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Edit::Edit(QWidget *parent)
  : QTextEdit(parent)
{
  setViewportMargins(50, 0, 0, 0);
	
  connect(verticalScrollBar(), SIGNAL(valueChanged(int)), this, SLOT(update()));
  connect(this, SIGNAL(textChanged()), this, SLOT(update()));
}

bool Edit::event(QEvent *event) {
  if (event->type()==QEvent::Paint) {
    QPainter p(this);
    p.fillRect(0, 0, 50, height(), QColor(255, 255, 192));
		
    int contentsY = verticalScrollBar()->value();
    qreal pageBottom = contentsY+viewport()->height();
    int m_lineNumber(1);
    const QFontMetrics fm=fontMetrics();
    const int ascent = fontMetrics().ascent() +1;
		
    for (QTextBlock block=document()->begin(); block.isValid(); block=block.next(), m_lineNumber++) {
      QTextLayout *layout = block.layout();
      const QRectF boundingRect = layout->boundingRect();
      QPointF position = layout->position();
      if ( position.y() +boundingRect.height() < contentsY ) {
        continue;
      }
      if ( position.y() > pageBottom ) {
        break;
      }
      const QString txt = QString::number(m_lineNumber);
      p.drawText(50-fm.width(txt)-2, qRound(position.y())-contentsY+ascent, txt); 
      }
    }

    return QTextEdit::event(event);
}