(QtBeginner) GraphicScene update() and repaint() SLOW performance

[Qt_Bg]

This post is deleted!

[Asperamanca]

What number of points do you have?

Some performance hints:
-) Do not use pens with a width other than 1. They are slow (known issue, won't be fixed anymore)
-) Do not draw the line segments one by one, but use drawPolyline instead

You might also want to take a look at how QWT does it.

[Qt_Bg]

@Asperamanca said:

number of points do you

ECG wave line has total 2000 points.
I started seeing this slow performance issue after adding a precursor vertical line in front of ECG wave.
Without the precursor line I did not see any slow down issue.

/Coverup precursor line
                painter->setPen(QPen(QColor(0,0,0,255)));
                painter->drawLine(QLineF(left_foregrnd + p0.x(),(int)rect.top(), left_foregrnd + p0.x(), (int)rect.bottom()));
                //Draw precursor guide line
                painter->setPen(QPen(QColor(0,190,89,145)));
                painter->drawLine(QLineF(left_foregrnd + p1.x(),(int)rect.top(), left_foregrnd + p1.x(), (int)rect.bottom()));
#endif