gtk-demo additions

[Matthias Clasen <maclas gmx de>]

There has been some talk about gtk-demo additions recently.
Here is a proposal for a demo showing how to implement simple hypertext
functionality using tags. The code was inspired by similar code in
gucharmap. If you think this is "great example code", I can integrate it
in gtk-demo.

Matthias

#include <gtk/gtk.h>
#include <gdk/gdkkeysyms.h>

static void 
insert_link (GtkTextBuffer *buffer, 
	     GtkTextIter   *iter, 
	     gchar         *text, 
	     gint           page)
{
  GtkTextTag *tag;
  
  tag = gtk_text_buffer_create_tag (buffer, NULL, 
				    "foreground", "blue", 
				    "underline", PANGO_UNDERLINE_SINGLE, 
				    NULL);
  g_object_set_data (G_OBJECT (tag), "page", GINT_TO_POINTER (page));
  gtk_text_buffer_insert_with_tags (buffer, iter, text, -1, tag, NULL);
}

static void
show_page (GtkTextBuffer *buffer, 
	   gint           page)
{
  GtkTextIter iter;

  gtk_text_buffer_set_text (buffer, "", 0);
  gtk_text_buffer_get_iter_at_offset (buffer, &iter, 0);
  if (page == 1)
    {
      gtk_text_buffer_insert (buffer, &iter, "Some text to show that simple ", -1);
      insert_link (buffer, &iter, "hypertext", 3);
      gtk_text_buffer_insert (buffer, &iter, " can easily be realized with ", -1);
      insert_link (buffer, &iter, "tags", 2);
      gtk_text_buffer_insert (buffer, &iter, ".", -1);
    }
  else if (page == 2)
    {
      gtk_text_buffer_insert (buffer, &iter, 
			      "A tag is an attribute that can be applied to some range of text. "
			      "For example, a tag might be called \"bold\" and make the text inside "
			      "the tag bold. However, the tag concept is more general than that; "
			      "tags don't have to affect appearance. They can instead affect the "
			      "behavior of mouse and key presses, \"lock\" a range of text so the "
			      "user can't edit it, or countless other things.\n", -1);
      insert_link (buffer, &iter, "Go back", 1);
    }
  else if (page == 3) 
    {
      GtkTextTag *tag;
  
      tag = gtk_text_buffer_create_tag (buffer, NULL, 
					"weight", PANGO_WEIGHT_BOLD, 
					NULL);
      gtk_text_buffer_insert_with_tags (buffer, &iter, "hypertext:\n", -1, tag, NULL);
      gtk_text_buffer_insert (buffer, &iter, 
			      "machine-readable text that is not sequential but is organized "
			      "so that related items of information are connected.\n", -1);
      insert_link (buffer, &iter, "Go back", 1);
    }
}

static void
follow_if_link (GtkWidget   *text_view, 
		GtkTextIter *iter)
{
  GSList *tags = NULL, *tagp = NULL;

  tags = gtk_text_iter_get_tags (iter);
  for (tagp = tags;  tagp != NULL;  tagp = tagp->next)
    {
      GtkTextTag *tag = tagp->data;
      gint page = GPOINTER_TO_INT (g_object_get_data (G_OBJECT (tag), "page"));

      if (page != 0)
        {
	  show_page (gtk_text_view_get_buffer (GTK_TEXT_VIEW (text_view)), page);
	  break;
        }
    }

  if (tags) 
    g_slist_free (tags);
}

static gboolean
key_press_event (GtkWidget *text_view,
		 GdkEventKey *event)
{
  GtkTextIter iter;
  GtkTextBuffer *buffer;

  switch (event->keyval)
    {
      case GDK_Return: 
      case GDK_KP_Enter:
        buffer = gtk_text_view_get_buffer (GTK_TEXT_VIEW (text_view));
        gtk_text_buffer_get_iter_at_mark (buffer, &iter, 
                                          gtk_text_buffer_get_insert (buffer));
        follow_if_link (text_view, &iter);
        break;

      default:
        break;
    }

  return FALSE;
}

static gboolean
event_after (GtkWidget *text_view,
	     GdkEvent  *ev)
{
  GtkTextIter start, end, iter;
  GtkTextBuffer *buffer;
  GdkEventButton *event;
  gint x, y;

  if (ev->type != GDK_BUTTON_RELEASE)
    return FALSE;

  event = (GdkEventButton *)ev;

  if (event->button != 1)
    return FALSE;

  buffer = gtk_text_view_get_buffer (GTK_TEXT_VIEW (text_view));

  /* we shouldn't follow a link if the user has selected something */
  gtk_text_buffer_get_selection_bounds (buffer, &start, &end);
  if (gtk_text_iter_get_offset (&start) != gtk_text_iter_get_offset (&end))
    return FALSE;

  gtk_text_view_window_to_buffer_coords (GTK_TEXT_VIEW (text_view), 
                                         GTK_TEXT_WINDOW_WIDGET,
                                         event->x, event->y, &x, &y);

  gtk_text_view_get_iter_at_location (GTK_TEXT_VIEW (text_view), &iter, x, y);

  follow_if_link (text_view, &iter);

  return FALSE;
}

gboolean hovering_over_link = FALSE;
GdkCursor *hand_cursor = NULL;
GdkCursor *regular_cursor = NULL;

static void
set_cursor_if_appropriate (GtkTextView    *text_view,
                           gint            x,
                           gint            y)
{
  GSList *tags = NULL, *tagp = NULL;
  GtkTextBuffer *buffer;
  GtkTextIter iter;
  gboolean hovering = FALSE;

  buffer = gtk_text_view_get_buffer (text_view);

  gtk_text_view_get_iter_at_location (text_view, &iter, x, y);
  
  tags = gtk_text_iter_get_tags (&iter);
  for (tagp = tags;  tagp != NULL;  tagp = tagp->next)
    {
      GtkTextTag *tag = tagp->data;
      gint page = GPOINTER_TO_INT (g_object_get_data (G_OBJECT (tag), "page"));

      if (page != 0) 
        {
          hovering = TRUE;
          break;
        }
    }

  if (hovering != hovering_over_link)
    {
      hovering_over_link = hovering;

      if (hovering_over_link)
        gdk_window_set_cursor (gtk_text_view_get_window (text_view, GTK_TEXT_WINDOW_TEXT), hand_cursor);
      else
        gdk_window_set_cursor (gtk_text_view_get_window (text_view, GTK_TEXT_WINDOW_TEXT), regular_cursor);
    }

  if (tags) 
    g_slist_free (tags);
}

static gboolean
motion_notify_event (GtkWidget      *text_view,
		     GdkEventMotion *event)
{
  gint x, y;

  gtk_text_view_window_to_buffer_coords (GTK_TEXT_VIEW (text_view), 
                                         GTK_TEXT_WINDOW_WIDGET,
                                         event->x, event->y, &x, &y);

  set_cursor_if_appropriate (GTK_TEXT_VIEW (text_view), x, y);

  gdk_window_get_pointer (text_view->window, NULL, NULL, NULL);
  return FALSE;
}


static gboolean
visibility_notify_event (GtkWidget          *text_view,
			 GdkEventVisibility *event)
{
  gint wx, wy, bx, by;
  
  gdk_window_get_pointer (text_view->window, &wx, &wy, NULL);
  
  gtk_text_view_window_to_buffer_coords (GTK_TEXT_VIEW (text_view), 
                                         GTK_TEXT_WINDOW_WIDGET,
                                         wx, wy, &bx, &by);

  set_cursor_if_appropriate (GTK_TEXT_VIEW (text_view), bx, by);

  return FALSE;
}

GtkWidget *
do_hypertext (void)
{
  static GtkWidget *window = NULL;

  if (!window)
    {
      GtkWidget *view;
      GtkWidget *sw;
      GtkTextBuffer *buffer;

      hand_cursor = gdk_cursor_new (GDK_HAND2);
      regular_cursor = gdk_cursor_new (GDK_XTERM);
      
      window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
      gtk_window_set_default_size (GTK_WINDOW (window),
				   450, 450);
      
      g_signal_connect (window, "destroy",
			G_CALLBACK (gtk_widget_destroyed), &window);

      gtk_window_set_title (GTK_WINDOW (window), "Hypertext");
      gtk_container_set_border_width (GTK_CONTAINER (window), 0);

      view = gtk_text_view_new ();
      gtk_text_view_set_wrap_mode (GTK_TEXT_VIEW (view), GTK_WRAP_WORD);
      g_signal_connect (G_OBJECT (view), "key-press-event", 
			G_CALLBACK (key_press_event), NULL);
      g_signal_connect (G_OBJECT (view), "event-after", 
			G_CALLBACK (event_after), NULL);
      g_signal_connect (G_OBJECT (view), "motion-notify-event", 
			G_CALLBACK (motion_notify_event), NULL);
      g_signal_connect (G_OBJECT (view), "visibility-notify-event", 
			G_CALLBACK (visibility_notify_event), NULL);

      buffer = gtk_text_view_get_buffer (GTK_TEXT_VIEW (view));
      
      sw = gtk_scrolled_window_new (NULL, NULL);
      gtk_scrolled_window_set_policy (GTK_SCROLLED_WINDOW (sw),
				      GTK_POLICY_AUTOMATIC,
				      GTK_POLICY_AUTOMATIC);
      gtk_container_add (GTK_CONTAINER (window), sw);
      gtk_container_add (GTK_CONTAINER (sw), view);

      show_page (buffer, 1);

      gtk_widget_show_all (sw);
    }

  if (!GTK_WIDGET_VISIBLE (window))
    {
      gtk_widget_show (window);
    }
  else
    {
      gtk_widget_destroy (window);
      window = NULL;
    }

  return window;
}

int
main (int argc, char *argv[])
{
  GtkWidget *text_view;

  gtk_init (&argc, &argv);

  text_view = do_hypertext ();

  gtk_main ();

  return 0;
}