[gtkmm] Flickering TextView in ScrolledWindow

[Morten Brix Pedersen <morten wtf dk>]

Hi,

I'm porting my application to gtkmm2, which means that I'm replacing
Gtk::Text with Gtk::TextView. However, the code used to scroll down
automatically flickers the screen.

It didn't happen when a Gtk::Text was used instead. Simple case below.

Thanks.

  - Morten.

#include <gtkmm/window.h>
#include <gtkmm/button.h>
#include <gtkmm/textview.h>
#include <gtkmm/textbuffer.h>
#include <gtkmm/scrolledwindow.h>
#include <gtkmm/box.h>
#include <gtkmm/main.h>

class AppWindow : public Gtk::Window
{
public:
    AppWindow();
    virtual ~AppWindow() { }

    void insertText();

protected:
    Gtk::TextView _textview;
    Gtk::ScrolledWindow _swin;
    Gtk::Button _button;
    Gtk::VBox _vbox;
};

AppWindow::AppWindow()
    : _button("Insert text")
{
    set_default_size(600, 400);

    _button.signal_clicked().connect(slot(*this, &AppWindow::insertText));

    _swin.add(_textview);

    _vbox.pack_start(_swin);
    _vbox.pack_start(_button, Gtk::SHRINK);

    add(_vbox);
    show_all();
}

void AppWindow::insertText()
{
    // see if the scrollbar is located in the bottom, then we need to scroll
    // after insert 
    bool scroll = false;
    if (_swin.get_vadjustment()->get_value() + _swin.get_vadjustment()->get_page_size() == _swin.get_vadjustment()->get_upper())
          scroll = true;

    // insert the text at the end
    Gtk::TextIter iter = _textview.get_buffer()->get_end_iter();
    _textview.get_buffer()->insert(iter, "Hello World - this is a test to see how inserted text flickers in the scrolledwindow!\n");

    // finally scroll down; this causes the widget to flicker
    if (scroll)
          _swin.get_vadjustment()->set_value(_swin.get_vadjustment()->get_upper());
}

int main (int argc, char *argv[])
{
    Gtk::Main kit(argc, argv);

    AppWindow window;
    kit.run(window);

    return 0;
}