function drawCallback(canvas, cr, width, height) {
    cr.save();
    cr.setOperator(Cairo.Operator.CLEAR);
    cr.paint();
    cr.restore();

    cr.scale (width, height);
    cr.arc(0.5, 0.5, 0.5, 0, Math.PI * 2);
    cr.setOperator (Cairo.Operator.OVER);
    Gdk.cairo_set_source_pixbuf(cr, pixbuf, 0, 0);
    cr.fill();

    return true;
}