tracks->w() - bdw - 1;
    H = tracks->h();

/*     if ( damage() & FL_DAMAGE_USER1 ) */
/*     { */

/*         /\* save the rectangle so we can draw it (darkened) in the overlay *\/ */
/*         Rectangle &r = _selection; */
/*         make_current(); */
/*         rect_image = fl_read_image( NULL, r.x, r.y, r.w, r.h, 0 ); */

/*         return; */
/*     } */

    if ( (damage() & FL_DAMAGE_ALL)
         ||
         damage() & FL_DAMAGE_EXPOSE )
    {
        draw_box( box(), 0, 0, w(), h(), color() );

        fl_push_clip( 0, rulers->y(), w(), rulers->h() );
        draw_child( *rulers );
        fl_pop_clip();

        fl_push_clip( tracks->x(), rulers->y() + rulers->h(), tracks->w(), hscroll->y() - (rulers->y() + rulers->h()) );
        draw_child( *tracks );
        fl_pop_clip();

        draw_child( *hscroll );
        draw_child( *vscroll );

        redraw_overlay();


/*     Rectangle &r = _selection; */

/*     unsigned char *data = fl_read_image( NULL, r.x, r.y, r.w, r.h, 0 ); */

/*     Fl_RGB_Image bi( data, r.w, r.h, 3 ); */

/*     bi.color_average( FL_BLACK, 0.50f ); */

/*     bi.draw( r.x, r.y ); */

/*     delete[] data; */


/*     if ( r.w && r.h ) */
/*     { */
/*     const unsigned char data[] = { 0, 127, 0, 96, */
/*                                    0, 96, 0, 127 }; */
/*     Fl_RGB_Image bi( data, 2, 2, 2 ); */

/*     Fl_Image *bi2 = bi.copy( r.w, r.h ); */

/*     bi2->draw( r.x, r.y ); */

/*     delete bi2; */
/*     } */

        return;
    }

    if ( damage() & FL_DAMAGE_CHILD )
    {
        fl_push_clip( rulers->x(), rulers->y(), rulers->w(), rulers->h() );
        update_child( *rulers );
        fl_pop_clip();

        fl_push_clip( tracks->x(), rulers->y() + rulers->h(), tracks->w(), hscroll->y() - (rulers->y() + rulers->h()) );
        update_child( *tracks );
        fl_pop_clip();

        update_child( *hscroll );
        update_child( *vscroll );
    }


    if ( damage() & FL_DAMAGE_SCROLL )
    {
        int dx = ts_to_x( _old_xposition ) - ts_to_x( xoffset );
        int dy = _old_yposition - _yposition;

        if ( ! dy )
            fl_scroll( rulers->x(), rulers->y(), rulers->w(), rulers->h(), dx, 0, draw_clip, this );

        Y = rulers->y() + rulers->h();
        H = h() - rulers->h() - hscroll->h();

        if ( dy == 0 )
            fl_scroll( X + Track::width(), Y, W - Track::width(), H, dx, dy, draw_clip, this );
        else
            fl_scroll( X, Y, W, H, dx, dy, draw_clip, this );

        _old_xposition = xoffset;
        _old_yposition = _yposition;

    }

}

void
Timeline::draw_cursor ( nframes_t frame, Fl_Color color )
{
    int x = ( ts_to_x( frame ) - ts_to_x( xoffset ) ) + tracks->x() + Track::width();

    if ( x < tracks->x() + Track::width() || x > tracks->x() + tracks->w() )
        return;

    fl_color( color );

    int y = rulers->y() + rulers->h();
    int h = this->h() - hscroll->h();

    fl_push_clip( Track::width(), y, tracks->w(), h );

    fl_line( x, y, x, h );

    fl_color( fl_darker( color ) );

    fl_line( x - 1, y, x - 1, h );

    fl_color( FL_BLACK );

    fl_line( x + 1, y, x + 1, h );

    /* draw cap */
    fl_color( color );
    fl_begin_polygon();

    fl_vertex( x - 8, y );
    fl_vertex( x, y + 8 );
    fl_vertex( x + 8, y );

    fl_end_polygon();


    /* draw cap outline */
    fl_color( FL_BLACK );
    fl_begin_line();

    fl_vertex( x - 8, y );
    fl_vertex( x, y + 8 );
    fl_vertex( x + 8, y );

    fl_end_line();

    fl_pop_clip();

}

void
Timeline::draw_playhead ( void )
{
    if ( p1 != p2 )
    {
        draw_cursor( p1, FL_BLUE );
        draw_cursor( p2, FL_GREEN );
    }

    draw_cursor( transport->frame, FL_RED );
}

void
Timeline::redraw_playhead ( void )
{
    static nframes_t last_playhead = -1;

    if ( last_playhead != transport->frame )
    {
        redraw_overlay();
        last_playhead = transport->frame;
    }
}


/** called so many times a second to redraw the playhead etc.  */
void
Timeline::update_cb ( void *arg )
{
    Fl::repeat_timeout( UPDATE_FREQ, update_cb, arg );

    Timeline *tl = (Timeline *)arg;

    tl->redraw_playhead();
}

void
Timeline::draw_overlay ( void )
{

    draw_playhead();

    if ( ! ( _selection.w && _selection.h ) )
        return;

    fl_push_clip( tracks->x() + Track::width(), rulers->y() + rulers->h(),  tracks->w() - Track::width(), h() - rulers->h() - hscroll->h() );

    const Rectangle &r = _selection;

    fl_color( FL_BLACK );

    fl_line_style( FL_SOLID, 2 );

    fl_rect( r.x + 2, r.y + 2, r.w, r.h );
    fl_color( FL_MAGENTA );
    fl_line_style( FL_DASH, 2 );
    fl_rect( r.x, r.y, r.w, r.h );

    fl_line( r.x, r.y, r.x + r.w, r.y + r.h );

    fl_line( r.x + r.w, r.y, r.x, r.y + r.h );

/*     fl_overlay_rect( r.x, r.y, r.w, r.h ); */

    fl_line_style( FL_SOLID, 0 );


/*     const unsigned char data[] = { 127, 127, 127, 96, */
/*                                    127, 96, 127, 40 }; */
/*     Fl_RGB_Image bi( data, 2, 2, 2 ); */

/*     Fl_Image *bi2 = bi.copy( r.w, r.h ); */

/*     bi2->draw( r.x, r.y ); */

/*     delete bi2; */


/*     unsigned char *data = fl_read_image( NULL, r.x, r.y, r.w, r.h, 0 ); */



/*     Fl_RGB_Image bi( rect_image, r.w, r.h, 3 ); */

/*     bi.color_average( FL_BLACK, 0.50f ); */

/*     bi.draw( r.x, r.y ); */

/*     delete[] rect_image; */
/*     rect_image = NULL; */

    fl_pop_clip();

}

// #include "Sequence_Widget.H"

/** select all widgets in inside rectangle /r/ */
void
Timeline::select( const Rectangle &r )
{
    const int Y = r.y;

    for ( int i = tracks->children(); i-- ; )
    {
        Track *t = (Track*)tracks->child( i );

        if ( ! ( t->y() > Y + r.h || t->y() + t->h() < Y ) )
            t->track()->select_range( r.x, r.w );
    }
}

int
Timeline::handle ( int m )
{
    static Drag *drag = NULL;

    switch ( m )
    {
        case FL_KEYBOARD:
        {
            switch ( Fl::event_key() )
            {
                case FL_Delete:
                {
                    Sequence_Widget::delete_selected();

                    return 1;
                }

/*                 case FL_Home: */
/*                     transport->locate( 0 ); */
/*                     return 1; */
/*                 case ' ': */
/*                     transport->toggle(); */
/*                     return 1; */

                case 'p':
                {
                    int X = Fl::event_x() - Track::width();

                    if ( X > 0 )
                    {
                        transport->locate( xoffset + x_to_ts( X ) );
                    }

                    return 1;
                }
                case '[':
                {
                    int X = Fl::event_x() - Track::width();

                    if ( X > 0 )
                    {
                        p1 = xoffset + x_to_ts( X );
                    }

                    return 1;
                }
                case ']':
                {
                    int X = Fl::event_x() - Track::width();

                    if ( X > 0 )
                    {
                        p2 = xoffset + x_to_ts( X );
                    }

                    return 1;
                }
                default:
                    return Fl_Overlay_Window::handle( m );
            }

            return 0;
        }
        default:
        {
            int r = Fl_Overlay_Window::handle( m );

            if ( m != FL_RELEASE && r )
                return r;

            const int X = Fl::event_x();
            const int Y = Fl::event_y();

            switch ( m )
            {
                case FL_PUSH:
                {
                    take_focus();

                    if ( Fl::event_button1() )
                    {
                        assert( ! drag );

                        drag = new Drag( X - x(), Y - y() );
                        _selection.x = drag->x;
                        _selection.y = drag->y;
                    }
                    else if ( Fl::event_button3() )
                    {
                        Fl_Menu_Item menu[] =
                            {
                                { "Add Track",        0, 0, 0, FL_SUBMENU    },
                                { "Audio",           0, 0, 0 },
                                { 0 },
                                { 0 },
                            };

                        const Fl_Menu_Item *r = menu->popup( X, Y, "Timeline" );

                        if ( r == &menu[1] )
                        {
                            /* FIXME: prompt for I/O config? */

                            Loggable::block_start();

                            /* add audio track */
                            char *name = get_unique_track_name( "Audio" );

                            Track *t = new Track( name );

                            Sequence *o = new Audio_Sequence( t );
                            new Control_Sequence( t );

                            add_track( t );

                            t->track( o );

/*                             t->add( new Control_Sequence( t  ); */

                            t->color( (Fl_Color)rand() );

                            Loggable::block_end();
                        }

                    }
                    else
                        return 0;

                    break;
                }
                case FL_DRAG:
                {
                    int ox = X - drag->x;
                    int oy = Y - drag->y;

                    if ( ox < 0 )
                        _selection.x = X;
                    if ( oy < 0 )
                        _selection.y = Y;

                    _selection.w = abs( ox );
                    _selection.h = abs( oy );
                    break;
                }
                case FL_RELEASE:
                {
                    delete drag;
                    drag = NULL;

                    select( _selection );

                    _selection.w = _selection.h = 0;
                    break;
                }
                default:
                    return 0;
                    break;
            }

            redraw_overlay();
            return 1;
        }
    }

}


void
Timeline::zoom_in ( void )
{
    hscroll->zoom_in();
}

void
Timeline::zoom_out ( void )
{
    hscroll->zoom_out();
}

/** zoom the display to show /secs/ seconds per screen */
void
Timeline::zoom ( float secs )
{
    const int sw = w() - vscroll->w() - Track::width();

    /* FIXME: we actually need to set this in the scalebar */
    _fpp = (int)((secs * _sample_rate) / sw);

    redraw();
}

Track *
Timeline::track_by_name ( const char *name )
{
    for ( int i = tracks->children(); i-- ; )
    {
        Track *t = (Track*)tracks->child( i );

        if ( ! strcmp( name, t->name() ) )
            return t;
    }

    return NULL;
}

char *
Timeline::get_unique_track_name ( const char *name )
{
    char pat[256];

    strcpy( pat, name );

    for ( int i = 1; track_by_name( pat ); ++i )
        snprintf( pat, sizeof( pat ), "%s.%d", name, i );

    return strdup( pat );
}

void
Timeline::add_track ( Track *track )
{
    printf( "added new track to the timeline\n" );
    /* FIXME: do locking */
    tracks->add( track );

    /* FIXME: why is this necessary? doesn't the above add do DAMAGE_CHILD? */
    redraw();

}

void
Timeline::remove_track ( Track *track )
{
    printf( "removed track from the timeline\n" );

    /* FIXME: do locking */

    /* FIXME: what to do about track contents? */
    tracks->remove( track );

    /* FIXME: why is this necessary? doesn't the above add do DAMAGE_CHILD? */
    redraw();
}

/** Initiate recording for all armed tracks */
bool
Timeline::record ( void )
{
    Loggable::block_start();

    for ( int i = tracks->children(); i-- ; )
    {
        Track *t = (Track*)tracks->child( i );

        if ( t->armed() && t->record_ds )
            t->record_ds->start( transport->frame );
    }

    deactivate();

    return true;
}

/** stop recording for all armed tracks */
void
Timeline::stop ( void )
{
    for ( int i = tracks->children(); i-- ; )
    {
        Track *t = (Track*)tracks->child( i );

        if ( t->armed() && t->record_ds )
            t->record_ds->stop( transport->frame );
    }

    Loggable::block_end();

    activate();
}


/**********/
/* Engine */
/**********/

/** call process() on each track header */
nframes_t
Timeline::process ( nframes_t nframes )
{
    for ( int i = tracks->children(); i-- ; )
    {
        Track *t = (Track*)tracks->child( i );

        t->process( nframes );
    }

    /* FIXME: BOGUS */
    return nframes;
}

/* THREAD: RT */
void
Timeline::seek ( nframes_t frame )
{
    for ( int i = tracks->children(); i-- ; )
    {
        Track *t = (Track*)tracks->child( i );

        t->seek( frame );
    }
}

/* THREAD: RT */
int
Timeline::seek_pending ( void )
{
    int r = 0;

    for ( int i = tracks->children(); i-- ; )
    {
        Track *t = (Track*)tracks->child( i );

        if ( t->playback_ds )
            r += t->playback_ds->buffer_percent() < 50;
    }

    return r;
}


/* FIXME: shouldn't these belong to the engine? */
int
Timeline::total_input_buffer_percent ( void )
{
    int r = 0;

    int cnt = 0;

    for ( int i = tracks->children(); i-- ; )
    {
        Track *t = (Track*)tracks->child( i );

        if ( t->record_ds )
        {
            ++cnt;
            r += t->record_ds->buffer_percent();
        }
    }

    if ( ! cnt )
        return 0;

    return r / cnt;
}

int
Timeline::total_output_buffer_percent ( void )
{

    int r = 0;

    int cnt = 0;

    for ( int i = tracks->children(); i-- ; )
    {
        Track *t = (Track*)tracks->child( i );

        if ( t->playback_ds )
        {
            ++cnt;
            r += t->playback_ds->buffer_percent();
        }
    }

    if ( ! cnt )
        return 0;

    return r / cnt;
}