Method paintEvent

lib/QCodeEditor/src/internal/QLineNumberArea.cpp:69–121

}

void QLineNumberArea::paintEvent(QPaintEvent *event)
{
  QPainter painter(this);
  painter.setLayoutDirection(Qt::LeftToRight);

  // Clearing rect to update
  painter.fillRect(event->rect(),
                   m_syntaxStyle->getFormat("Text").background().color());

  auto blockNumber = m_codeEditParent->getFirstVisibleBlock();
  auto block = m_codeEditParent->document()->findBlockByNumber(blockNumber);
  auto top = (int)m_codeEditParent->document()
                 ->documentLayout()
                 ->blockBoundingRect(block)
                 .translated(0, -m_codeEditParent->verticalScrollBar()->value())
                 .top();
  auto bottom = top
                + (int)m_codeEditParent->document()
                      ->documentLayout()
                      ->blockBoundingRect(block)
                      .height();

  auto currentLine
      = m_syntaxStyle->getFormat("CurrentLineNumber").foreground().color();
  auto otherLines = m_syntaxStyle->getFormat("LineNumber").foreground().color();

  painter.setFont(m_codeEditParent->font());

  while (block.isValid() && top <= event->rect().bottom())
  {
    if (block.isVisible() && bottom >= event->rect().top())
    {
      QString number = QString::number(blockNumber + 1);

      auto isCurrentLine
          = m_codeEditParent->textCursor().blockNumber() == blockNumber;
      painter.setPen(isCurrentLine ? currentLine : otherLines);

      painter.drawText(-5, top, sizeHint().width(),
                       m_codeEditParent->fontMetrics().height(), Qt::AlignRight,
                       number);
    }

    block = block.next();
    top = bottom;
    bottom = top
             + (int)m_codeEditParent->document()
                   ->documentLayout()
                   ->blockBoundingRect(block)
                   .height();
    ++blockNumber;
  }
}