Rewrite iteration over visible tracks in TrackArtist...

... also eliminating AudacityProject::GetFirstVisible.

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)

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);