Adding affordances to TrackPanel and TrackView

src/TrackPanel.cpp

@@ -1270,7 +1270,61 @@ struct VRulersAndChannels final : TrackPanelGroup {
    wxCoord mLeftOffset;
 };
 
-// n channels with vertical rulers, alternating with n - 1 resizers;
+//Simply fills area using specified brush and outlines borders
+class EmptyPanelRect final : public CommonTrackPanelCell
+{
+   int mFillBrushName;
+public:
+   explicit EmptyPanelRect(int fillBrushName)
+      : mFillBrushName(fillBrushName)
+   {
+   }
+
+   ~EmptyPanelRect() { }
+
+   void Draw(TrackPanelDrawingContext& context, const wxRect& rect, unsigned iPass)
+   {
+      if (iPass == TrackArtist::PassBackground)
+      {
+         context.dc.SetPen(*wxTRANSPARENT_PEN);
+         AColor::UseThemeColour(&context.dc, mFillBrushName);
+         context.dc.DrawRectangle(rect);
+         wxRect bevel(rect.x, rect.y, rect.width - 1, rect.height - 1);
+         AColor::BevelTrackInfo(context.dc, true, bevel, false);
+      }
+   }
+
+   std::shared_ptr<Track> DoFindTrack() override
+   {
+       return {};
+   }
+
+   std::vector<UIHandlePtr> HitTest(const TrackPanelMouseState& state, const AudacityProject* pProject)
+   {
+      return {};
+   }
+};
+
+//Simply place children one after another horizontally, without any specific logic
+struct HorizontalGroup final : TrackPanelGroup {
+
+   Refinement mRefinement;
+
+   HorizontalGroup(Refinement refinement) 
+      : mRefinement(std::move(refinement)) 
+   { 
+   }
+
+   Subdivision Children(const wxRect& /*rect*/) override
+   {
+      return { Axis::X, mRefinement };
+   }
+
+};
+
+
+// optional affordance area, and n channels with vertical rulers,
+// alternating with n - 1 resizers;
 // each channel-ruler pair might be divided into multiple views
 struct ChannelGroup final : TrackPanelGroup {
    ChannelGroup( const std::shared_ptr< Track > &pTrack, wxCoord leftOffset )
@@ -1283,8 +1337,19 @@ struct ChannelGroup final : TrackPanelGroup {
       const auto channels = TrackList::Channels( mpTrack.get() );
       const auto pLast = *channels.rbegin();
       wxCoord yy = rect.GetTop();
-      for ( auto channel : channels ) {
+      for ( auto channel : channels ) 
+      {
          auto &view = TrackView::Get( *channel );
+         if (auto affordance = view.GetAffordanceControls())
+         {
+            Refinement hgroup {
+               std::make_pair(rect.GetLeft() + 1, std::make_shared<EmptyPanelRect>(channel->GetSelected() ? clrTrackInfoSelected : clrTrackInfo)),
+               std::make_pair(mLeftOffset, affordance)
+            };
+            refinement.emplace_back(yy, std::make_shared<HorizontalGroup>(hgroup));
+            yy += kAffordancesAreaHeight;
+         }
+
          auto height = view.GetHeight();
          rect.SetTop( yy );
          rect.SetHeight( height - kSeparatorThickness );
@@ -1444,6 +1509,9 @@ struct Subgroup final : TrackPanelGroup {
          for ( auto channel : TrackList::Channels( leader ) ) {
             auto &view = TrackView::Get( *channel );
             height += view.GetHeight();
+
+            if (view.GetAffordanceControls())
+               height += kAffordancesAreaHeight;
          }
          refinement.emplace_back( yy,
             std::make_shared< ResizingChannelGroup >(

src/tracks/ui/TrackView.cpp

@@ -141,6 +141,13 @@ std::shared_ptr<const TrackVRulerControls> TrackView::GetVRulerControls() const
    return const_cast< TrackView* >( this )->GetVRulerControls();
 }
 
+std::shared_ptr<CommonTrackCell> TrackView::GetAffordanceControls()
+{
+   if (!mpAffordanceCellControl)
+      mpAffordanceCellControl = DoGetAffordanceControls();
+   return mpAffordanceCellControl;
+}
+
 void TrackView::DoSetY(int y)
 {
    mY = y;
@@ -165,6 +172,11 @@ void TrackView::DoSetHeight(int h)
    mHeight = h;
 }
 
+std::shared_ptr<CommonTrackCell> TrackView::DoGetAffordanceControls()
+{
+   return {};
+}
+
 namespace {
 
 // Attach an object to each project.  It receives track list events and updates

src/tracks/ui/TrackView.h

@@ -62,6 +62,9 @@ public:
    std::shared_ptr<TrackVRulerControls> GetVRulerControls();
    std::shared_ptr<const TrackVRulerControls> GetVRulerControls() const;
 
+   // by default returns nullptr, meaning that track has no drag controls area
+   std::shared_ptr<CommonTrackCell> GetAffordanceControls();
+
 
    void WriteXMLAttributes( XMLWriter & ) const override;
    bool HandleXMLAttribute( const wxChar *attr, const wxChar *value ) override;
@@ -88,8 +91,11 @@ protected:
    // Private factory to make appropriate object; class TrackView handles
    // memory management thereafter
    virtual std::shared_ptr<TrackVRulerControls> DoGetVRulerControls() = 0;
+   // May return nullptr (which is default) if track does not need affordance area
+   virtual std::shared_ptr<CommonTrackCell> DoGetAffordanceControls();
 
    std::shared_ptr<TrackVRulerControls> mpVRulerControls;
+   std::shared_ptr<CommonTrackCell> mpAffordanceCellControl;
 
 private:
    bool           mMinimized{ false };