how would you drawPolyLine that has missing segments

[vonCZ]

I have a QVector, "wellData", of QPoints that I render on a subclassed QWidget like so:

void SkiggleLinePanel::paintEvent(QPaintEvent *e)
{
 
  //  QVector<QPoint>  wellData;
 
  QPainter painter(this);
 
  painter.drawPolyline(wellData.data(), wellData.size());
 
}

void SkiggleLinePanel::paintEvent(QPaintEvent *e)
{

  //  QVector<QPoint>  wellData;

  QPainter painter(this);

  painter.drawPolyline(wellData.data(), wellData.size());

}

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This works as expected. Suppose, however, that I have 7 QPoints with values like so:

0 1
2 2
1 3
3 -9
7 5
6 6
2 3

These are X and Y values, *except* -9 is actually a NULL data value, and this particular x,y coordinate pair should be thrown out... So instead of one longish line of 7 points, I would want 2 shorter lines of 3 points each. How to do this?

One obvious fix: use QVector's members to find -9, then split it into 2 QVectors, and draw both of these. BUT: the actual problem involves a very long Polyline consisting of thousands of QPoints with many NULL values scattered throughout... so doing this would be very cumbersome. Are there other options here?

[wysota]

QPainter::drawPolyline() takes an array of points and the number of points to draw so you can obtain what you want using this simple loop:

QVector<QPoint> points;
// fillWithData(points);
//...
int start = 0;
for(int i=0;i<points.size();i++){
  QPoint pt = points.at(i);
  if(pt.x()==-9 || pt.y()==-9){
    // draw from start to the current point
    if(start!=i){
      painter.drawPolyline(points.constData()+start, i-start);
    }
    start = i;
  }
}
if(start!=points.size()-1){
  painter.drawPolyline(points.constData()+start, points.size()-1-start);
}

QVector<QPoint> points;
// fillWithData(points);
//...
int start = 0;
for(int i=0;i<points.size();i++){
  QPoint pt = points.at(i);
  if(pt.x()==-9 || pt.y()==-9){
    // draw from start to the current point
    if(start!=i){
      painter.drawPolyline(points.constData()+start, i-start);
    }
    start = i;
  }
}
if(start!=points.size()-1){
  painter.drawPolyline(points.constData()+start, points.size()-1-start);
}

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