Temporary session-format compatibility (revert before release)

Saving the new ControlList interpolation methods (enum) breaks loading
the session in older version. The session-format version will
need to be increased.

Until then:
 * Fader automation + region gain envelope uses linear fades
 * The automation-line visible in the GUI does not match the actual fade
   (the y-axis is log/exp-scale, the fade is linear)
 * Adding new points on the line is not using the correct initial value
 * Custom changes of interpolation mode are not available

Neither of these issues is a regression.

gtk2_ardour/automation_line.cc

@@ -1168,6 +1168,7 @@ AutomationLine::view_to_model_coord (double& x, double& y) const
 void
 AutomationLine::view_to_model_coord_y (double& y) const
 {
+#ifdef XXX_NEW_INTERPOLATON__BREAK_SESSION_FORMAT_XXX
 	if (alist->default_interpolation () != alist->interpolation()) {
 		switch (alist->interpolation()) {
 			case AutomationList::Linear:
@@ -1178,6 +1179,7 @@ AutomationLine::view_to_model_coord_y (double& y) const
 				break;
 		}
 	}
+#endif
 	y = _desc.from_interface (y);
 }
 
@@ -1202,6 +1204,7 @@ AutomationLine::apply_delta (double& val, double delta) const
 void
 AutomationLine::model_to_view_coord_y (double& y) const
 {
+#ifdef XXX_NEW_INTERPOLATON__BREAK_SESSION_FORMAT_XXX
 	if (alist->default_interpolation () != alist->interpolation()) {
 		switch (alist->interpolation()) {
 			case AutomationList::Linear:
@@ -1212,6 +1215,7 @@ AutomationLine::model_to_view_coord_y (double& y) const
 				break;
 		}
 	}
+#endif
 	y = _desc.to_interface (y);
 }
 

gtk2_ardour/automation_time_axis.cc

@@ -624,7 +624,7 @@ AutomationTimeAxisView::build_display_menu ()
 		items.push_back (MenuElem (_("Mode"), *auto_mode_menu));
 
 	} else {
-
+#ifdef XXX_NEW_INTERPOLATON__BREAK_SESSION_FORMAT_XXX
 		Menu* auto_mode_menu = manage (new Menu);
 		auto_mode_menu->set_name ("ArdourContextMenu");
 		MenuList& am_items = auto_mode_menu->items();
@@ -664,6 +664,7 @@ AutomationTimeAxisView::build_display_menu ()
 			delete auto_mode_menu;
 			auto_mode_menu = 0;
 		}
+#endif
 	}
 
 	/* make sure the automation menu state is correct */

libs/ardour/automation_list.cc

@@ -211,6 +211,10 @@ AutomationList::default_interpolation () const
 		case GainAutomation:
 		case BusSendLevel:
 		case EnvelopeAutomation:
+#ifndef XXX_NEW_INTERPOLATON__BREAK_SESSION_FORMAT_XXX
+			/* use old, wrong linear gain interpolation */
+			return ControlList::Linear;
+#endif
 			return ControlList::Exponential;
 			break;
 		case TrimAutomation:
@@ -342,7 +346,22 @@ AutomationList::state (bool full)
 
 	root->set_property ("automation-id", EventTypeMap::instance().to_symbol(_parameter));
 	root->set_property ("id", id());
+
+#ifndef XXX_NEW_INTERPOLATON__BREAK_SESSION_FORMAT_XXX
+	/* force new enums to existing ones in session-file */
+	Evoral::ControlList::InterpolationStyle is = _interpolation;
+	switch (is) {
+		case ControlList::Exponential:
+		case ControlList::Logarithmic:
+			is = ControlList::Linear;
+			break;
+		default:
+			break;
+	}
+	root->set_property ("interpolation-style", is);
+#else
 	root->set_property ("interpolation-style", _interpolation);
+#endif
 
 	if (full) {
 		/* never serialize state with Write enabled - too dangerous
@@ -512,6 +531,12 @@ AutomationList::set_state (const XMLNode& node, int version)
 	if (!node.get_property (X_("interpolation-style"), _interpolation)) {
 		_interpolation = default_interpolation ();
 	}
+#ifndef XXX_NEW_INTERPOLATON__BREAK_SESSION_FORMAT_XXX
+	/* internally force logarithmic and Trim params to use Log-scale */
+	if (_desc.logarithmic || _parameter.type() == TrimAutomation) {
+		_interpolation = ControlList::Logarithmic;
+	}
+#endif
 
 	if (node.get_property (X_("state"), _state)) {
 		if (_state == Write) {