scrolledwindow: Add ::edge-overshot signal

This signal is emitted whenever user scrolling hits the overshoot
edge in the given direction. May be useful to add "reload" or "load
more" behaviors in apps.

https://bugzilla.gnome.org/show_bug.cgi?id=738534

gtk/gtkscrolledwindow.c

@@ -208,6 +208,7 @@ enum
 {
   SCROLL_CHILD,
   MOVE_FOCUS_OUT,
+  EDGE_OVERSHOT,
   LAST_SIGNAL
 };
 
@@ -546,6 +547,32 @@ gtk_scrolled_window_class_init (GtkScrolledWindowClass *class)
                   G_TYPE_NONE, 1,
                   GTK_TYPE_DIRECTION_TYPE);
 
+  /**
+   * GtkScrolledWindow::edge-overshot:
+   * @scrolled_window: a #GtkScrolledWindow
+   * @pos: edge side that was hit
+   *
+   * The ::edge-overshot signal is emitted whenever user initiated scrolling
+   * makes the scrolledwindow firmly surpass (ie. with some edge resistance)
+   * the lower or upper limits defined by the adjustment in that orientation.
+   *
+   * If a similar behavior without edge resistance is desired, one alternative
+   * may be to check on #GtkAdjustment::value-changed that the value equals
+   * either #GtkAdjustment:lower or #GtkAdjustment:upper - #GtkAdjustment:page-size.
+   *
+   * Note: The @pos argument is LTR/RTL aware, so callers should be aware too
+   * if intending to provide behavior on horizontal edges.
+   *
+   * Since: 3.16
+   */
+  signals[EDGE_OVERSHOT] =
+    g_signal_new (I_("edge-overshot"),
+                  G_TYPE_FROM_CLASS (gobject_class),
+                  G_SIGNAL_RUN_LAST, 0,
+                  NULL, NULL,
+                  g_cclosure_marshal_generic,
+                  G_TYPE_NONE, 1, GTK_TYPE_POSITION_TYPE);
+
   binding_set = gtk_binding_set_by_class (class);
 
   add_scroll_binding (binding_set, GDK_KEY_Left,  GDK_CONTROL_MASK, GTK_SCROLL_STEP_BACKWARD, TRUE);
@@ -2525,20 +2552,46 @@ _gtk_scrolled_window_set_adjustment_value (GtkScrolledWindow *scrolled_window,
 {
   GtkScrolledWindowPrivate *priv = scrolled_window->priv;
   gdouble lower, upper, *prev_value;
+  GtkPositionType edge_pos;
+  gboolean vertical;
 
   lower = gtk_adjustment_get_lower (adjustment) - MAX_OVERSHOOT_DISTANCE;
   upper = gtk_adjustment_get_upper (adjustment) -
     gtk_adjustment_get_page_size (adjustment) + MAX_OVERSHOOT_DISTANCE;
 
   if (adjustment == gtk_range_get_adjustment (GTK_RANGE (priv->hscrollbar)))
-    prev_value = &priv->unclamped_hadj_value;
+    vertical = FALSE;
   else if (adjustment == gtk_range_get_adjustment (GTK_RANGE (priv->vscrollbar)))
-    prev_value = &priv->unclamped_vadj_value;
+    vertical = TRUE;
   else
     return;
 
-  *prev_value = CLAMP (value, lower, upper);
+  if (vertical)
+    prev_value = &priv->unclamped_vadj_value;
+  else
+    prev_value = &priv->unclamped_hadj_value;
+
+  value = CLAMP (value, lower, upper);
+
+  if (*prev_value == value)
+    return;
+
+  *prev_value = value;
   gtk_adjustment_set_value (adjustment, value);
+
+  if (value == lower)
+    edge_pos = vertical ? GTK_POS_TOP : GTK_POS_LEFT;
+  else if (value == upper)
+    edge_pos = vertical ? GTK_POS_BOTTOM : GTK_POS_RIGHT;
+  else
+    return;
+
+  /* Invert horizontal edge position on RTL */
+  if (!vertical &&
+      gtk_widget_get_direction (GTK_WIDGET (scrolled_window)) == GTK_TEXT_DIR_RTL)
+    edge_pos = (edge_pos == GTK_POS_LEFT) ? GTK_POS_RIGHT : GTK_POS_LEFT;
+
+  g_signal_emit (scrolled_window, signals[EDGE_OVERSHOT], 0, edge_pos);
 }
 
 static gboolean

tests/Makefile.am

@@ -133,6 +133,7 @@ noinst_PROGRAMS =  $(TEST_PROGS)	\
 	testexpander			\
 	testvolumebutton		\
 	testscrolledwindow		\
+	testscrolledge			\
 	testswitch			\
 	testcellarea			\
 	testswitch			\
@@ -270,6 +271,7 @@ testgrouping_DEPENDENCIES = $(TEST_DEPS)
 testtooltips_DEPENDENCIES = $(TEST_DEPS)
 testvolumebutton_DEPENDENCIES = $(TEST_DEPS)
 testscrolledwindow_DEPENDENCIES = $(TEST_DEPS)
+testscrolledge_DEPENDENCIES = $(TEST_DEPS)
 testcellarea_DEPENDENCIES = $(TEST_DEPS)
 testtreemenu_DEPENDENCIES = $(TEST_DEPS)
 testwindows_DEPENDENCIES = $(TEST_DEPS)

tests/testscrolledge.c

@@ -0,0 +1,129 @@
+/* testscrolledge.c
+ *
+ * Copyright (C) 2014 Matthias Clasen <mclasen@redhat.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <gtk/gtk.h>
+
+static guint add_rows_id = 0;
+
+static void
+populate_list (GtkListBox *list)
+{
+  gint i;
+  gchar *text;
+  GtkWidget *row, *label;
+  gint n;
+  GList *l;
+
+  l = gtk_container_get_children (GTK_CONTAINER (list));
+  n = g_list_length (l);
+  g_list_free (l);
+
+  for (i = 1; i <= 50; i++)
+    {
+      row = gtk_list_box_row_new ();
+      text = g_strdup_printf ("List row %d", i + n);
+      label = gtk_label_new (text);
+      g_free (text);
+
+      g_object_set (label, "margin", 10, NULL);
+      gtk_widget_set_halign (label, GTK_ALIGN_START);
+      gtk_container_add (GTK_CONTAINER (row), label);
+      gtk_widget_show_all (row);
+      gtk_container_add (GTK_CONTAINER (list), row);
+    }
+}
+
+static GtkWidget *popup;
+static GtkWidget *spinner;
+
+static gboolean
+add_rows (gpointer data)
+{
+  GtkListBox *list = data;
+
+  gtk_widget_hide (popup);
+  gtk_spinner_stop (GTK_SPINNER (spinner));
+
+  populate_list (list);
+  add_rows_id = 0;
+
+  return G_SOURCE_REMOVE;
+}
+
+static void
+edge_overshot (GtkScrolledWindow *sw,
+               GtkPositionType    pos,
+               GtkListBox        *list)
+{
+  if (pos == GTK_POS_BOTTOM)
+    {
+      gtk_spinner_start (GTK_SPINNER (spinner));
+      gtk_widget_show (popup);
+
+      if (add_rows_id == 0)
+        add_rows_id = g_timeout_add (2000, add_rows, list);
+    }
+}
+
+int
+main (int argc, char *argv[])
+{
+  GtkWidget *win;
+  GtkWidget *sw;
+  GtkWidget *list;
+  GtkWidget *overlay;
+  GtkWidget *label;
+
+  gtk_init (NULL, NULL);
+
+  win = gtk_window_new (GTK_WINDOW_TOPLEVEL);
+  gtk_window_set_default_size (GTK_WINDOW (win), 600, 400);
+
+  overlay = gtk_overlay_new ();
+  popup = gtk_box_new (GTK_ORIENTATION_HORIZONTAL, 10);
+  gtk_widget_set_halign (popup, GTK_ALIGN_CENTER);
+  gtk_widget_set_valign (popup, GTK_ALIGN_END);
+  g_object_set (popup, "margin", 40, NULL);
+  label = gtk_label_new ("Getting more rows...");
+  spinner = gtk_spinner_new ();
+  gtk_widget_show (spinner);
+  gtk_widget_show (label);
+  gtk_container_add (GTK_CONTAINER (popup), label);
+  gtk_container_add (GTK_CONTAINER (popup), spinner);
+
+  gtk_overlay_add_overlay (GTK_OVERLAY (overlay), popup);
+  gtk_widget_set_no_show_all (popup, TRUE);
+
+  sw = gtk_scrolled_window_new (NULL, NULL);
+  gtk_scrolled_window_set_policy (GTK_SCROLLED_WINDOW (sw), GTK_POLICY_NEVER, GTK_POLICY_AUTOMATIC);
+  list = gtk_list_box_new ();
+  gtk_list_box_set_selection_mode (GTK_LIST_BOX (list), GTK_SELECTION_NONE);
+
+  gtk_container_add (GTK_CONTAINER (win), overlay);
+  gtk_container_add (GTK_CONTAINER (overlay), sw);
+  gtk_container_add (GTK_CONTAINER (sw), list);
+  populate_list (GTK_LIST_BOX (list));
+
+  g_signal_connect (sw, "edge-overshot", G_CALLBACK (edge_overshot), list);
+
+  gtk_widget_show_all (win);
+
+  gtk_main ();
+
+  return 0;
+}