Iterate over the pending tracks for drawing

src/Project.cpp

@@ -2019,25 +2019,6 @@ 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

@@ -192,8 +192,6 @@ 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; }
 

src/Track.cpp

@@ -1560,3 +1560,69 @@ std::shared_ptr<Track> TrackList::FindPendingChangedTrack(TrackId id) const
       return {};
    return *it;
 }
+
+// Make begin iterator
+PendingTrackIterator::PendingTrackIterator
+(TrackList *list, const std::shared_ptr<TrackListIterator> &pIter)
+   : mList{ list }
+   , mpIter{ pIter }
+{
+   auto &pending = mList->FindPendingNewTracks();
+
+   // Assume no invalidation of these iterators happens during the lifetime
+   // of this!
+   mpPendingIt = pending.begin(), mpPendingEnd = pending.end();
+
+   mpTrack = Track::Pointer( mpIter->First() );
+   SubstituteTrack();
+      
+   mDoingExtras = !mpTrack;
+   FindExtraTrack();
+}
+
+// Make end iterator; the only important thing is to define operators == and
+// != with other iterators
+PendingTrackIterator::PendingTrackIterator()
+   : mList{ nullptr }
+   , mpIter{ }
+{
+   mDoingExtras = true;
+}
+
+PendingTrackIterator &PendingTrackIterator::operator++()
+{
+   if (!mDoingExtras) {
+      Track *next = mpIter->Next();
+      if (next) {
+         mpTrack = Track::Pointer( next );
+         SubstituteTrack();
+      }
+      else
+         mDoingExtras = true;
+   }
+   FindExtraTrack();
+   return *this;
+}
+
+void PendingTrackIterator::SubstituteTrack()
+{
+   if (mpTrack) {
+      auto sub = mList->FindPendingChangedTrack( mpTrack->GetId() );
+      if (sub)
+         mpTrack = sub;
+   }
+}
+
+void PendingTrackIterator::FindExtraTrack()
+{
+   if (mDoingExtras) {
+      auto pCondIter = dynamic_cast<TrackListCondIterator*>(mpIter.get());
+      while(
+         mpTrack.reset(),
+         mpPendingIt != mpPendingEnd &&
+         (mpTrack = *mpPendingIt++,
+          pCondIter &&
+          !pCondIter->Condition(mpTrack.get())))
+      {}
+   }
+}

src/Track.h

@@ -501,7 +501,6 @@ class AUDACITY_DLL_API TrackListCondIterator /* not final */ : public TrackListI
       Track *Prev(bool skiplinked = false) override;
       Track *Last(bool skiplinked = false) override;
 
-   protected:
       // NEW virtual
       virtual bool Condition(Track *t) = 0;
 };
@@ -579,6 +578,52 @@ class AUDACITY_DLL_API SyncLockedTracksIterator final : public TrackListIterator
 };
 
 
+// Iterates over the tracks, substituting any pending replacement tracks
+// for the actual, and always appending the added tracks, but then
+// also filtering all tracks according to the criterion in the
+// TrackListIterator given to the constructor.
+// Iterator may be invalidated if the project's TrackList is mutated during
+// the iterator's lifetime (though not in case of RegisterPendingChangedTrack()).
+class PendingTrackIterator {
+public:
+   // Construct a begin iterator
+   PendingTrackIterator
+      (TrackList *list,
+       // Track iterator that can include a condition
+       const std::shared_ptr<TrackListIterator> &pIter);
+
+   // Construct an end iterator
+   PendingTrackIterator();
+
+   PendingTrackIterator &operator++();
+
+   const std::shared_ptr<Track> &operator* () const { return mpTrack; }
+
+   bool operator == (const PendingTrackIterator &other) const
+   // Test for identity of the tracks pointed to should be a sufficient
+   // test of iterator equality, assuming no track is ever duplicated in the
+   // sequence, which should be the case, and that an end iterator stores a
+   // null pointer.
+   { return mpTrack == other.mpTrack; }
+
+   bool operator != (const PendingTrackIterator &other) const
+   { return !(*this == other); }
+
+protected:
+
+   std::shared_ptr<Track> mpTrack;
+
+private:
+   void SubstituteTrack();
+   void FindExtraTrack();
+
+   TrackList *mList;
+   std::shared_ptr<TrackListIterator> mpIter;
+
+   bool mDoingExtras{ false };
+   ListOfTracks::const_iterator mpPendingIt, mpPendingEnd;
+};
+
 /** \brief TrackList is a flat linked list of tracks supporting Add,  Remove,
  * Clear, and Contains, plus serialization of the list of tracks.
  */

src/TrackArtist.cpp

@@ -339,8 +339,7 @@ void TrackArtist::SetMargins(int left, int top, int right, int bottom)
 }
 
 void TrackArtist::DrawTracks(TrackPanelDrawingContext &context,
-                             TrackList * tracks,
-                             Track * start,
+                             const std::function< Range() > &range,
                              const wxRegion & reg,
                              const wxRect & rect,
                              const wxRect & clip,
@@ -352,11 +351,10 @@ void TrackArtist::DrawTracks(TrackPanelDrawingContext &context,
 {
    wxRect trackRect = rect;
    wxRect stereoTrackRect;
-   TrackListIterator iter(tracks);
-   Track *t;
 
    bool hasSolo = false;
-   for (t = iter.First(); t; t = iter.Next()) {
+   for (auto &track : range()) {
+      auto t = track.get();
       auto pt = dynamic_cast<const PlayableTrack *>(t);
       if (pt && pt->GetSolo()) {
          hasSolo = true;
@@ -379,8 +377,8 @@ void TrackArtist::DrawTracks(TrackPanelDrawingContext &context,
 
    gPrefs->Read(wxT("/GUI/ShowTrackNameInWaveform"), &mbShowTrackNameInWaveform, false);
 
-   t = iter.StartWith(start);
-   while (t) {
+   for (auto &track : range()) {
+      auto t = track.get();
       trackRect.y = t->GetY() - zoomInfo.vpos;
       trackRect.height = t->GetHeight();
 
@@ -430,8 +428,6 @@ void TrackArtist::DrawTracks(TrackPanelDrawingContext &context,
                    selectedRegion, zoomInfo,
                    drawEnvelope, bigPoints, drawSliders, hasSolo);
       }
-
-      t = iter.Next();
    }
 }
 

src/TrackArtist.h

@@ -24,6 +24,8 @@
 #include "Experimental.h"
 #include "audacity/Types.h"
 
+#include <functional>
+
 class wxDC;
 class wxRect;
 class wxHashTable;
@@ -36,10 +38,10 @@ class WaveClip;
 class NoteTrack;
 class LabelTrack;
 class TimeTrack;
-class TrackList;
 class Ruler;
 class SelectedRegion;
 class ZoomInfo;
+class PendingTrackIterator;
 
 struct TrackPanelDrawingContext;
 
@@ -54,8 +56,10 @@ class AUDACITY_DLL_API TrackArtist {
    ~TrackArtist();
 
    void SetColours(int iColorIndex);
+
+   using Range = IteratorRange< PendingTrackIterator >;
    void DrawTracks(TrackPanelDrawingContext &context,
-                   TrackList *tracks, Track *start,
+                   const std::function< Range() > &range,
                    const wxRegion & reg,
                    const wxRect & rect, const wxRect & clip,
                    const SelectedRegion &selectedRegion, const ZoomInfo &zoomInfo,

src/TrackPanel.cpp

@@ -1846,8 +1846,17 @@ 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(), first.get(),
+   auto project = GetProject();
+   // Make a function that reproduces the range, because, quirkily, the range
+   // can't be copied and iterated twice.  Fix that later.
+   auto range = [&]{
+      return make_iterator_range(
+         PendingTrackIterator{ project->GetTracks(),
+             std::make_shared<VisibleTrackIterator>( project ) },
+         PendingTrackIterator{}
+      );
+   };
+   mTrackArtist->DrawTracks(context, range,
                             region, tracksRect, clip,
                             mViewInfo->selectedRegion, *mViewInfo,
                             envelopeFlag, bigPointsFlag, sliderFlag);
@@ -1869,8 +1878,13 @@ void TrackPanel::DrawEverythingElse(TrackPanelDrawingContext &context,
    wxRect trackRect = clip;
    trackRect.height = 0;   // for drawing background in no tracks case.
 
-   VisibleTrackIterator iter(GetProject());
-   for (Track *t = iter.First(); t; t = iter.Next()) {
+   auto project = GetProject();
+   PendingTrackIterator
+      begin{ project->GetTracks(),
+             std::make_shared<VisibleTrackIterator>( project ) },
+      end;
+   for (const auto &track : make_iterator_range(begin, end)) {
+      auto t = track.get();
       trackRect.y = t->GetY() - mViewInfo->vpos;
       trackRect.height = t->GetHeight();