How to get points drawn by strokePath from outline of QPainterPath

[Uwe]

This is (3 steps - tricky) way, but gives you 100% accuracy of points drawn by QPainter.

To be honest I didn't get the point of this all - QPainterPath has a public API for reading all coordinates ?

QPainterPath polygonPath; 
polygonPath.moveTo(10.0, 80.0);
...
 
for ( int i = 0; i < polygonPath.elementCount(); i++ )
{
    const auto el = polygonPath.elementAt( i );
    switch( el.type() )
    {
        case QPainterPath::MoveToElement:
           ....
           break;
        ....
    };
}

QPainterPath polygonPath; 
polygonPath.moveTo(10.0, 80.0);
...

for ( int i = 0; i < polygonPath.elementCount(); i++ )
{
    const auto el = polygonPath.elementAt( i );
    switch( el.type() )
    {
        case QPainterPath::MoveToElement:
           ....
           break;
        ....
    };
}

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In case you really need a record/replay paint device using QPicture would make more sense as no file IO would be involved. Of course you could also write your own type of paint device for recording QPainter commands like being done f.e in http://qwt.sourceforge.net/class_qwt...nt_device.html.

Uwe

[userman]

To be honest I didn't get the point of this all - QPainterPath has a public API for reading all coordinates ?

QPainterPath polygonPath; 
polygonPath.moveTo(10.0, 80.0);
...
 
for ( int i = 0; i < polygonPath.elementCount(); i++ )
{
    const auto el = polygonPath.elementAt( i );
    switch( el.type() )
    {
        case QPainterPath::MoveToElement:
           ....
           break;
        ....
    };
}

QPainterPath polygonPath; 
polygonPath.moveTo(10.0, 80.0);
...

for ( int i = 0; i < polygonPath.elementCount(); i++ )
{
    const auto el = polygonPath.elementAt( i );
    switch( el.type() )
    {
        case QPainterPath::MoveToElement:
           ....
           break;
        ....
    };
}

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In case you really need a record/replay paint device using QPicture would make more sense as no file IO would be involved. Of course you could also write your own type of paint device for recording QPainter commands like being done f.e in http://qwt.sourceforge.net/class_qwt...nt_device.html.

Uwe

Uwe, you didn't get the point of this all... because you did not read my first post carefully. Please view attached image in first post.
qt-quest1.jpg
Yes you can read those points this way

polygonPath.elementAt( i );

polygonPath.elementAt( i );

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But it gives you only the middle points of the QPen, marked as green/yellow dash line on my attached image.
In my example i need to find points marked as black line (on attached image)
If you known solution how to do this, please share this info.

Thanks d_stranz yes I can use QIODevice like this:

QBuffer buffer;
buffer.open(QBuffer::ReadWrite);
QSvgGenerator generator;
generator.setOutputDevice(&buffer);
... 
buffer.seek(0);
QString s(buffer.readAll());
qInfo() << s;

QBuffer buffer;
buffer.open(QBuffer::ReadWrite);
QSvgGenerator generator;
generator.setOutputDevice(&buffer);
... 
buffer.seek(0);
QString s(buffer.readAll());
qInfo() << s;

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(do not create physical file - but i did not it for illustrate what is going on. For my purpose, I needed those points in XML anyway, but use setOutputDevice for speed up process is a very good idea)

In example form attached image - has to be created stroke path from red Curve, and read stroke path coordinates from SVG to find those points of black path.
Or there is better solution Uwe?

[Uwe]

Uwe, you didn't get the point of this all... because you did not read my first post carefully.

Well, there is QPainterPathStroker that is also internally used to create the QPainterPath that gets finally rendered.
So what you need to do is to set up the stroker with the attributes of your pen and then the strokedPath can be read like in my previous posting.

Thought you were talking about the strokedPath in your initial posting as you called it like that.

Uwe

[userman]

So the (other) final solution is:

Draw along outline points of shape:
qt-quest1.1.jpg

QPainterPath path(QPointF(80, 320));
path.lineTo(QPointF(240,90));
path.lineTo(QPointF(330,240));
path.lineTo(QPointF(620,180));
path.lineTo(QPointF(730,110));
 
QPainterPathStroker stroker;
stroker.setCapStyle(Qt::RoundCap);
stroker.setJoinStyle(Qt::RoundJoin);
stroker.setWidth(100);
 
QPainterPath strokePath = stroker.createStroke(path).simplified();
 
for (int i = 0; i < strokePath.elementCount()-1; i++)
{
  QPainterPath::Element p1 = strokePath.elementAt(i);
  QPainterPath::Element p2 = strokePath.elementAt(i+1);
  painter->setPen(QPen(i % 2 == 0 ? Qt::red : Qt::green, 1));
  painter->drawLine(QPointF(p1.x, p1.y), QPointF(p2.x, p2.y));
}

QPainterPath path(QPointF(80, 320));
path.lineTo(QPointF(240,90));
path.lineTo(QPointF(330,240));
path.lineTo(QPointF(620,180));
path.lineTo(QPointF(730,110));

QPainterPathStroker stroker;
stroker.setCapStyle(Qt::RoundCap);
stroker.setJoinStyle(Qt::RoundJoin);
stroker.setWidth(100);

QPainterPath strokePath = stroker.createStroke(path).simplified();

for (int i = 0; i < strokePath.elementCount()-1; i++)
{
  QPainterPath::Element p1 = strokePath.elementAt(i);
  QPainterPath::Element p2 = strokePath.elementAt(i+1);
  painter->setPen(QPen(i % 2 == 0 ? Qt::red : Qt::green, 1));
  painter->drawLine(QPointF(p1.x, p1.y), QPointF(p2.x, p2.y));
}

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Solved.