Bug 1484 - Cannot one-step extend/contract selections vertically or horizontally to specific TrackSelFunc

Progresses us a little towards closing.  Ctrl-Click on waveform now removes track selection status, not just adds it, and we don't flicker on again subsequently when we drag.  Ctrl-Click won't remove the last remaining selection (by design).  Shift-Click can now reduce us down to one track, rather than the previous behaviour when reducing track selection.

src/TrackPanel.cpp

@@ -1871,6 +1871,16 @@ void TrackPanel::SelectTrack(Track *pTrack, bool selected, bool updateLastPicked
    }
 }
 
+size_t TrackPanel::GetSelectedTrackCount(){
+   size_t count = 0;
+
+   TrackListIterator iter(GetTracks());
+   for (Track *t = iter.First(); t; t = iter.Next()) {
+      count +=  t->GetSelected() ? 1:0;
+   }
+   return count;
+}
+
 void TrackPanel::SelectRangeOfTracks(Track *sTrack, Track *eTrack)
 {
    if (eTrack) {
@@ -1907,18 +1917,18 @@ void TrackPanel::ChangeSelectionOnShiftClick(Track * pTrack){
    TrackListIterator iter(GetTracks());
    for (Track *t = iter.First(); t; t = iter.Next()) {
       const bool isSelected = t->GetSelected();
-      // If our track is after the first, extend from the first.
-      if( t == pTrack ){
-         pExtendFrom = pFirst;
-      }
       // Record first and last selected.
       if( isSelected ){
          if( !pFirst )
             pFirst = t;
          pLast = t;
       }
+      // If our track is at or after the first, extend from the first.
+      if( t == pTrack ){
+         pExtendFrom = pFirst;
       }
-   // Our track was the first or earlier.  Extend from the last.
+   }
+   // Our track was earlier than the first.  Extend from the last.
    if( !pExtendFrom )
       pExtendFrom = pLast;
 
@@ -1976,10 +1986,12 @@ void TrackPanel::SelectionHandleClick(wxMouseEvent & event,
       if( bShiftDown )
          ChangeSelectionOnShiftClick( pTrack );
       if( bCtrlDown ){
-         //bool bIsSelected = pTrack->GetSelected();
-         bool bIsSelected = false;
+         bool bIsSelected = pTrack->GetSelected();
+         //bool bIsSelected = true;
          // could set bIsSelected true here, but toggling is more technically correct.
          // if we want to match behaviour in Track Control Panel.
+         // Don't toggle away the last selected track.
+         if( !bIsSelected || GetSelectedTrackCount() > 1 )
             SelectTrack( pTrack, !bIsSelected, false );
       }
 
@@ -2821,6 +2833,7 @@ void TrackPanel::SelectionHandleDrag(wxMouseEvent & event, Track *clickedTrack)
    // Handle which tracks are selected
    Track *sTrack = pTrack;
    Track *eTrack = FindTrack(x, y, false, false, NULL);
+   if( !event.ControlDown() )
       SelectRangeOfTracks(sTrack, eTrack);
 
 #ifdef USE_MIDI

src/TrackPanel.h

@@ -291,6 +291,7 @@ class AUDACITY_DLL_API TrackPanel final : public OverlayPanel {
    // AS: Selection handling
    void SelectTrack(Track *track, bool selected, bool updateLastPicked = true);
    void SelectRangeOfTracks(Track *sTrack, Track *eTrack);
+   size_t GetSelectedTrackCount();
    virtual void HandleSelect(wxMouseEvent & event);
    virtual void SelectionHandleDrag(wxMouseEvent &event, Track *pTrack);