taskbar: implement drag-and-drop task reordering

include/modules/wlr/taskbar.hpp

@@ -74,6 +74,10 @@ class Task {
   std::string app_id_;
   uint32_t state_ = 0;
 
+  int32_t drag_start_x;
+  int32_t drag_start_y;
+  int32_t drag_start_button = -1;
+
  private:
   std::string repr() const;
   std::string state_string(bool = false) const;
@@ -105,6 +109,11 @@ class Task {
 
   /* Callbacks for Gtk events */
   bool handle_clicked(GdkEventButton *);
+  bool handle_button_release(GdkEventButton *);
+  bool handle_motion_notify(GdkEventMotion *);
+  void handle_drag_data_get(const Glib::RefPtr<Gdk::DragContext>& context, Gtk::SelectionData& selection_data, guint info, guint time);
+  void handle_drag_data_received(const Glib::RefPtr<Gdk::DragContext>& context, int x, int y, Gtk::SelectionData selection_data, guint info, guint time);
+
 
  public:
   bool operator==(const Task &) const;

src/modules/wlr/taskbar.cpp

@@ -251,6 +251,10 @@ static const struct zwlr_foreign_toplevel_handle_v1_listener toplevel_handle_imp
     .parent = tl_handle_parent,
 };
 
+static const std::vector<Gtk::TargetEntry> target_entries = {
+   Gtk::TargetEntry("WAYBAR_TOPLEVEL", Gtk::TARGET_SAME_APP, 0)
+};
+
 Task::Task(const waybar::Bar &bar, const Json::Value &config, Taskbar *tbar,
            struct zwlr_foreign_toplevel_handle_v1 *tl_handle, struct wl_seat *seat)
     : bar_{bar},
@@ -309,9 +313,19 @@ Task::Task(const waybar::Bar &bar, const Json::Value &config, Taskbar *tbar,
   /* Handle click events if configured */
   if (config_["on-click"].isString() || config_["on-click-middle"].isString() ||
       config_["on-click-right"].isString()) {
-    button_.add_events(Gdk::BUTTON_PRESS_MASK);
-    button_.signal_button_press_event().connect(sigc::mem_fun(*this, &Task::handle_clicked), false);
   }
+
+  button_.add_events(Gdk::BUTTON_PRESS_MASK);
+  button_.signal_button_press_event().connect(sigc::mem_fun(*this, &Task::handle_clicked), false);
+  button_.signal_button_release_event().connect(sigc::mem_fun(*this, &Task::handle_button_release), false);
+
+  button_.signal_motion_notify_event().connect(sigc::mem_fun(*this, &Task::handle_motion_notify), false);
+
+  button_.drag_source_set(target_entries, Gdk::BUTTON1_MASK, Gdk::ACTION_MOVE);
+  button_.drag_dest_set(target_entries, Gtk::DEST_DEFAULT_ALL, Gdk::ACTION_MOVE);
+
+  button_.signal_drag_data_get().connect(sigc::mem_fun(*this, &Task::handle_drag_data_get), false);
+  button_.signal_drag_data_received().connect(sigc::mem_fun(*this, &Task::handle_drag_data_received), false);
 }
 
 Task::~Task() {
@@ -495,6 +509,14 @@ void Task::handle_closed() {
 }
 
 bool Task::handle_clicked(GdkEventButton *bt) {
+  /* filter out additional events for double/triple clicks */
+  if (bt->type == GDK_BUTTON_PRESS) {
+    /* save where the button press ocurred in case it becomes a drag */
+    drag_start_button = bt->button;
+    drag_start_x = bt->x;
+    drag_start_y = bt->y;
+  }
+
   std::string action;
   if (config_["on-click"].isString() && bt->button == 1)
     action = config_["on-click"].asString();
@@ -528,6 +550,60 @@ bool Task::handle_clicked(GdkEventButton *bt) {
   return true;
 }
 
+bool Task::handle_button_release(GdkEventButton *bt) {
+  drag_start_button = -1;
+  return false;
+}
+
+bool Task::handle_motion_notify(GdkEventMotion *mn) {
+  if (drag_start_button == -1)
+    return false;
+
+  if ( button_.drag_check_threshold(drag_start_x, drag_start_y, mn->x, mn->y)) {
+    /* start drag in addition to other assigned action */
+    auto target_list = Gtk::TargetList::create(target_entries);
+    auto refptr = Glib::RefPtr<Gtk::TargetList>(target_list);
+    auto drag_context = button_.drag_begin(refptr, Gdk::DragAction::ACTION_MOVE, drag_start_button, (GdkEvent*)mn);
+  }
+
+  return false;
+}
+
+void Task::handle_drag_data_get(const Glib::RefPtr<Gdk::DragContext>& context, Gtk::SelectionData& selection_data, guint info, guint time)
+{
+  spdlog::debug("drag_data_get");
+  void* button_addr = (void*)&this->button_;
+
+  selection_data.set(
+    "WAYBAR_TOPLEVEL",
+    32,
+    (const guchar *)&button_addr,
+    sizeof (gpointer));
+}
+
+void Task::handle_drag_data_received(const Glib::RefPtr<Gdk::DragContext>& context, int x, int y, Gtk::SelectionData selection_data, guint info, guint time)
+{
+  spdlog::debug("drag_data_received");
+  gpointer handle = *(gpointer*)selection_data.get_data();
+  auto dragged_button = (Gtk::Button*)handle;
+
+  if(dragged_button == &this->button_)
+    return;
+
+  auto parent_of_dragged = dragged_button->get_parent();
+  auto parent_of_dest = this->button_.get_parent();
+
+  if(parent_of_dragged != parent_of_dest)
+    return;
+
+  auto box = (Gtk::Box*)parent_of_dragged;
+
+  auto position_prop = box->child_property_position(this->button_);
+  auto position = position_prop.get_value();
+
+  box->reorder_child(*dragged_button, position);
+}
+
 bool Task::operator==(const Task &o) const { return o.id_ == id_; }
 
 bool Task::operator!=(const Task &o) const { return o.id_ != id_; }