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());

}

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);
}