More rewrites of iterations over channels...

... that can generalize to more than stereo

src/Project.cpp

@@ -2051,25 +2051,6 @@ void AudacityProject::FixScrollbars()
          GetTrackPanel()->HandleCursorForPresentMouseState(); } );
 }
 
-std::shared_ptr<Track> AudacityProject::GetFirstVisible()
-{
-   std::shared_ptr<Track> pTrack;
-   if (GetTracks()) {
-      TrackListIterator iter(GetTracks());
-      for (Track *t = iter.First(); t; t = iter.Next()) {
-         int y = t->GetY();
-         int h = t->GetHeight();
-         if (y + h - 1 >= mViewInfo.vpos) {
-            // At least the bottom row of pixels is not scrolled away above
-            pTrack = Track::Pointer(t);
-            break;
-         }
-      }
-   }
-
-   return pTrack;
-}
-
 void AudacityProject::UpdateLayout()
 {
    if (!mTrackPanel)
@@ -4232,23 +4213,35 @@ AudacityProject::AddImportedTracks(const wxString &fileName,
    bool initiallyEmpty = mTracks->empty();
    double newRate = 0;
    wxString trackNameBase = fileName.AfterLast(wxFILE_SEP_PATH).BeforeLast('.');
-   bool isLinked = false;
    int i = -1;
-   for (auto &uNewTrack : newTracks) {
-      ++i;
 
+   // Must add all tracks first (before using Track::IsLeader)
+   for (auto &uNewTrack : newTracks) {
       auto newTrack = mTracks->Add(std::move(uNewTrack));
       results.push_back(Track::Pointer(newTrack));
+   }
+   newTracks.clear();
+      
+   // Now name them
+
+   // Add numbers to track names only if there is more than one (mono or stereo)
+   // track (not necessarily, more than one channel)
+   const bool useSuffix =
+      make_iterator_range( results.begin() + 1, results.end() )
+         .any_of( []( decltype(*results.begin()) &pTrack )
+            { return pTrack->IsLeader(); } );
+
+   for (const auto &newTrack : results) {
+      if ( newTrack->IsLeader() )
+         // Count groups only
+         ++i;
+
       newTrack->SetSelected(true);
-      //we need to check link status based on the first channel only.
+
-      if(0==i)
+      if ( useSuffix )
-         isLinked = newTrack->GetLinked();
-      if (numTracks > 2 || (numTracks > 1 && !isLinked) ) {
          newTrack->SetName(trackNameBase + wxString::Format(wxT(" %d" ), i + 1));
-      }
+      else
-      else {
          newTrack->SetName(trackNameBase);
-      }
 
       newTrack->TypeSwitch( [&](WaveTrack *wt) {
          if (newRate == 0)
@@ -4299,8 +4292,6 @@ AudacityProject::AddImportedTracks(const wxString &fileName,
    // Moved this call to higher levels to prevent flicker redrawing everything on each file.
    //   HandleResize();
 
-   newTracks.clear();
-
    return results;
 }
 

src/Project.h

@@ -213,8 +213,6 @@ class AUDACITY_DLL_API AudacityProject final : public wxFrame,
    const ViewInfo &GetViewInfo() const { return mViewInfo; }
    ViewInfo &GetViewInfo() { return mViewInfo; }
 
-   std::shared_ptr<Track> GetFirstVisible();
-
    void GetPlayRegion(double* playRegionStart, double *playRegionEnd);
    bool IsPlayRegionLocked() { return mLockPlayRegion; }
    void SetPlayRegionLocked(bool value) { mLockPlayRegion = value; }

src/TrackArtist.cpp

@@ -341,7 +341,6 @@ void TrackArtist::SetMargins(int left, int top, int right, int bottom)
 
 void TrackArtist::DrawTracks(TrackPanelDrawingContext &context,
                              const TrackList * tracks,
-                             Track * start,
                              const wxRegion & reg,
                              const wxRect & rect,
                              const wxRect & clip,
@@ -351,13 +350,11 @@ void TrackArtist::DrawTracks(TrackPanelDrawingContext &context,
                              bool bigPoints,
                              bool drawSliders)
 {
+   // Copy the horizontal extent of rect; will later change only the vertical.
    wxRect trackRect = rect;
-   wxRect stereoTrackRect;
-   TrackListConstIterator iter(tracks);
-   const Track *t;
 
    bool hasSolo = false;
-   for (t = iter.First(); t; t = iter.Next()) {
+   for (const Track *t : *tracks) {
       t = t->SubstitutePendingChangedTrack().get();
       auto pt = dynamic_cast<const PlayableTrack *>(t);
       if (pt && pt->GetSolo()) {
@@ -381,15 +378,23 @@ void TrackArtist::DrawTracks(TrackPanelDrawingContext &context,
 
    gPrefs->Read(wxT("/GUI/ShowTrackNameInWaveform"), &mbShowTrackNameInWaveform, false);
 
-   t = iter.StartWith(start);
+   for(auto leader : tracks->Leaders()) {
-   while (t) {
+      auto group = TrackList::Channels( leader );
-      t = t->SubstitutePendingChangedTrack().get();
+      leader = leader->SubstitutePendingChangedTrack().get();
-      trackRect.y = t->GetY() - zoomInfo.vpos;
-      trackRect.height = t->GetHeight();
 
-      if (trackRect.y > clip.GetBottom() && !t->GetLinked()) {
+      trackRect.y = leader->GetY() - zoomInfo.vpos;
+      trackRect.height = group.sum( [&] (const Track *channel) {
+         channel = channel->SubstitutePendingChangedTrack().get();
+         return channel->GetHeight();
+      });
+
+      if (trackRect.GetBottom() < clip.GetTop())
+         continue;
+      else if (trackRect.GetTop() > clip.GetBottom())
          break;
-      }
+
+      for (auto t : group) {
+         t = t->SubstitutePendingChangedTrack().get();
 
 #if defined(DEBUG_CLIENT_AREA)
          // Filled rectangle to show the interior of the client area
@@ -400,8 +405,6 @@ void TrackArtist::DrawTracks(TrackPanelDrawingContext &context,
          dc.DrawRectangle(zr);
 #endif
 
-      stereoTrackRect = trackRect;
-
          // For various reasons, the code will break if we display one
          // of a stereo pair of tracks but not the other - for example,
          // if you try to edit the envelope of one track when its linked
@@ -410,20 +413,7 @@ void TrackArtist::DrawTracks(TrackPanelDrawingContext &context,
          // its linked partner, and see if any part of that rect is on-screen.
          // If so, we draw both.  Otherwise, we can safely draw neither.
 
-      Track *link = t->GetLink();
+         if (trackRect.Intersects(clip) && reg.Contains(trackRect)) {
-      if (link) {
-         if (t->GetLinked()) {
-            // If we're the first track
-            stereoTrackRect.height += link->GetHeight();
-         }
-         else {
-            // We're the second of two
-            stereoTrackRect.y -= link->GetHeight();
-            stereoTrackRect.height += link->GetHeight();
-         }
-      }
-
-      if (stereoTrackRect.Intersects(clip) && reg.Contains(stereoTrackRect)) {
             wxRect rr = trackRect;
             rr.x += mMarginLeft;
             rr.y += mMarginTop;
@@ -433,8 +423,7 @@ void TrackArtist::DrawTracks(TrackPanelDrawingContext &context,
                       selectedRegion, zoomInfo,
                       drawEnvelope, bigPoints, drawSliders, hasSolo);
          }
-
+      }
-      t = iter.Next();
    }
 }
 
@@ -480,8 +469,7 @@ void TrackArtist::DrawTrack(TrackPanelDrawingContext &context,
    #endif
 
          if (mbShowTrackNameInWaveform &&
-             // Exclude right channel of stereo track 
+             wt->IsLeader() &&
-             !(!wt->GetLinked() && wt->GetLink()) &&
              // Exclude empty name.
              !wt->GetName().IsEmpty()) {
             wxBrush Brush;

src/TrackArtist.h

@@ -55,7 +55,7 @@ class AUDACITY_DLL_API TrackArtist {
 
    void SetColours(int iColorIndex);
    void DrawTracks(TrackPanelDrawingContext &context,
-                   const TrackList *tracks, Track *start,
+                   const TrackList *tracks,
                    const wxRegion & reg,
                    const wxRect & rect, const wxRect & clip,
                    const SelectedRegion &selectedRegion, const ZoomInfo &zoomInfo,

src/TrackPanel.cpp

@@ -1156,8 +1156,7 @@ void TrackPanel::DrawTracks(wxDC * dc)
    TrackPanelDrawingContext context{ *dc, Target(), mLastMouseState };
 
    // The track artist actually draws the stuff inside each track
-   auto first = GetProject()->GetFirstVisible();
+   mTrackArtist->DrawTracks(context, GetTracks(),
-   mTrackArtist->DrawTracks(context, GetTracks(), first.get(),
                             region, tracksRect, clip,
                             mViewInfo->selectedRegion, *mViewInfo,
                             envelopeFlag, bigPointsFlag, sliderFlag);
@@ -1847,14 +1846,12 @@ void TrackPanel::UpdateTrackVRuler(const Track *t)
    wxRect rect(GetVRulerOffset(),
             kTopMargin,
             GetVRulerWidth(),
-            t->GetHeight() - (kTopMargin + kBottomMargin));
+            0);
 
-   mTrackArtist->UpdateVRuler(t, rect);
+
-   const Track *l = t->GetLink();
+   for (auto channel : TrackList::Channels(t)) {
-   if (l)
+      rect.height = channel->GetHeight() - (kTopMargin + kBottomMargin);
-   {
+      mTrackArtist->UpdateVRuler(channel, rect);
-      rect.height = l->GetHeight() - (kTopMargin + kBottomMargin);
-      mTrackArtist->UpdateVRuler(l, rect);
    }
 }
 
@@ -2080,30 +2077,29 @@ wxRect TrackPanel::FindTrackRect( const Track * target, bool label )
       return { 0, 0, 0, 0 };
    }
 
-   wxRect rect{
-      0,
-      target->GetY() - mViewInfo->vpos,
-      GetSize().GetWidth(),
-      target->GetHeight()
-   };
-
    // PRL:  I think the following very old comment misused the term "race
    // condition" for a bug that happened with only a single thread.  I think the
    // real problem referred to, was that this function could be reached, via
    // TrackPanelAx callbacks, during low-level operations while the TrackList
-   // was not in a consistent state.  Therefore GetLinked() did not imply
+   // was not in a consistent state.
-   // that GetLink() was not null.
    // Now the problem is fixed by delaying the handling of events generated
-   // by TrackList.
+   // by TrackList.  And besides that, we use Channels() instead of looking
+   // directly at the links.
 
    // Old comment:
    // The check for a null linked track is necessary because there's
    // a possible race condition between the time the 2 linked tracks
    // are added and when wxAccessible methods are called.  This is
    // most evident when using Jaws.
-   if (target->GetLinked() && target->GetLink()) {
+   auto height = TrackList::Channels( target ).sum( &Track::GetHeight );
-      rect.height += target->GetLink()->GetHeight();
+
-   }
+   wxRect rect{
+      0,
+      target->GetY() - mViewInfo->vpos,
+      GetSize().GetWidth(),
+      height
+   };
+
 
    rect.x += kLeftMargin;
    if (label)
@@ -2151,8 +2147,7 @@ void TrackPanel::SetFocusedCell()
 void TrackPanel::SetFocusedTrack( Track *t )
 {
    // Make sure we always have the first linked track of a stereo track
-   if (t && !t->GetLinked() && t->GetLink())
+   t = *GetTracks()->FindLeader(t);
-      t = (WaveTrack*)t->GetLink();
 
    auto cell = mAx->SetFocus( Track::Pointer( t ) ).get();
 
@@ -2657,7 +2652,7 @@ TrackPanelCellIterator &TrackPanelCellIterator::operator++ ()
    }
    if ( mpTrack ) {
       if ( mType == CellType::Label &&
-           mpTrack->GetLink() && !mpTrack->GetLinked() )
+           !mpTrack->IsLeader() )
          // Visit label of stereo track only once
          ++mType;
       switch ( mType ) {
@@ -2723,10 +2718,10 @@ void TrackPanelCellIterator::UpdateRect()
             mRect.x = kLeftMargin;
             mRect.width = kTrackInfoWidth - mRect.x;
             mRect.y += kTopMargin;
+            mRect.height =
+               TrackList::Channels(mpTrack.get())
+                  .sum( &Track::GetHeight );
             mRect.height -= (kBottomMargin + kTopMargin);
-            auto partner = mpTrack->GetLink();
-            if ( partner && mpTrack->GetLinked() )
-               mRect.height += partner->GetHeight();
             break;
          }
          case CellType::VRuler:
@@ -2742,11 +2737,12 @@ void TrackPanelCellIterator::UpdateRect()
             // The resizer region encompasses the bottom margin proper to this
             // track, plus the top margin of the next track (or, an equally
             // tall zone below, in case there is no next track)
-            auto partner = mpTrack->GetLink();
+            if ( mpTrack.get() ==
-            if ( partner && mpTrack->GetLinked() )
+                *TrackList::Channels(mpTrack.get()).rbegin() )
-               mRect.x = kTrackInfoWidth;
+               // Last channel has a resizer extending farther leftward
-            else
                mRect.x = kLeftMargin;
+            else
+               mRect.x = kTrackInfoWidth;
             mRect.width -= (mRect.x + kRightMargin);
             mRect.y += (mRect.height - kBottomMargin);
             mRect.height = (kBottomMargin + kTopMargin);

src/TrackPanelAx.cpp

@@ -144,13 +144,9 @@ bool TrackPanelAx::IsFocused( const Track *track )
    if (origTrack)
       track = origTrack;
 
-   if( ( track == focusedTrack.get() ) ||
+   return focusedTrack
-       ( focusedTrack && track == focusedTrack->GetLink() ) )
+      ? TrackList::Channels(focusedTrack.get()).contains(track)
-   {
+      : !track;
-      return true;
-   }
-
-   return false;
 }
 
 int TrackPanelAx::TrackNum( const std::shared_ptr<Track> &target )

src/tracks/playabletrack/wavetrack/ui/CutlineHandle.cpp

@@ -143,8 +143,6 @@ UIHandle::Result CutlineHandle::Click
 
    // Cutline data changed on either branch, so refresh the track display.
    UIHandle::Result result = RefreshCell;
-   // Assume linked track is wave or null
-   const auto linked = static_cast<WaveTrack*>(mpTrack->GetLink());
 
    if (event.LeftDown())
    {
@@ -156,26 +154,30 @@ UIHandle::Result CutlineHandle::Click
 
          // When user presses left button on cut line, expand the line again
          double cutlineStart = 0, cutlineEnd = 0;
+         double *pCutlineStart = &cutlineStart, *pCutlineEnd = &cutlineEnd;
 
-         mpTrack->ExpandCutLine(mLocation.pos, &cutlineStart, &cutlineEnd);
+         for (auto channel :
-
+              TrackList::Channels(mpTrack.get())) {
-         if (linked)
+            channel->ExpandCutLine(
-            // Expand the cutline in the opposite channel if it is present.
+               mLocation.pos, pCutlineStart, pCutlineEnd);
-            linked->ExpandCutLine(mLocation.pos);
+            if ( channel == mpTrack.get() )
+               pCutlineStart = pCutlineEnd = nullptr;
+         }
 
          viewInfo.selectedRegion.setTimes(cutlineStart, cutlineEnd);
          result |= UpdateSelection;
       }
       else if (mLocation.typ == WaveTrackLocation::locationMergePoint) {
          const double pos = mLocation.pos;
-         mpTrack->MergeClips(mLocation.clipidx1, mLocation.clipidx2);
+         for (auto channel :
-
+              TrackList::Channels(mpTrack.get())) {
-         if (linked) {
             // Don't assume correspondence of merge points across channels!
-            int idx = FindMergeLine(linked, pos);
+            int idx = FindMergeLine(channel, pos);
             if (idx >= 0) {
-               WaveTrack::Location location = linked->GetCachedLocations()[idx];
+               WaveTrack::Location location =
-               linked->MergeClips(location.clipidx1, location.clipidx2);
+                  channel->GetCachedLocations()[idx];
+               channel->MergeClips(
+                  location.clipidx1, location.clipidx2);
             }
          }
 
@@ -184,10 +186,10 @@ UIHandle::Result CutlineHandle::Click
    }
    else if (event.RightDown())
    {
-      bool removed = mpTrack->RemoveCutLine(mLocation.pos);
+      bool removed = false;
-
+      for (auto channel :
-      if (linked)
+           TrackList::Channels(mpTrack.get()))
-         removed = linked->RemoveCutLine(mLocation.pos) || removed;
+         removed = channel->RemoveCutLine(mLocation.pos) || removed;
 
       if (!removed)
          // Nothing happened, make no Undo item

src/tracks/playabletrack/wavetrack/ui/WaveTrackControls.cpp

@@ -213,14 +213,9 @@ void WaveColorMenuTable::OnWaveColorChange(wxCommandEvent & event)
    int newWaveColor = id - OnInstrument1ID;
 
    AudacityProject *const project = ::GetActiveProject();
-//   TrackList *const tracks = project->GetTracks();
 
-   pTrack->SetWaveColorIndex(newWaveColor);
+   for (auto channel : TrackList::Channels(pTrack))
-
+      channel->SetWaveColorIndex(newWaveColor);
-   // Assume partner is wave or null
-   const auto partner = static_cast<WaveTrack*>(pTrack->GetLink());
-   if (partner)
-      partner->SetWaveColorIndex(newWaveColor);
 
    project->PushState(wxString::Format(_("Changed '%s' to %s"),
       pTrack->GetName(),
@@ -336,12 +331,9 @@ void FormatMenuTable::OnFormatChange(wxCommandEvent & event)
       return; // Nothing to do.
 
    AudacityProject *const project = ::GetActiveProject();
-   pTrack->ConvertToSampleFormat(newFormat);
 
-   // Assume partner is wave or null
+   for (auto channel : TrackList::Channels(pTrack))
-   const auto partner = static_cast<WaveTrack*>(pTrack->GetLink());
+      channel->ConvertToSampleFormat(newFormat);
-   if (partner)
-      partner->ConvertToSampleFormat(newFormat);
 
    /* i18n-hint: The strings name a track and a format */
    project->PushState(wxString::Format(_("Changed '%s' to %s"),
@@ -439,11 +431,9 @@ int RateMenuTable::IdOfRate(int rate)
 void RateMenuTable::SetRate(WaveTrack * pTrack, double rate)
 {
    AudacityProject *const project = ::GetActiveProject();
-   pTrack->SetRate(rate);
+   for (auto channel : TrackList::Channels(pTrack))
-   // Assume linked track is wave or null
+      channel->SetRate(rate);
-   const auto partner = static_cast<WaveTrack*>(pTrack->GetLink());
+
-   if (partner)
-      partner->SetRate(rate);
    // Separate conversion of "rate" enables changing the decimals without affecting i18n
    wxString rateString = wxString::Format(wxT("%.3f"), rate);
    /* i18n-hint: The string names a track */
@@ -733,20 +723,11 @@ void WaveTrackMenuTable::OnSetDisplay(wxCommandEvent & event)
       (id == WaveTrack::Waveform &&
       pTrack->GetWaveformSettings().isLinear() != linear);
    if (wrongType || wrongScale) {
-      pTrack->SetLastScaleType();
+      for (auto channel : TrackList::Channels(pTrack)) {
-      pTrack->SetDisplay(WaveTrack::WaveTrackDisplay(id));
+         channel->SetLastScaleType();
+         channel->SetDisplay(WaveTrack::WaveTrackDisplay(id));
          if (wrongScale)
-         pTrack->GetIndependentWaveformSettings().scaleType = linear
+            channel->GetIndependentWaveformSettings().scaleType = linear
-         ? WaveformSettings::stLinear
-         : WaveformSettings::stLogarithmic;
-
-      // Assume partner is wave or null
-      auto partner = static_cast<WaveTrack *>(pTrack->GetLink());
-      if (partner) {
-         partner->SetLastScaleType();
-         partner->SetDisplay(WaveTrack::WaveTrackDisplay(id));
-         if (wrongScale)
-            partner->GetIndependentWaveformSettings().scaleType = linear
                ? WaveformSettings::stLinear
                : WaveformSettings::stLogarithmic;
       }

src/tracks/playabletrack/wavetrack/ui/WaveTrackSliderHandles.cpp

@@ -47,12 +47,9 @@ UIHandle::Result GainSliderHandle::SetValue
    auto pTrack = GetWaveTrack();
 
    if (pTrack) {
-      pTrack->SetGain(newValue);
+      for (auto channel :
-
+           TrackList::Channels(pTrack.get()))
-      // Assume linked track is wave or null
+         channel->SetGain(newValue);
-      const auto link = static_cast<WaveTrack*>(mpTrack.lock()->GetLink());
-      if (link)
-         link->SetGain(newValue);
 
       MixerBoard *const pMixerBoard = pProject->GetMixerBoard();
       if (pMixerBoard)
@@ -131,12 +128,9 @@ UIHandle::Result PanSliderHandle::SetValue(AudacityProject *pProject, float newV
    auto pTrack = GetWaveTrack();
 
    if (pTrack) {
-      pTrack->SetPan(newValue);
+      for (auto channel :
-
+           TrackList::Channels(pTrack.get()))
-      // Assume linked track is wave or null
+         channel->SetPan(newValue);
-      const auto link = static_cast<WaveTrack*>(pTrack->GetLink());
-      if (link)
-         link->SetPan(newValue);
 
       MixerBoard *const pMixerBoard = pProject->GetMixerBoard();
       if (pMixerBoard)

src/tracks/playabletrack/wavetrack/ui/WaveTrackVRulerControls.cpp

@@ -58,13 +58,12 @@ void WaveTrackVRulerControls::DoZoomPreset( int i)
 
    const auto wt = static_cast<WaveTrack*>(pTrack.get());
 
-   // Don't pass the partner, that causes problems when updating display
+   // Don't do all channels, that causes problems when updating display
    // during recording and there are special pending tracks.
    // This function implements WaveTrack::DoSetMinimized which is always
    // called in a context that loops over linked tracks too and reinvokes.
-   auto partner = nullptr;
    WaveTrackVZoomHandle::DoZoom(
-         NULL, wt, partner, (i==1)?kZoomHalfWave: kZoom1to1,
+         NULL, wt, false, (i==1)?kZoomHalfWave: kZoom1to1,
          wxRect(0,0,0,0), 0,0, true);
 }
 
@@ -88,9 +87,7 @@ unsigned WaveTrackVRulerControls::HandleWheelRotation
    wxASSERT(pTrack->GetKind() == Track::Wave);
    auto steps = evt.steps;
 
-   const auto wt = static_cast<WaveTrack*>(pTrack.get());
+   WaveTrack *const wt = static_cast<WaveTrack*>(pTrack.get());
-   // Assume linked track is wave or null
-   const auto partner = static_cast<WaveTrack*>(wt->GetLink());
    const bool isDB =
       wt->GetDisplay() == WaveTrack::Waveform &&
       wt->GetWaveformSettings().scaleType == WaveformSettings::stLogarithmic;
@@ -102,24 +99,20 @@ unsigned WaveTrackVRulerControls::HandleWheelRotation
       if (!(min < 0.0 && max > 0.0))
          return RefreshNone;
 
-      WaveformSettings &settings = wt->GetIndependentWaveformSettings();
+      WaveformSettings &settings =
+         wt->GetIndependentWaveformSettings();
       float olddBRange = settings.dBRange;
+      for (auto channel : TrackList::Channels(wt)) {
+         WaveformSettings &channelSettings =
+            channel->GetIndependentWaveformSettings();
          if (steps < 0)
             // Zoom out
-         settings.NextLowerDBRange();
+            channelSettings.NextLowerDBRange();
          else
-         settings.NextHigherDBRange();
+            channelSettings.NextHigherDBRange();
-      float newdBRange = settings.dBRange;
-
-      if (partner) {
-         WaveformSettings &settings = partner->GetIndependentWaveformSettings();
-         if (steps < 0)
-            // Zoom out
-            settings.NextLowerDBRange();
-         else
-            settings.NextHigherDBRange();
       }
 
+      float newdBRange = settings.dBRange;
 
       // Is y coordinate within the rectangle half-height centered about
       // the zero level?
@@ -135,19 +128,16 @@ unsigned WaveTrackVRulerControls::HandleWheelRotation
          const float extreme = (LINEAR_TO_DB(2) + newdBRange) / newdBRange;
          max = std::min(extreme, max * olddBRange / newdBRange);
          min = std::max(-extreme, min * olddBRange / newdBRange);
-         wt->SetLastdBRange();
+         for (auto channel : TrackList::Channels(wt)) {
-         wt->SetDisplayBounds(min, max);
+            channel->SetLastdBRange();
-         if (partner) {
+            channel->SetDisplayBounds(min, max);
-            partner->SetLastdBRange();
-            partner->SetDisplayBounds(min, max);
          }
       }
    }
    else if (event.CmdDown() && !event.ShiftDown()) {
       const int yy = event.m_y;
-      const auto partner = static_cast<WaveTrack *>(wt);
       WaveTrackVZoomHandle::DoZoom(
-         pProject, wt, partner, (steps < 0)?kZoomOut:kZoomIn,
+         pProject, wt, true, (steps < 0)?kZoomOut:kZoomIn,
          evt.rect, yy, yy, true);
    }
    else if (!event.CmdDown() && event.ShiftDown()) {
@@ -173,9 +163,8 @@ unsigned WaveTrackVRulerControls::HandleWheelRotation
             std::min(bound,
                      numberScale.PositionToValue(numberScale.ValueToPosition(newBottom) + 1.0f));
 
-         wt->SetSpectrumBounds(newBottom, newTop);
+         for (auto channel : TrackList::Channels(wt))
-         if (partner)
+            channel->SetSpectrumBounds(newBottom, newTop);
-            partner->SetSpectrumBounds(newBottom, newTop);
       }
       else {
          float topLimit = 2.0;
@@ -191,9 +180,8 @@ unsigned WaveTrackVRulerControls::HandleWheelRotation
          float newTop = std::min(topLimit, top + delta);
          const float newBottom = std::max(bottomLimit, newTop - range);
          newTop = std::min(topLimit, newBottom + range);
-         wt->SetDisplayBounds(newBottom, newTop);
+         for (auto channel : TrackList::Channels(wt))
-         if (partner)
+            channel->SetDisplayBounds(newBottom, newTop);
-            partner->SetDisplayBounds(newBottom, newTop);
       }
    }
    else

src/tracks/playabletrack/wavetrack/ui/WaveTrackVZoomHandle.cpp

@@ -65,11 +65,12 @@ void WaveTrackVZoomHandle::Enter(bool)
 // the zoomKind and cause a drag-zoom-in.
 void WaveTrackVZoomHandle::DoZoom
    (AudacityProject *pProject,
-    WaveTrack *pTrack, WaveTrack *partner, int ZoomKind,
+    WaveTrack *pTrack, bool allChannels, int ZoomKind,
     const wxRect &rect, int zoomStart, int zoomEnd,
     bool fixedMousePoint)
 {
    static const float ZOOMLIMIT = 0.001f;
+
    int height = rect.height;
    int ypos = rect.y;
 
@@ -318,15 +319,13 @@ void WaveTrackVZoomHandle::DoZoom
    }
 
    // Now actually apply the zoom.
-   if (spectral) {
+   for (auto channel : TrackList::Channels(pTrack)) {
-      pTrack->SetSpectrumBounds(min, max);
+      if (!allChannels && channel != pTrack)
-      if (partner)
+         continue;
-         partner->SetSpectrumBounds(min, max);
+      if (spectral)
-   }
+         channel->SetSpectrumBounds(min, max);
-   else {
+      else
-      pTrack->SetDisplayBounds(min, max);
+         channel->SetDisplayBounds(min, max);
-      if (partner)
-         partner->SetDisplayBounds(min, max);
    }
 
    zoomEnd = zoomStart = 0;
@@ -389,10 +388,8 @@ void WaveTrackVRulerMenuTable::InitMenu(Menu *, void *pUserData)
 
 void WaveTrackVRulerMenuTable::OnZoom( int iZoomCode )
 {
-   // Assume linked track is wave or null
-   const auto partner = static_cast<WaveTrack *>(mpData->pTrack->GetLink());
    WaveTrackVZoomHandle::DoZoom
-      (::GetActiveProject(), mpData->pTrack, partner,
+      (::GetActiveProject(), mpData->pTrack, true,
        iZoomCode, mpData->rect, mpData->yy, mpData->yy, false);
 
    using namespace RefreshCode;
@@ -467,17 +464,17 @@ void WaveformVRulerMenuTable::OnWaveformScaleType(wxCommandEvent &evt)
 {
    WaveTrack *const wt = mpData->pTrack;
    // Assume linked track is wave or null
-   const auto partner = static_cast<WaveTrack*>(wt->GetLink());
    const WaveformSettings::ScaleType newScaleType =
       WaveformSettings::ScaleType(
          std::max(0,
             std::min((int)(WaveformSettings::stNumScaleTypes) - 1,
                evt.GetId() - OnFirstWaveformScaleID
       )));
+
    if (wt->GetWaveformSettings().scaleType != newScaleType) {
-      wt->GetIndependentWaveformSettings().scaleType = newScaleType;
+      for (auto channel : TrackList::Channels(wt)) {
-      if (partner)
+         channel->GetIndependentWaveformSettings().scaleType = newScaleType;
-         partner->GetIndependentWaveformSettings().scaleType = newScaleType;
+      }
 
       ::GetActiveProject()->ModifyState(true);
 
@@ -540,8 +537,7 @@ END_POPUP_MENU()
 void SpectrumVRulerMenuTable::OnSpectrumScaleType(wxCommandEvent &evt)
 {
    WaveTrack *const wt = mpData->pTrack;
-   // Assume linked track is wave or null
+
-   const auto partner = static_cast<WaveTrack*>(wt->GetLink());
    const SpectrogramSettings::ScaleType newScaleType =
       SpectrogramSettings::ScaleType(
          std::max(0,
@@ -549,9 +545,8 @@ void SpectrumVRulerMenuTable::OnSpectrumScaleType(wxCommandEvent &evt)
                evt.GetId() - OnFirstSpectrumScaleID
       )));
    if (wt->GetSpectrogramSettings().scaleType != newScaleType) {
-      wt->GetIndependentSpectrogramSettings().scaleType = newScaleType;
+      for (auto channel : TrackList::Channels(wt))
-      if (partner)
+         channel->GetIndependentSpectrogramSettings().scaleType = newScaleType;
-         partner->GetIndependentSpectrogramSettings().scaleType = newScaleType;
 
       ::GetActiveProject()->ModifyState(true);
 
@@ -678,8 +673,7 @@ UIHandle::Result WaveTrackVZoomHandle::Release
       if( bVZoom ){
          if( shiftDown )
             mZoomStart=mZoomEnd;
-         const auto partner = static_cast<WaveTrack *>(pTrack->GetLink());
+         DoZoom(pProject, pTrack.get(), true,
-         DoZoom(pProject, pTrack.get(), partner,
                 shiftDown ? (rightUp ? kZoom1to1 : kZoomOut)  : kZoomIn,
             mRect, mZoomStart, mZoomEnd, !shiftDown);
       }

src/tracks/playabletrack/wavetrack/ui/WaveTrackVZoomHandle.h

@@ -42,7 +42,7 @@ public:
 
    static void DoZoom
    (AudacityProject *pProject,
-    WaveTrack *pTrack, WaveTrack *partner, int ZoomKind,
+    WaveTrack *pTrack, bool allChannels, int ZoomKind,
     const wxRect &rect, int zoomStart, int zoomEnd,
     bool fixedMousePoint);
 

src/tracks/ui/EnvelopeHandle.cpp

@@ -178,6 +178,8 @@ UIHandle::Result EnvelopeHandle::Click
    const ViewInfo &viewInfo = pProject->GetViewInfo();
    const auto pTrack = static_cast<Track*>(evt.pCell.get());
 
+   mEnvelopeEditors.clear();
+
    unsigned result = Cancelled;
    if (pTrack)
       result = pTrack->TypeSwitch< decltype(RefreshNone) >(
@@ -191,18 +193,21 @@ UIHandle::Result EnvelopeHandle::Click
          mLog = !wt->GetWaveformSettings().isLinear();
          wt->GetDisplayBounds(&mLower, &mUpper);
          mdBRange = wt->GetWaveformSettings().dBRange;
-         mEnvelopeEditor =
+         auto channels = TrackList::Channels( wt );
-            std::make_unique< EnvelopeEditor >( *mEnvelope, true );
+         for ( auto channel : channels ) {
-         mEnvelopeEditorRight.reset();
+            if (channel == wt)
-
+               mEnvelopeEditors.push_back(
-         // Assume linked track is wave or null
+                  std::make_unique< EnvelopeEditor >( *mEnvelope, true ) );
-         auto partner = static_cast<WaveTrack*>(wt->GetLink());
+            else {
-         if (partner)
+               auto e2 = channel->GetEnvelopeAtX(event.GetX());
-         {
+               if (e2)
-            auto clickedEnvelope = partner->GetEnvelopeAtX(event.GetX());
+                  mEnvelopeEditors.push_back(
-            if (clickedEnvelope)
+                     std::make_unique< EnvelopeEditor >( *e2, true ) );
-               mEnvelopeEditorRight =
+               else {
-                  std::make_unique< EnvelopeEditor >( *clickedEnvelope, true );
+                   // There isn't necessarily an envelope there; no guarantee a
+                   // linked track has the same WaveClip structure...
+                }
+            }
          }
 
          return RefreshNone;
@@ -211,9 +216,9 @@ UIHandle::Result EnvelopeHandle::Click
          if (!mEnvelope)
             return Cancelled;
          GetTimeTrackData( *pProject, *tt, mdBRange, mLog, mLower, mUpper);
-         mEnvelopeEditor =
+         mEnvelopeEditors.push_back(
-            std::make_unique< EnvelopeEditor >( *mEnvelope, false );
+            std::make_unique< EnvelopeEditor >( *mEnvelope, false )
-         mEnvelopeEditorRight.reset();
+         );
 
          return RefreshNone;
       },
@@ -289,8 +294,7 @@ UIHandle::Result EnvelopeHandle::Release
       _("Envelope")
    );
 
-   mEnvelopeEditor.reset();
+   mEnvelopeEditors.clear();
-   mEnvelopeEditorRight.reset();
 
    using namespace RefreshCode;
    return needUpdate ? RefreshCell : RefreshNone;
@@ -299,8 +303,7 @@ UIHandle::Result EnvelopeHandle::Release
 UIHandle::Result EnvelopeHandle::Cancel(AudacityProject *pProject)
 {
    pProject->RollbackState();
-   mEnvelopeEditor.reset();
+   mEnvelopeEditors.clear();
-   mEnvelopeEditorRight.reset();
    return RefreshCode::RefreshCell;
 }
 
@@ -313,14 +316,13 @@ bool EnvelopeHandle::ForwardEventToEnvelopes
 
    // AS: I'm not sure why we can't let the Envelope take care of
    //  redrawing itself.  ?
-   bool needUpdate =
+   bool needUpdate = false;
-      mEnvelopeEditor->MouseEvent(
+   for (const auto &pEditor : mEnvelopeEditors) {
-         event, mRect, viewInfo, mLog, mdBRange, mLower, mUpper);
+      needUpdate =
-
+         pEditor->MouseEvent(
-   if (mEnvelopeEditorRight)
+            event, mRect, viewInfo, mLog, mdBRange, mLower, mUpper)
-      needUpdate |=
+         || needUpdate;
-         mEnvelopeEditorRight->MouseEvent(
+   }
-            event, mRect, viewInfo, mLog, mdBRange, mLower, mUpper);
 
    return needUpdate;
 }

src/tracks/ui/EnvelopeHandle.h

@@ -14,6 +14,8 @@ Paul Licameli split from TrackPanel.cpp
 #include "../../UIHandle.h"
 #include "../../MemoryX.h"
 
+#include <vector>
+
 class wxMouseEvent;
 class wxMouseState;
 #include <wx/gdicmn.h>
@@ -85,8 +87,7 @@ private:
    double mdBRange{};
 
    Envelope *mEnvelope{};
-   std::unique_ptr<EnvelopeEditor> mEnvelopeEditor;
+   std::vector< std::unique_ptr<EnvelopeEditor> > mEnvelopeEditors;
-   std::unique_ptr<EnvelopeEditor> mEnvelopeEditorRight;
 
    bool mTimeTrack{};
 };

src/tracks/ui/TimeShiftHandle.cpp

@@ -152,6 +152,21 @@ namespace
          AddClipsToCaptured( state, t, t->GetStartTime(), t->GetEndTime() );
    }
 
+   WaveTrack *NthChannel(WaveTrack &leader, int nn)
+   {
+      if (nn < 0)
+         return nullptr;
+      return *TrackList::Channels( &leader ).begin().advance(nn);
+   }
+
+   int ChannelPosition(const Track *pChannel)
+   {
+      return static_cast<int>(
+         TrackList::Channels( pChannel )
+            .EndingAfter( pChannel ).size()
+      ) - 1;
+   }
+
    // Don't count right channels.
    WaveTrack *NthAudioTrack(TrackList &list, int nn)
    {
@@ -206,16 +221,11 @@ namespace
                clip.track->Offset( offset );
          }
       }
-      else if ( pTrack ) {
+      else if ( pTrack )
          // Was a shift-click
-         for (auto channel =
+         for (auto channel : TrackList::Channels( pTrack ))
-                 pTrack->GetLink() && !pTrack->GetLinked()
-                    ? pTrack->GetLink() : pTrack;
-              channel;
-              channel = channel->GetLinked() ? channel->GetLink() : nullptr)
             channel->Offset( offset );
    }
-   }
 }
 
 void TimeShiftHandle::CreateListOfCapturedClips
@@ -236,16 +246,12 @@ void TimeShiftHandle::CreateListOfCapturedClips
       state.capturedClipArray.push_back
          (TrackClip( &capturedTrack, state.capturedClip ));
 
-      // Check for stereo partner
+      if (state.capturedClip) {
-      Track *partner = capturedTrack.GetLink();
+         // Check for other channels
-      WaveTrack *wt;
+         auto wt = static_cast<WaveTrack*>(&capturedTrack);
-      if (state.capturedClip &&
+         for ( auto channel : TrackList::Channels( wt ).Excluding( wt ) )
-            // Assume linked track is wave or null
+            if (WaveClip *const clip = FindClipAtTime(channel, clickTime))
-            nullptr != (wt = static_cast<WaveTrack*>(partner))) {
+               state.capturedClipArray.push_back(TrackClip(channel, clip));
-         WaveClip *const clip = FindClipAtTime(wt, clickTime);
-
-         if (clip)
-            state.capturedClipArray.push_back(TrackClip(partner, clip));
       }
    }
 
@@ -493,22 +499,28 @@ namespace {
       for ( auto &trackClip : state.capturedClipArray ) {
          if (trackClip.clip) {
             // Move all clips up or down by an equal count of audio tracks.
+            // Can only move between tracks with equal numbers of channels,
+            // and among corresponding channels.
+
             Track *const pSrcTrack = trackClip.track;
             auto pDstTrack = NthAudioTrack(trackList,
                diff + TrackPosition(trackList, pSrcTrack));
-            // Can only move mono to mono, or left to left, or right to right
+            if (!pDstTrack)
-            // And that must be so for each captured clip
-            bool stereo = (pSrcTrack->GetLink() != 0);
-            if (pDstTrack && stereo && !pSrcTrack->GetLinked())
-               // Assume linked track is wave or null
-               pDstTrack = static_cast<WaveTrack*>(pDstTrack->GetLink());
-            bool ok = pDstTrack &&
-            (stereo == (pDstTrack->GetLink() != 0)) &&
-            (!stereo || (pSrcTrack->GetLinked() == pDstTrack->GetLinked()));
-            if (ok)
-               trackClip.dstTrack = pDstTrack;
-            else
                return false;
+
+            if (TrackList::Channels(pSrcTrack).size() !=
+                TrackList::Channels(pDstTrack).size())
+               return false;
+
+            auto pDstChannel = NthChannel(
+               *pDstTrack, ChannelPosition(pSrcTrack));
+
+            if (!pDstChannel) {
+               wxASSERT(false);
+               return false;
+            }
+
+           trackClip.dstTrack = pDstChannel;
          }
       }
       return true;

src/tracks/ui/TrackButtonHandles.cpp

@@ -34,9 +34,9 @@ UIHandle::Result MinimizeButtonHandle::CommitChanges
    auto pTrack = mpTrack.lock();
    if (pTrack)
    {
-      pTrack->SetMinimized(!pTrack->GetMinimized());
+      bool wasMinimized = pTrack->GetMinimized();
-      if (pTrack->GetLink())
+      for (auto channel : TrackList::Channels(pTrack.get()))
-         pTrack->GetLink()->SetMinimized(pTrack->GetMinimized());
+         channel->SetMinimized(!wasMinimized);
       pProject->ModifyState(true);
 
       // Redraw all tracks when any one of them expands or contracts

src/tracks/ui/TrackControls.cpp

@@ -209,11 +209,8 @@ void TrackMenuTable::OnSetName(wxCommandEvent &)
       if (bResult) 
       {
          wxString newName = Command.mName;
-         pTrack->SetName(newName);
+         for (auto channel : TrackList::Channels(pTrack))
-         // if we have a linked channel this name should change as well
+            channel->SetName(newName);
-         // (otherwise sort by name and time will crash).
-         if (pTrack->GetLinked())
-            pTrack->GetLink()->SetName(newName);
 
          MixerBoard *const pMixerBoard = proj->GetMixerBoard();
          auto pt = dynamic_cast<PlayableTrack*>(pTrack);