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

[wysota]

QPainterPath::simplified()

[folibis]

Yes, thanks for this tip, it was very useful.
But I found that QPainterPath::simplified() is very very very slow!
For now I found 3 ways to draw line with outline.
1. draw line (QPainter::drawLine) with outline color and width X. then draw the same line with background color and width = X - borderWidth * 2
2. the same way as 1 but using QPainterPath (QPainter::drawPath)
3. draw path from QPainterPath::simplified()

in attachment there are 2 screenshots of all ways.

Expended time:
1. ~ 80 msec.
2. ~ 400 msec.
3. ~ 5000 msec!!

So what, first way seems to be very fast but whet I draw thousands of lines it is not fast enough. And knowing the fact I do double work hurts me.

[ChrisW67]

QPainterPath::simplified() also gives you a different result, obviously fewer isolated pockets of the outline colour floating a sea of yellow.

What is the purpose of the crazy ant line drawing?

[folibis]

уеs, result of QPainterPath::simplified() looks a bit different. but it is ok for me.
I make a program for shape file visualization. 10 layers, part of them have about 10000 shapes. so it have to be drawn as fast as possible.