Fix crashes in repainting, and update first visible track correctly

src/Project.cpp

@@ -944,8 +944,16 @@ AudacityProject::AudacityProject(wxWindow * parent, wxWindowID id,
    mLastSavedTracks = NULL;
 
    // Register for tracklist updates
+   mTracks->Connect(EVT_TRACKLIST_PERMUTED,
+                    wxCommandEventHandler(AudacityProject::OnTrackListUpdate),
+                    NULL,
+                    this);
    mTracks->Connect(EVT_TRACKLIST_DELETION,
-                    wxCommandEventHandler(AudacityProject::OnTrackListDeletion),
+                    wxCommandEventHandler(AudacityProject::OnTrackListUpdate),
+                    NULL,
+                    this);
+   mTracks->Connect(EVT_TRACKLIST_RESIZING,
+                    wxCommandEventHandler(AudacityProject::OnTrackListUpdate),
                     NULL,
                     this);
 
@@ -1974,9 +1982,8 @@ void AudacityProject::FixScrollbars()
       rescroll = false;
    }
 
-   if (lastv != mViewInfo.vpos) {
-      UpdateFirstVisible();
-   }
+   if (lastv != mViewInfo.vpos)
+      InvalidateFirstVisible();
 
    // wxScrollbar only supports int values but we need a greater range, so
    // we scale the scrollbar coordinates on demand. We only do this if we
@@ -2020,51 +2027,30 @@ void AudacityProject::FixScrollbars()
    }
 }
 
-Track *AudacityProject::GetFirstVisible()
+std::shared_ptr<Track> AudacityProject::GetFirstVisible()
 {
-   if (!mViewInfo.track && GetTracks()) {
+   auto pTrack = mViewInfo.track.lock();
+   if (!pTrack && GetTracks()) {
+      // Recompute on demand and memo-ize
       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
-            mViewInfo.track = t;
+            pTrack = Track::Pointer(t);
             break;
          }
       }
+      mViewInfo.track = pTrack;
    }
 
-   return mViewInfo.track;
+   return pTrack;
 }
 
-void AudacityProject::UpdateFirstVisible()
+void AudacityProject::InvalidateFirstVisible()
 {
-   if (!mViewInfo.track || !GetTracks()) {
-      return;
-   }
-
-   Track *t = mViewInfo.track;
-   mViewInfo.track = NULL;
-
-   if (t->GetY() >= mViewInfo.vpos) {
-      while (t && t->GetY() >= mViewInfo.vpos) {
-         t = mTracks->GetPrev(t);
-      }
-   }
-
-   while (t) {
-      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
-         mViewInfo.track = t;
-         return;
-      }
-      t = mTracks->GetNext(t);
-   }
-
-   return;
+   mViewInfo.track.reset();
 }
 
 void AudacityProject::UpdateLayout()
@@ -2222,9 +2208,9 @@ void AudacityProject::OnToolBarUpdate(wxCommandEvent & event)
 }
 
 // The projects tracklist has been updated
-void AudacityProject::OnTrackListDeletion(wxCommandEvent & event)
+void AudacityProject::OnTrackListUpdate(wxCommandEvent & event)
 {
-   mViewInfo.track = NULL;
+   InvalidateFirstVisible();
 
    event.Skip();
 }
@@ -2275,9 +2261,8 @@ void AudacityProject::DoScroll()
    int lastv = mViewInfo.vpos;
    mViewInfo.vpos = mVsbar->GetThumbPosition() * mViewInfo.scrollStep;
 
-   if (lastv != mViewInfo.vpos) {
-      UpdateFirstVisible();
-   }
+   if (lastv != mViewInfo.vpos)
+      InvalidateFirstVisible();
 
    //mchinen: do not always set this project to be the active one.
    //a project may autoscroll while playing in the background
@@ -2692,8 +2677,16 @@ void AudacityProject::OnCloseWindow(wxCloseEvent & event)
    mImportXMLTagHandler.reset();
 
    // Unregister for tracklist updates
+   mTracks->Disconnect(EVT_TRACKLIST_PERMUTED,
+                       wxCommandEventHandler(AudacityProject::OnTrackListUpdate),
+                       NULL,
+                       this);
    mTracks->Disconnect(EVT_TRACKLIST_DELETION,
-                       wxCommandEventHandler(AudacityProject::OnTrackListDeletion),
+                       wxCommandEventHandler(AudacityProject::OnTrackListUpdate),
+                       NULL,
+                       this);
+   mTracks->Disconnect(EVT_TRACKLIST_RESIZING,
+                       wxCommandEventHandler(AudacityProject::OnTrackListUpdate),
                        NULL,
                        this);
 
@@ -3529,7 +3522,7 @@ bool AudacityProject::HandleXMLTag(const wxChar *tag, const wxChar **attrs)
 
    if (longVpos != 0) {
       // PRL: It seems this must happen after SetSnapTo
-       mViewInfo.track = NULL;
+       mViewInfo.track.reset();
        mViewInfo.vpos = longVpos;
        mbInitializingScrollbar = true;
    }

src/Project.h

@@ -191,8 +191,8 @@ class AUDACITY_DLL_API AudacityProject final : public wxFrame,
    const ViewInfo &GetViewInfo() const { return mViewInfo; }
    ViewInfo &GetViewInfo() { return mViewInfo; }
 
-   Track *GetFirstVisible();
-   void UpdateFirstVisible();
+   std::shared_ptr<Track> GetFirstVisible();
+   void InvalidateFirstVisible();
 
    void GetPlayRegion(double* playRegionStart, double *playRegionEnd);
    bool IsPlayRegionLocked() { return mLockPlayRegion; }
@@ -355,7 +355,7 @@ public:
    void OnOpenAudioFile(wxCommandEvent & event);
    void OnODTaskUpdate(wxCommandEvent & event);
    void OnODTaskComplete(wxCommandEvent & event);
-   void OnTrackListDeletion(wxCommandEvent & event);
+   void OnTrackListUpdate(wxCommandEvent & event);
 
    void HandleResize();
    void UpdateLayout();

src/Track.cpp

@@ -741,6 +741,7 @@ Track *SyncLockedTracksIterator::Last(bool skiplinked)
 // is managing.  Any other classes that may be interested in get these updates
 // should use TrackList::Connect() and TrackList::Disconnect().
 //
+DEFINE_EVENT_TYPE(EVT_TRACKLIST_PERMUTED);
 DEFINE_EVENT_TYPE(EVT_TRACKLIST_RESIZING);
 DEFINE_EVENT_TYPE(EVT_TRACKLIST_DELETION);
 
@@ -856,6 +857,13 @@ void TrackList::RecalcPositions(TrackNodePointer node)
 #endif // EXPERIMENTAL_OUTPUT_DISPLAY
 }
 
+void TrackList::PermutationEvent()
+{
+   auto e = std::make_unique<wxCommandEvent>(EVT_TRACKLIST_PERMUTED);
+   // wxWidgets will own the event object
+   QueueEvent(e.release());
+}
+
 void TrackList::DeletionEvent()
 {
    auto e = std::make_unique<wxCommandEvent>(EVT_TRACKLIST_DELETION);
@@ -882,6 +890,7 @@ void TrackList::Permute(const std::vector<TrackNodePointer> &permutation)
    }
    auto n = begin();
    RecalcPositions(n);
+   PermutationEvent();
 }
 
 template<typename TrackKind>
@@ -1152,6 +1161,7 @@ void TrackList::SwapNodes(TrackNodePointer s1, TrackNodePointer s2)
 
    // Now correct the Index in the tracks, and other things
    RecalcPositions(s1);
+   PermutationEvent();
 }
 
 bool TrackList::MoveUp(Track * t)

src/Track.h

@@ -483,6 +483,9 @@ class AUDACITY_DLL_API SyncLockedTracksIterator final : public TrackListIterator
  * Clear, and Contains, plus serialization of the list of tracks.
  */
 
+// Posted when tracks are reordered but otherwise unchanged.
+DECLARE_EXPORTED_EVENT_TYPE(AUDACITY_DLL_API, EVT_TRACKLIST_PERMUTED, -1);
+
 // Posted when some track was added or changed its height.
 // The wxCommandEvent::GetClientData() method can be used to retrieve it.
 DECLARE_EXPORTED_EVENT_TYPE(AUDACITY_DLL_API, EVT_TRACKLIST_RESIZING, -1);
@@ -607,6 +610,7 @@ private:
    void DoAssign(const TrackList &that);
        
    void RecalcPositions(TrackNodePointer node);
+   void PermutationEvent();
    void DeletionEvent();
    void ResizingEvent(TrackNodePointer node);
 

src/TrackPanel.cpp

@@ -1636,7 +1636,8 @@ void TrackPanel::DrawTracks(wxDC * dc)
    bool sliderFlag     = bMultiToolDown;
 
    // The track artist actually draws the stuff inside each track
-   mTrackArtist->DrawTracks(GetTracks(), GetProject()->GetFirstVisible(),
+   auto first = GetProject()->GetFirstVisible();
+   mTrackArtist->DrawTracks(GetTracks(), first.get(),
                             *dc, region, tracksRect, clip,
                             mViewInfo->selectedRegion, *mViewInfo,
                             envelopeFlag, bigPointsFlag, sliderFlag);

src/ViewInfo.cpp

@@ -130,7 +130,6 @@ void ZoomInfo::FindIntervals
 ViewInfo::ViewInfo(double start, double screenDuration, double pixelsPerSecond)
    : ZoomInfo(start, pixelsPerSecond)
    , selectedRegion()
-   , track(NULL)
    , total(screenDuration)
    , sbarH(0)
    , sbarScreen(1)

src/ViewInfo.h

@@ -14,6 +14,7 @@
 #include <vector>
 #include <wx/event.h>
 #include "SelectedRegion.h"
+#include "MemoryX.h"
 
 
 class Track;
@@ -157,7 +158,7 @@ public:
 
    // Scroll info
 
-   Track *track;                // first visible track
+   std::weak_ptr<Track> track;                // first visible track
 
    double total;                // total width in secs
    // Current horizontal scroll bar positions, in pixels