refreshtest example: newbie understanding problems

[emigrand]

Hello everyone - thx for reading!

I am working on a plot for an ad-converter. Because I'm new to C++, Qt and Qwt, I am currently studying the refreshtest example to get a clue of how to implement the plot. I think I get most of the code, but the following is not clear to me:

When and by what are these functions called:

QPointF CircularBuffer::sample(size_t i) const
{
    const int size = d_values.size();
 
    int index = d_startIndex + i;
    if ( index >= size )
        index -= size; 
 
    const double x = i * d_step - d_offset - d_interval;
    const double y = d_values.data()[index];
 
    return QPointF(x, y);
}
 
QRectF CircularBuffer::boundingRect() const
{
    return QRectF(-1.0, -d_interval, 2.0, d_interval);
}

QPointF CircularBuffer::sample(size_t i) const
{
    const int size = d_values.size();
    
    int index = d_startIndex + i;
    if ( index >= size )
        index -= size; 

    const double x = i * d_step - d_offset - d_interval;
    const double y = d_values.data()[index];

    return QPointF(x, y);
}

QRectF CircularBuffer::boundingRect() const
{
    return QRectF(-1.0, -d_interval, 2.0, d_interval);
}

To copy to clipboard, switch view to plain text mode 

Since this is the Qwt forum, I desisted from posting the whole code of the example. I hope thats fine.


Looking forward for your help!
Emi

[Uwe]

Like the name of the class indicates this is a circular buffer with fixed samples, where the start index gets modified by time. It is only for the example - nothing you need to spend your time with.

All you you should have understood is that you can assign arrays of points to a curve or implement a bridge ( like CircularBuffer ) that reads the points from however you need to store your points.

Uwe

[emigrand]

Thanks Uwe!

Like the name of the class indicates this is a circular buffer with fixed samples, where the start index gets modified by time. It is only for the example - nothing you need to spend your time with.

Ok, I think I got this roughly. But for a general understanding it would be nice to know how and when these functions are called. I can't find anything in the code which triggers CircularBuffer::sample(). But if I add qDebug("bla") to the function, I see it is called regularly. Maybe this is basic knowledge, which I didn't stumble over yet!?

I know this might be a question for the newbie forum, but in my first thread about Qwt I was asked to post here next time.

Thank you for your help,
Emi