replot() performance

[raghvendramisra]

Thanx a lot spitfire,
its great help
The vertical marker is now slaved to the x axis. And as suggested by you i am able to add a circle , the position of which can be varied using x and y values.
However there is some problem regarding the size of the circle. The maximum size of the circle can be equal to the width of the Vertical line and to make circle noticeable i have to increase the size of the vertical bar. As a result the vertical bar becomes wider and hides the significant portion of the graph. when i try to just increase the size of the circle without increasing the size of vertical bar, the circle is clipped and only a portion of it is visible on the bar.
I need to display a thin vertical bar with a noticeable circle as shown in your demo pic.
Kindly suggest how to achieve this.

Regards
Raghav

[Spitfire]

Look at paintEvent() in my example.
You get thin line by drawing a line from top to bottom (not by setting a background or anything).
Then you draw a circle using full width of the widget.
This way you can adjust size of the circle by changing width of the widget.

void    LineMarker::paintEvent( QPaintEvent* e )
{
    int middle = this->width()/2;
    QPainter p( this );
    p.setBrush( Qt::NoBrush );
    p.setPen( this->palette().foreground().color() ); // change pen width here if you want wider line
 
    p.drawLine( middle, 0, middle, this->height() ); // here you draw the thin lne using default pen (about 1px wide)
 
    p.setBrush( Qt::white );
    p.drawEllipse( QPoint( middle, this->elipsePosY ), middle-1, middle-1 ); // here you draw the circle with radius = width/2
}

void    LineMarker::paintEvent( QPaintEvent* e )
{
    int middle = this->width()/2;
    QPainter p( this );
    p.setBrush( Qt::NoBrush );
    p.setPen( this->palette().foreground().color() ); // change pen width here if you want wider line

    p.drawLine( middle, 0, middle, this->height() ); // here you draw the thin lne using default pen (about 1px wide)

    p.setBrush( Qt::white );
    p.drawEllipse( QPoint( middle, this->elipsePosY ), middle-1, middle-1 ); // here you draw the circle with radius = width/2
}

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[raghvendramisra]

Thanx for the help.
It worked

Raghav