Add option to zoom using button press in the time rulers and dragging vertically

This is a common operation used for zooming in other DAWs like Ableton Live and
Cubase. To support such a usage pattern without changing the existing behaviour
of the ruler area I've made it an option that is false by default.

The behaviour of RulerDragZoom is intentionally different than a CursorDrag
that occurs in the rest of the ruler area in that it doesn't follow the snap to
grid setting and no locate related stuff occurs until button release.

There are some issues with responsiveness with more than a few hundred regions
or a large amount of MIDI events/notes.

Implements feature #6768

gtk2_ardour/editor.h

@@ -2272,6 +2272,7 @@ class Editor : public PublicEditor, public PBD::ScopedConnectionList, public ARD
 	friend class ControlPointDrag;
 	friend class LineDrag;
 	friend class RubberbandSelectDrag;
+	friend class RulerZoomDrag;
 	friend class EditorRubberbandSelectDrag;
 	friend class TimeFXDrag;
 	friend class ScrubDrag;

gtk2_ardour/editor_canvas_events.cc

@@ -1078,6 +1078,18 @@ Editor::canvas_ruler_event (GdkEvent *event, ArdourCanvas::Item* item, ItemType
 		return handled;
 	}
 
+	switch (event->type) {
+	case GDK_BUTTON_PRESS:
+		if (UIConfiguration::instance ().get_use_time_rulers_to_zoom_with_vertical_drag () &&
+		    Keyboard::no_modifier_keys_pressed (&event->button) && event->button.button == 1) {
+			_drags->set(new RulerZoomDrag(this, item), event);
+			return true;
+		}
+		break;
+	default:
+		break;
+	}
+
 	return typed_event (item, event, type);
 }
 

gtk2_ardour/editor_drag.cc

@@ -6447,3 +6447,56 @@ void
 RegionCutDrag::aborted (bool)
 {
 }
+
+RulerZoomDrag::RulerZoomDrag (Editor* e, ArdourCanvas::Item* item)
+	: Drag (e, item, true)
+{
+}
+
+void
+RulerZoomDrag::start_grab (GdkEvent* event, Gdk::Cursor* c)
+{
+	Drag::start_grab (event, c);
+
+	framepos_t where = _editor->canvas_event_sample(event);
+
+	_editor->_dragging_playhead = true;
+
+	_editor->playhead_cursor->set_position (where);
+}
+
+void
+RulerZoomDrag::motion (GdkEvent* event, bool)
+{
+	framepos_t where = _editor->canvas_event_sample(event);
+
+	_editor->playhead_cursor->set_position (where);
+
+	const double movement_limit = 20.0;
+	const double scale = 1.08;
+	const double y_delta = last_pointer_y() - current_pointer_y();
+
+	if (y_delta > 0 && y_delta < movement_limit) {
+		_editor->temporal_zoom_step_mouse_focus_scale (true, scale);
+	} else if (y_delta < 0 && y_delta > -movement_limit) {
+		_editor->temporal_zoom_step_mouse_focus_scale (false, scale);
+	}
+}
+
+void
+RulerZoomDrag::finished (GdkEvent*, bool)
+{
+	_editor->_dragging_playhead = false;
+
+	Session* s = _editor->session ();
+	if (s) {
+		s->request_locate (_editor->playhead_cursor->current_frame (), _was_rolling);
+		_editor->_pending_locate_request = true;
+	}
+
+}
+
+void
+RulerZoomDrag::aborted (bool)
+{
+}

gtk2_ardour/editor_drag.h

@@ -1189,5 +1189,21 @@ class CrossfadeEdgeDrag : public Drag
 	bool start;
 };
 
+class RulerZoomDrag : public Drag
+{
+public:
+	RulerZoomDrag (Editor*, ArdourCanvas::Item*);
+
+	void start_grab (GdkEvent*, Gdk::Cursor* c = 0);
+	void motion (GdkEvent *, bool);
+	void finished (GdkEvent*, bool);
+	void aborted (bool);
+
+	virtual bool allow_vertical_autoscroll () const {
+		return false;
+	}
+
+};
+
 #endif /* __gtk2_ardour_editor_drag_h_ */
 

gtk2_ardour/rc_option_editor.cc

@@ -2536,6 +2536,14 @@ if (!Profile->get_mixbus()) {
 			    ));
 }  // !mixbus
 
+	add_option (_("Editor"),
+		    new BoolOption (
+			    "use-time-rulers-to-zoom-with-vertical-drag",
+			    _("Use time rulers area to zoom when clicking and dragging vertically"),
+			    sigc::mem_fun (UIConfiguration::instance(), &UIConfiguration::get_use_time_rulers_to_zoom_with_vertical_drag),
+			    sigc::mem_fun (UIConfiguration::instance(), &UIConfiguration::set_use_time_rulers_to_zoom_with_vertical_drag)
+			    ));
+
 	add_option (_("Editor"),
 		    new BoolOption (
 			    "update-editor-during-summary-drag",

gtk2_ardour/ui_config_vars.h

@@ -49,6 +49,7 @@ UI_CONFIG_VARIABLE (bool, sound_midi_notes, "sound-midi-notes", false)
 UI_CONFIG_VARIABLE (bool, show_plugin_scan_window, "show-plugin-scan-window", false)
 UI_CONFIG_VARIABLE (bool, show_zoom_tools, "show-zoom-tools", true)
 UI_CONFIG_VARIABLE (bool, use_mouse_position_as_zoom_focus_on_scroll, "use-mouse-position-as-zoom-focus-on-scroll", true)
+UI_CONFIG_VARIABLE (bool, use_time_rulers_to_zoom_with_vertical_drag, "use-time-rulers-to-zoom-with-vertical-drag", false)
 UI_CONFIG_VARIABLE (bool, widget_prelight, "widget-prelight", true)
 UI_CONFIG_VARIABLE (bool, use_tooltips, "use-tooltips", true)
 UI_CONFIG_VARIABLE (std::string, mixer_strip_visibility, "mixer-element-visibility", "Input,PhaseInvert,RecMon,SoloIsoLock,Output,Comments")