Gtk2::Ex::TextView::FollowAppend - variant of TextView following appended text

 use Gtk2::Ex::TextView::FollowAppend;
 my $textview = Gtk2::Ex::TextView::FollowAppend->new;

    Gtk2::Widget
      Gtk2::Container
        Gtk2::TextView
          Gtk2::Ex::TextView::FollowAppend

# Copyright 2009, 2010, 2011 Kevin Ryde

# This file is part of Gtk2-Ex-ErrorTextDialog.
#
# Gtk2-Ex-ErrorTextDialog 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, or (at your option) any
# later version.
#
# Gtk2-Ex-ErrorTextDialog 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 Gtk2-Ex-ErrorTextDialog.  If not, see <http://www.gnu.org/licenses/>.

package Gtk2::Ex::TextView::FollowAppend;
use 5.008;
use strict;
use warnings;
use Gtk2;

# uncomment this to run the ### lines
#use Devel::Comments;

our $VERSION = 10;

use Glib::Object::Subclass
  'Gtk2::TextView',
  signals => { size_allocate => \&_do_size_allocate,
               notify        => \&_do_notify,
               destroy       => \&_do_destroy,
             };

sub new_with_buffer {
  my ($class, $textbuf) = @_;
  return $class->Glib::Object::new (buffer => $textbuf);
}

# 'destroy' class closure
sub _do_destroy {
  my ($self) = @_;
  ### FollowAppend _do_destroy(): "$self"

  # The GtkObjectFlags GTK_IN_DESTRUCTION might do this, if it was exposed
  # at the perl level.  Except gtk_object_dispose() looks like the flag
  # might be set solely while 'destroy' runs, but any notifies during
  # finalize should suppress get_buffer() below too.  Except can finalize
  # emit notify anyway?
  #
  $self->{'destroyed'} = 1;

  $self->signal_chain_from_overridden ();
}

# 'notify' class closure
sub _do_notify {
  my ($self, $pspec) = @_;
  ### FollowAppend _do_notify(): $pspec->get_name
  $self->signal_chain_from_overridden ($pspec);

  # after 'destroy' runs it's important not to call ->get_buffer() since
  # that func creates a new TextBuffer in place of what
  # gtk_text_view_destroy() just destroyed and set to NULL.  If a textbuf is
  # re-created like that it leads to a fatal error in
  # gtk_text_view_finalize().
  #
  if (! $self->{'destroyed'} && $pspec->get_name eq 'buffer') {
    require Glib::Ex::SignalIds;
    require Scalar::Util;

    my $textbuf = $self->get_buffer;
    Scalar::Util::weaken (my $weak_self = $self);
    my $ref_weak_self = \$weak_self;

    $self->{'textbuf_ids'} = $textbuf && Glib::Ex::SignalIds->new
      ($textbuf,
       $textbuf->signal_connect_after ('insert-text',
                                       \&_do_textbuf_insert,
                                       $ref_weak_self),
       $textbuf->signal_connect_after ('insert-pixbuf',
                                       \&_do_textbuf_insert_pixbuf_or_anchor,
                                       $ref_weak_self),
       $textbuf->signal_connect_after ('insert-child-anchor',
                                       \&_do_textbuf_insert_pixbuf_or_anchor,
                                       $ref_weak_self));
  }
}

# 'size-allocate' class closure
sub _do_size_allocate {
  my ($self, $alloc) = @_;
  ### FollowAppend size_allocate: $alloc->x.",".$alloc->y." ".$alloc->width."x".$alloc->height

  my $want_follow = _want_follow ($self);
  ### $want_follow

  $self->signal_chain_from_overridden ($alloc);

  if ($want_follow) {
    ### _do_size_allocate() scroll_to_mark
    $self->scroll_to_mark ($self->get_buffer->get_insert, 0, 0, 0,0);
  }
}

# 'insert-pixbuf' and 'insert-child-anchor' signal handler on textbuf
sub _do_textbuf_insert_pixbuf_or_anchor {
  my ($textbuf, $iter, $pixbuf_or_anchor, $ref_weak_self) = @_;
  _do_textbuf_insert ($textbuf, $iter, undef, 1, $ref_weak_self);
}

# 'insert-text' signal handler on textbuf,
# plus fakery from 'insert-pixbuf' and 'insert-child-anchor' above
sub _do_textbuf_insert {
  my ($textbuf, $iter, $text, $textlen, $ref_weak_self) = @_;
  my $self = $$ref_weak_self || return;
  ### FollowAppend _do_textbuf_insert() iter: $iter->get_offset
  ### $textlen
  ### $text

  if ($iter->is_end
      && _want_follow ($self,
                       $textbuf->get_iter_at_offset
                       ($iter->get_offset - $textlen))) {
    ### _do_textbuf_insert() scroll_to_mark
    $self->scroll_to_mark ($textbuf->get_insert, 0, 0, 0,0);
  }
}

sub _want_follow {
  my ($self, $insert_iter) = @_;
  my $textbuf = $self->get_buffer;
  my $cursor_iter = $textbuf->get_iter_at_mark ($textbuf->get_insert);

  ### insert at: ($insert_iter||$textbuf->get_end_iter)->get_offset
  ### end: $textbuf->get_end_iter->get_offset
  ### cursor: $cursor_iter->get_offset
  ### charcount: $textbuf->get_char_count
  ### cursor is_end: $cursor_iter->is_end

  return ($cursor_iter->is_end
          && _iter_is_visible ($self, $insert_iter||$textbuf->get_end_iter));
}

# return true if $iter is visible in $textview
# partially visible $iter pos returns true
sub _iter_is_visible {
  my ($textview, $iter) = @_;
  my $visible_rect = $textview->get_visible_rect;

  ###
  ### visible rect: $visible_rect->x.",".$visible_rect->y." ".$visible_rect->width."x".$visible_rect->height." height to ".($visible_rect->y+$visible_rect->height)
  ### iter: $iter->get_offset
  ### start_vis: do { my $start_iter = $textview->get_iter_at_location (0, $visible_rect->y); $start_iter->get_offset }
  ### end vis: do { my $end_iter = $textview->get_iter_at_location (0, $visible_rect->y + $visible_rect->height); $end_iter->get_offset }
  ### end buf: $textview->get_buffer->get_char_count

  my $start_iter = $textview->get_iter_at_location(0, $visible_rect->y);
  if ($iter->compare($start_iter) < 0) {
    # $iter is before start of visible part
    return 0;
  }
  my $end_iter = $textview->get_iter_at_location
    (0, $visible_rect->y + $visible_rect->height - 1);
  $end_iter->forward_visible_line;
  # true if iter is at or before end of visible part
  return ($iter->compare($end_iter) <= 0);
}

# This version based on get_iter_location() for the rectangle of the target
# iter, where the above only asks for the iter extents of the visible
# window.  Will the above help with lazy calculation of lines, or does
# everything have to be calculated anyway for the total size for the
# scrollbar etc?
#
# # return true if $iter is visible in $textview
# sub _iter_is_visible {
#   my ($textview, $iter) = @_;
#   my $visible_rect = $textview->get_visible_rect;
#   my $iter_rect = $textview->get_iter_location ($iter);
#   if (DEBUG) { print "  visible rect ",
#                  $visible_rect->x,",",$visible_rect->y," ",
#                    $visible_rect->width,"x",$visible_rect->height,
#                      " height to ",$visible_rect->y+$visible_rect->height,"\n";
#                print "  iter rect ",
#                  $iter_rect->x,",",$iter_rect->y," ",
#                    $iter_rect->width,"x",$iter_rect->height,
#                      " height to ",$iter_rect->y+$iter_rect->height,"\n";
#              }
# 
#   # if y1+h1 < y2 then rect1 is entirely above rect2, or if y2+h2 < y1 then
#   # rect2 is entirely above rect1; if neither then there's overlap
#   # rect_overlaps_rect() ?
#   return ! ($visible_rect->y + $visible_rect->height < $iter_rect->y
#             || $iter_rect->y + $iter_rect->height < $visible_rect->y);
# }

1;
__END__