[gnome-panel/wip-geiger-dialog: 137/138] properties-dialog: add drag-and-drop to applet list

[Sebastian Geiger <segeiger src gnome org>]

commit 434bd7e6e45fca79b9c37eb177dc6640a93aced9
Author: Sebastian Geiger <sbastig gmx net>
Date:   Sun Apr 19 21:20:46 2020 +0200

    properties-dialog: add drag-and-drop to applet list
    
    Functionality to update applet position on panel is still missing.

 data/theme/common.css            |  4 ++
 gnome-panel/gp-applet-list-row.c | 93 ++++++++++++++++++++++++++++++++--------
 2 files changed, 78 insertions(+), 19 deletions(-)
---
diff --git a/data/theme/common.css b/data/theme/common.css
index c1f63c3de..2b2a1d075 100644
--- a/data/theme/common.css
+++ b/data/theme/common.css
@@ -111,3 +111,7 @@ gp-handle {
 .context-row {
   padding: 4px 10px;
 }
+
+.applet-list-row-drag-icon {
+  background-color: #ffffff;
+}
diff --git a/gnome-panel/gp-applet-list-row.c b/gnome-panel/gp-applet-list-row.c
index 893f67c24..233cf9c70 100644
--- a/gnome-panel/gp-applet-list-row.c
+++ b/gnome-panel/gp-applet-list-row.c
@@ -53,6 +53,10 @@ enum
 
 static GParamSpec *row_properties[LAST_PROP] = { NULL };
 
+static GtkTargetEntry entries[] = {
+    { (gchar *)"GTK_LIST_BOX_ROW", GTK_TARGET_SAME_APP, 0 }
+};
+
 G_DEFINE_TYPE (GpAppletListRow, gp_applet_list_row, GTK_TYPE_LIST_BOX_ROW)
 
 static void
@@ -139,41 +143,92 @@ drag_data_get_cb (GtkWidget        *widget,
                   GpAppletListRow  *self)
 {
   gtk_selection_data_set (data,
-                          gtk_selection_data_get_target (data),
+                          gdk_atom_intern_static_string ("GTK_LIST_BOX_ROW"),
                           8,
-                          (const guchar *) self->iid,
-                          strlen (self->iid));
+                          (const guchar *)&widget,
+                          sizeof (gpointer));
 }
 
 static void
-setup_drag_source (GpAppletListRow *self)
+drag_data_received_cb (GtkWidget        *target,
+                       GdkDragContext   *context,
+                       gint              x,
+                       gint              y,
+                       GtkSelectionData *selection_data,
+                       guint             info,
+                       guint             time,
+                       gpointer          user_data)
 {
-  GpAppletInfo *info;
-  GdkModifierType modifiers;
-  GdkDragAction actions;
-  GtkTargetList *target_list;
-  GdkAtom target;
+  gpointer handle;
+  GtkWidget *source;
+  GtkWidget *source_list;
+  GtkWidget *target_list;
+  int position;
 
-  info = gp_module_get_applet_info (self->module, self->applet_id, NULL);
+  handle = *(gpointer*) gtk_selection_data_get_data (selection_data);
+  source = gtk_widget_get_ancestor (handle, GTK_TYPE_LIST_BOX_ROW);
 
-  modifiers = GDK_BUTTON1_MASK | GDK_BUTTON2_MASK;
-  actions = GDK_ACTION_COPY;
+  if (source == target)
+    return;
 
-  gtk_drag_source_set (self->event_box, modifiers, NULL, 0, actions);
-  gtk_drag_source_set_icon_name (self->event_box, info->icon_name);
+  source_list = gtk_widget_get_parent (source);
+  target_list = gtk_widget_get_parent (target);
+  position = gtk_list_box_row_get_index (GTK_LIST_BOX_ROW (target));
 
-  target_list = gtk_target_list_new (NULL, 0);
+  g_object_ref (source);
+
+  gtk_container_remove (GTK_CONTAINER (source_list), source);
+  gtk_list_box_insert (GTK_LIST_BOX (target_list), source, position);
+  g_object_unref (source);
+}
+
+static void
+drag_begin (GtkWidget      *widget,
+            GdkDragContext *context,
+            gpointer        user_data)
+{
+  GtkWidget *row;
+  GtkAllocation alloc;
+  cairo_surface_t *surface;
+  cairo_t *cr;
+  GtkStyleContext *style_context;
 
-  target = gdk_atom_intern_static_string ("application/x-panel-applet-iid");
-  gtk_target_list_add (target_list, target, 0, 0);
+  row = gtk_widget_get_ancestor (widget, GTK_TYPE_LIST_BOX_ROW);
+  gtk_widget_get_allocation (row, &alloc);
+  surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32,
+                                        alloc.width, alloc.height);
 
-  gtk_drag_source_set_target_list (self->event_box, target_list);
-  gtk_target_list_unref (target_list);
+  cr = cairo_create (surface);
+
+  style_context = gtk_widget_get_style_context (row);
+  gtk_style_context_add_class (style_context, "applet-list-row-drag-icon");
+  gtk_widget_draw (row, cr);
+  gtk_style_context_remove_class (style_context, "applet-list-row-drag-icon");
+
+  gtk_drag_set_icon_surface (context, surface);
+
+  cairo_destroy (cr);
+  cairo_surface_destroy (surface);
+}
+
+static void
+setup_drag_source (GpAppletListRow *self)
+{
+  gtk_drag_source_set (self->event_box, GDK_BUTTON1_MASK, entries, 1, GDK_ACTION_MOVE);
+  gtk_drag_dest_set (GTK_WIDGET (self), GTK_DEST_DEFAULT_ALL, entries, 1, GDK_ACTION_MOVE);
 
   g_signal_connect (self->event_box,
                     "drag-data-get",
                     G_CALLBACK (drag_data_get_cb),
                     self);
+
+  g_signal_connect (self,
+                    "drag-data-received",
+                    G_CALLBACK (drag_data_received_cb),
+                    NULL);
+
+  g_signal_connect_after (self->event_box, "drag-begin",
+                          G_CALLBACK (drag_begin), NULL);
 }
 
 static void