QLineF line(sourcePoint, destPoint);
QLinearGradient gradient(sourcePoint.x(), sourcePoint.y(), destPoint.x(), destPoint.y());
gradient.setColorAt(0.0, Qt::white);
gradient.setColorAt(0.5, color);
gradient.setColorAt(1.0, Qt::black);
painter->setPen(QPen(QBrush(gradient), width, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));
painter->drawLine(line);