fix another #warning from the pianorule refactoring

There is one single place in AutomationLine code where we need to callback
to its AutomationTimeAxisView, if it is part of one, regarding automation
state. This permits that to happen

gtk2_ardour/automation_line.cc

@@ -112,6 +112,7 @@ AutomationLine::AutomationLine (const string&                   name,
 	, _desc (desc)
 	, _control_points_inherit_color (true)
 	, _sensitive (true)
+	, atv (nullptr)
 {
 	group = new ArdourCanvas::Container (&parent, ArdourCanvas::Duple(0, 1.5));
 	CANVAS_DEBUG_NAME (group, "automation line group");
@@ -1628,8 +1629,9 @@ AutomationLine::add (std::shared_ptr<AutomationControl> control, GdkEvent* event
 	if (alist->editor_add (when, y, with_guard_points)) {
 
 		if (control->automation_state () == ARDOUR::Off) {
-#warning paul make this work again .. call back to ATV or similar
-			// set_automation_state (ARDOUR::Play);
+			if (atv) {
+				atv->set_automation_state (ARDOUR::Play);
+			}
 		}
 
 		if (UIConfiguration::instance().get_automation_edit_cancels_auto_hide () && control == session->recently_touched_controllable ()) {
@@ -1647,3 +1649,9 @@ AutomationLine::add (std::shared_ptr<AutomationControl> control, GdkEvent* event
 		session->set_dirty ();
 	}
 }
+
+void
+AutomationLine::set_atv (AutomationTimeAxisView& a)
+{
+	atv = &a;
+}

gtk2_ardour/automation_line.h

@@ -78,6 +78,9 @@ public:
 
 	virtual ~AutomationLine ();
 
+
+	void set_atv (AutomationTimeAxisView&);
+
 	virtual Temporal::timepos_t get_origin () const;
 
 	ArdourCanvas::Rectangle* drag_base() const { return _drag_base; }
@@ -271,6 +274,7 @@ private:
 	const ARDOUR::ParameterDescriptor _desc;
 	bool _control_points_inherit_color;
 	bool _sensitive;
+	AutomationTimeAxisView* atv;
 
 	friend class AudioRegionGainLine;
 	friend class RegionFxLine;

gtk2_ardour/editor_automation_line.cc

@@ -34,15 +34,21 @@ using namespace ARDOUR;
 /** @param converter A TimeConverter whose origin_b is the start time of the AutomationList in session samples.
  *  This will not be deleted by EditorAutomationLine.
  */
-EditorAutomationLine::EditorAutomationLine (const string&                              name,
-                                TimeAxisView&                              tv,
-                                ArdourCanvas::Item&                        parent,
-                                std::shared_ptr<AutomationList>            al,
-                                const ParameterDescriptor&                 desc)
+EditorAutomationLine::EditorAutomationLine (const string&                   name,
+                                            TimeAxisView&                   tv,
+                                            ArdourCanvas::Item&             parent,
+                                            std::shared_ptr<AutomationList> al,
+                                            const ParameterDescriptor&      desc)
 	: AutomationLine (name, tv.editor(), parent, nullptr, al, desc)
 	, trackview (tv)
 {
 	line->set_data ("trackview", &trackview);
+
+	AutomationTimeAxisView* atv = dynamic_cast<AutomationTimeAxisView*> (&tv);
+
+	if (atv) {
+		set_atv (*atv);
+	}
 }
 
 EditorAutomationLine::~EditorAutomationLine ()

gtk2_ardour/editor_automation_line.h

@@ -63,11 +63,11 @@ class PublicEditor;
 class EditorAutomationLine : public AutomationLine
 {
 public:
-	EditorAutomationLine (const std::string&                name,
-	                TimeAxisView&                           tv,
-	                ArdourCanvas::Item&                     parent,
-	                std::shared_ptr<ARDOUR::AutomationList> al,
-	                const ARDOUR::ParameterDescriptor&      desc);
+	EditorAutomationLine (const std::string&                      name,
+	                      TimeAxisView&                           tv,
+	                      ArdourCanvas::Item&                     parent,
+	                      std::shared_ptr<ARDOUR::AutomationList> al,
+	                      const ARDOUR::ParameterDescriptor&      desc);
 
 
 	virtual ~EditorAutomationLine ();

gtk2_ardour/midi_automation_line.cc

@@ -32,12 +32,12 @@
 using namespace std;
 
 MidiAutomationLine::MidiAutomationLine (
-	const std::string&                                      name,
-	TimeAxisView&                                           tav,
-	ArdourCanvas::Item&                                     parent,
-	std::shared_ptr<ARDOUR::AutomationList>               list,
-	std::shared_ptr<ARDOUR::MidiRegion>                   region,
-	Evoral::Parameter                                       parameter)
+	const std::string&                      name,
+	TimeAxisView&                           tav,
+	ArdourCanvas::Item&                     parent,
+	std::shared_ptr<ARDOUR::AutomationList> list,
+	std::shared_ptr<ARDOUR::MidiRegion>     region,
+	Evoral::Parameter                       parameter)
 	: EditorAutomationLine (name, tav, parent, list, parameter)
 	, _region (region)
 	, _parameter (parameter)