Make multidrag a bit more independent of Disobedience

[disorder] / disobedience / multidrag.c

/*
 * This file is part of DisOrder
 * Copyright (C) 2009 Richard Kettlewell
 *
 * 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/>.
 */
/** @file disobedience/multidrag.c
 * @brief Drag multiple rows of a GtkTreeView
 *
 * Normally when you start a drag, GtkTreeView sets the selection to just row
 * you dragged from (because it can't cope with dragging more than one row at a
 * time).
 *
 * Disobedience needs more.  To implement this it intercepts button-press-event
 * and button-release event and for clicks that might be the start of drags,
 * suppresses changes to the selection.  A consequence of this is that it needs
 * to intercept button-release-event too, to restore the effect of the click,
 * if it turns out not to be drag after all.
 *
 * The location of the initial click is stored in object data called @c
 * multidrag-where.
 *
 * Inspired by similar code in <a
 * href="http://code.google.com/p/quodlibet/">Quodlibet</a> (another software
 * jukebox, albeit as far as I can see a single-user one).
 */
#include <config.h>
#include <glib.h>
#include <gtk/gtk.h>

#include "multidrag.h"

static gboolean multidrag_selection_block(GtkTreeSelection attribute((unused)) *selection,
					  GtkTreeModel attribute((unused)) *model,
					  GtkTreePath attribute((unused)) *path,
					  gboolean attribute((unused)) path_currently_selected,
					  gpointer data) {
  return *(const gboolean *)data;
}

static void block_selection(GtkWidget *w, gboolean block,
			    int x, int y) {
  static const gboolean which[] = { FALSE, TRUE };
  GtkTreeSelection *s = gtk_tree_view_get_selection(GTK_TREE_VIEW(w));
  gtk_tree_selection_set_select_function(s,
					 multidrag_selection_block,
					 (gboolean *)&which[!!block],
					 NULL);
  // Remember the pointer location
  int *where = g_object_get_data(G_OBJECT(w), "multidrag-where");
  if(!where) {
    where = g_malloc(2 * sizeof (int));
    g_object_set_data(G_OBJECT(w), "multidrag-where", where);
  }
  where[0] = x;
  where[1] = y;
  // TODO release 'where' when object is destroyed
}

static gboolean multidrag_button_press_event(GtkWidget *w,
					     GdkEventButton *event,
					     gpointer attribute((unused)) user_data) {
  /* By default we assume that anything this button press does should
   * act as normal */
  block_selection(w, TRUE, -1, -1);
  /* We are only interested in left-button behavior */
  if(event->button != 1)
    return FALSE;
  /* We are only interested in unmodified clicks (not SHIFT etc) */
  if(event->state & GDK_MODIFIER_MASK)
    return FALSE;
  /* We are only interested if a well-defined path is clicked */
  GtkTreePath *path;
  if(!gtk_tree_view_get_path_at_pos(GTK_TREE_VIEW(w),
				    event->x, event->y,
				    &path,
				    NULL,
				    NULL, NULL))
    return FALSE;
  //gtk_widget_grab_focus(w);    // TODO why??
  /* We are only interested if a selected row is clicked */
  GtkTreeSelection *s = gtk_tree_view_get_selection(GTK_TREE_VIEW(w));
  if(!gtk_tree_selection_path_is_selected(s, path))
    return FALSE;
  /* We block subsequent selection changes and remember where the
   * click was */
  block_selection(w, FALSE, event->x, event->y);
  return FALSE;			/* propagate */
}

static gboolean multidrag_button_release_event(GtkWidget *w,
					       GdkEventButton *event,
					       gpointer attribute((unused)) user_data) {
  int *where = g_object_get_data(G_OBJECT(w), "multidrag-where");

  /* Did button-press-event do anything?  We just check the outcome rather than
   * going through all the conditions it tests. */
  if(where && where[0] != -1) {
    // Remember where the down-click was
    const int x = where[0], y = where[1];
    // Re-allow selections
    block_selection(w, TRUE, -1, -1);
    if(x == event->x && y == event->y) {
      // If the up-click is at the same location as the down-click,
      // it's not a drag.
      GtkTreePath *path;
      GtkTreeViewColumn *col;
      if(gtk_tree_view_get_path_at_pos(GTK_TREE_VIEW(w),
				       event->x, event->y,
				       &path,
				       &col,
				       NULL, NULL)) {
	gtk_tree_view_set_cursor(GTK_TREE_VIEW(w), path, col, FALSE);
      }
    }
  }
  return FALSE;			/* propagate */
}

/** @brief Allow multi-row drag for @p w
 * @param w A GtkTreeView widget
 *
 * Suppresses the restriction of selections when a drag is started.
 */
void make_treeview_multidrag(GtkWidget *w) {
  g_signal_connect(w, "button-press-event",
		   G_CALLBACK(multidrag_button_press_event), NULL);
  g_signal_connect(w, "button-release-event",
		   G_CALLBACK(multidrag_button_release_event), NULL);
}

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*/