line with outline

[folibis]

I still trying to find the fastest way to draw line with outline. Currently it work with next code:

void TestWidget::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.setRenderHints(QPainter::Antialiasing);
    QPainterPath path;
    path.moveTo(100,50);
    path.lineTo(600,50);
    path.lineTo(700,400);
    path.lineTo(50,400);
    path.moveTo(300,50);
    path.lineTo(300,450);
    QPen pen(QColor(255, 0, 0));
    painter.setPen(pen);
    QBrush brush(QColor(255,255,0));
    painter.setBrush(brush);
    QPainterPathStroker stroker;
    stroker.setWidth(10);
    stroker.setCapStyle(Qt::RoundCap);
    stroker.setJoinStyle(Qt::RoundJoin);
    path = stroker.createStroke(path);
    painter.drawPath(path);
}

void TestWidget::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.setRenderHints(QPainter::Antialiasing);
    QPainterPath path;
    path.moveTo(100,50);
    path.lineTo(600,50);
    path.lineTo(700,400);
    path.lineTo(50,400);
    path.moveTo(300,50);
    path.lineTo(300,450);
    QPen pen(QColor(255, 0, 0));
    painter.setPen(pen);
    QBrush brush(QColor(255,255,0));
    painter.setBrush(brush);
    QPainterPathStroker stroker;
    stroker.setWidth(10);
    stroker.setCapStyle(Qt::RoundCap);
    stroker.setJoinStyle(Qt::RoundJoin);
    path = stroker.createStroke(path);
    painter.drawPath(path);
}

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But how can I remove artefacts inside the lines at connection points? It have to look like roads on a map? without inner cross lines.
path.pngpath.png