automation drawing: thinning does not work well with snapped-drawn lines

Also, adding points to a ControlList can fail and that's OK

gtk2_ardour/automation_time_axis.cc

@@ -791,7 +791,7 @@ AutomationTimeAxisView::build_display_menu ()
 }
 
 void
-AutomationTimeAxisView::merge_drawn_line (DrawnPoints const & points)
+AutomationTimeAxisView::merge_drawn_line (DrawnPoints const & points, bool thin)
 {
 	if (points.empty()) {
 		return;
@@ -812,7 +812,6 @@ AutomationTimeAxisView::merge_drawn_line (DrawnPoints const & points)
 
 	XMLNode& before = list->get_state();
 	std::list<Selectable*> results;
-	bool failed = false;
 
 	Temporal::timepos_t earliest = points.front().when;
 	Temporal::timepos_t latest = points.back().when;
@@ -830,19 +829,13 @@ AutomationTimeAxisView::merge_drawn_line (DrawnPoints const & points)
 		/* map using line */
 		_line->view_to_model_coord_y (y);
 
-		if (!list->editor_add (dp.when, y, false)) {
-			failed = true;
-			break;
-		}
+		list->editor_add (dp.when, y, false);
 	}
 
-	if (failed) {
-		/* XXX do something */
-		return;
+	if (thin) {
+		list->thin (50.0);
 	}
 
-	list->thin (1.0);
-
 	if (_control->automation_state () == ARDOUR::Off) {
 		set_automation_state (ARDOUR::Play);
 	}

gtk2_ardour/automation_time_axis.h

@@ -154,7 +154,7 @@ public:
 	};
 
 	typedef std::vector<DrawnPoint> DrawnPoints;
-	void merge_drawn_line (DrawnPoints const &);
+	void merge_drawn_line (DrawnPoints const &, bool thin);
 
 protected:
 	/* Note that for MIDI controller "automation" (in regions), all of these

gtk2_ardour/editor_drag.cc

@@ -7248,6 +7248,7 @@ AutomationDrawDrag::AutomationDrawDrag (Editor* editor, ArdourCanvas::Rectangle&
 	, dragging_line (nullptr)
 	, direction (0)
 	, edge_x (0)
+	, did_snap (false)
 {
 	DEBUG_TRACE (DEBUG::Drags, "New AutomationDrawDrag\n");
 }
@@ -7282,6 +7283,11 @@ AutomationDrawDrag::motion (GdkEvent* ev, bool first_move)
 
 	timepos_t pos (_drags->current_pointer_time ());
 	_editor->snap_to_with_modifier (pos, ev);
+
+	if (pos != _drags->current_pointer_time()) {
+		did_snap = true;
+	}
+
 	double const pointer_x = _editor->time_to_pixel (pos);
 
 	ArdourCanvas::Rect r = base_rect.item_to_canvas (base_rect.get());
@@ -7346,11 +7352,13 @@ AutomationDrawDrag::finished (GdkEvent* event, bool motion_occured)
 		return;
 	}
 
-	atv->merge_drawn_line (drawn_points);
+	/* ControlList::thin() works very badly with the stair-cased lines that
+	   result from snapping.
+	*/
+	atv->merge_drawn_line (drawn_points, !did_snap);
 }
 
 void
 AutomationDrawDrag::aborted (bool)
 {
 }
-

gtk2_ardour/editor_drag.h

@@ -1597,6 +1597,7 @@ private:
 	int direction;
 	int edge_x;
 	AutomationTimeAxisView::DrawnPoints drawn_points;
+	bool did_snap;
 };
 
 #endif /* __gtk2_ardour_editor_drag_h_ */