QSlider Iteration Misses Sample Data on QCustomPlot

[cranberriess89]

Hi,
As you stated, I removed the check of "diff < 0,01" to handle the last slider correctly. Additionally, 0 - 1000 range setting just worked. But after 5 times zoom, when the range size decreases, data miss problem still exists with one iteration of QSlider.
I mean, when "the range size" is smaller than "the range which corresponds to one slider move", data miss problem occurs. And this statement emerges when 5-6 times zoom made. Do you have any suggestion to manage this situation ?

[d_stranz]

Do you have any suggestion to manage this situation ?

I think you need to look at the calculations you are doing. It sounds to me like you are dividing the unzoomed axis range by 100 or 1000 or whatever. If you do that, you will eventually reach the point you get to - the precision of the slider is less than the current zoom range, so there are areas that get skipped.

I don't really know how you want this zoom feature to behave so it is hard for me to suggest a solution.

[cranberriess89]

Hi again,

Lets say our record is 40 seconds.. QSlider range is 0-1000, and I set the range of slider at initialization, not dynamically. So in this case one move of slider is equal to 0,04 seconds. When a lot of zooms are made, the difference btw lower and upper range is smaller than one move size (0.04 seconds). That's why areas are skipped .. Isn't there any way of changing "area size of one qslider move" ? If the area corresponding to the one qslider move decreases, my problem will be resolved. Do you still think DoubleSlider widget is not a solution ?

Thanks in advance,
Kind Regards

[d_stranz]

So in this case one move of slider is equal to 0,04 seconds.

That's what I suspected - you are using the unzoomed (full) range of your data to set the slider increment.

Each time you zoom in (or out), you need to reset the mapping between slider value and range so that it matches the current zoomed-in range. So if the initial range is 0 - 40 seconds, and you zoom in by 2x around the center, then the new range is 10 - 30 seconds. The next step halves that again, to 15 - 25 seconds, and so on. You can probably change the slider range to something like 0 - 10 or 0 - 20 steps, so at most you can zoom in by 2^20 if each step zooms by 2x. If a 2x zoom for each step is too much, then use a smaller factor - 1.5 - but not less than 1.0 (which is no zoom at all).

[cranberriess89]

As you realized, I should update the value of one move of QSlider dynamically when zoomed. As fas as I examined, “One QSlider Move = QCustomPlot Range Size/ QSlider Maximum Width"
For every zoom, I already update the range of QCustomPlot and value of QSlider but somehow "One QSlider Move" not updated. Is this a bug of QSlider ? I traced logs but after zoom operation, one move iteration width is the same with not zoomed one ( 0.04 seconds ). Do you know the way of updating one move iteration value dynamically ?

There is a setter of QSlider, setSingleStep(int). I thought I can set it dynamically when zoomed, but it takes only integer values..

[d_stranz]

Is this a bug of QSlider ?

No, it is a bug in your logic. You need to compute the zoom factor after each step, and use that new factor to scale the plot for the next step. You do not need to change the slider range, ever. What you need to change is how your code translates the current slider value and current plot range into a new width in seconds.

You probably should post your complete code for how you are doing your zoom operation, and explain in detail what should happen to the plot each time the user moves the slider one step.

[cranberriess89]

For every zoom, xAxisChanged slot is triggered. So I set new range and values to increase the precision of QSlider, but it didn't work. When range size of QCustomPlot is smaller than one iteration width of QSlider, some areas get skipped.

View::View(QWidget *parent) :
    AbstractMainWindow(parent),
    ui(new Ui::View)
{
    precision = 1000.0;
	/*  ui->horizontalScrollBar = QSlider*/
    ui->horizontalScrollBar->setTracking(true);
    ui->horizontalScrollBar->setVisible(false);
    ui->horizontalScrollBar->setMinimum(0);
    ui->horizontalScrollBar->setMaximum(precision);
}
 
void View::horzScrollBarChanged(int value)
{
   double ratio = (double)value/(double)(ui->horizontalScrollBar->maximum());
   double val = ratio*graphmaxValue;
   qDebug()<<"horzScrollBarChanged value : " <<val << "range size:"<< plot->xAxis->range().size();
   qDebug()<<"horzScrollBarChanged range : " << plot->xAxis->range();
 
   plot->xAxis->setRange(val, plot->xAxis->range().size(), Qt::AlignCenter);
   plot->replot();
 
}
 
void View::xAxisChanged(QCPRange range)
{
    qDebug()<<"xAxisChanged : range " <<range << "range size:" <<range.size() << "range center:" << range.center();
    int value = qRound((range.center()*precision)/graphmaxValue);
 
    double currentRangeSize = range.size();
    /* initialRangeSize is set when the plot is loaded firstly */
    double ratio = currentRangeSize*1000/initialRangeSize;
    int newSliderMaximum = (ratio)*1000;
 
    ui->horizontalScrollBar->setMaximum(newSliderMaximum);
    ui->horizontalScrollBar->adjustSize();
 
    qDebug()<<"xAxisChanged horzScrollBar max: " << ui->horizontalScrollBar->maximum();
 
    int newRangeValue = (value/1000.0)*(ui->horizontalScrollBar->maximum());
    ui->horizontalScrollBar->setValue(newRangeValue);
 
}

View::View(QWidget *parent) :
    AbstractMainWindow(parent),
    ui(new Ui::View)
{
    precision = 1000.0;
	/*  ui->horizontalScrollBar = QSlider*/
    ui->horizontalScrollBar->setTracking(true);
    ui->horizontalScrollBar->setVisible(false);
    ui->horizontalScrollBar->setMinimum(0);
    ui->horizontalScrollBar->setMaximum(precision);
}

void View::horzScrollBarChanged(int value)
{
   double ratio = (double)value/(double)(ui->horizontalScrollBar->maximum());
   double val = ratio*graphmaxValue;
   qDebug()<<"horzScrollBarChanged value : " <<val << "range size:"<< plot->xAxis->range().size();
   qDebug()<<"horzScrollBarChanged range : " << plot->xAxis->range();

   plot->xAxis->setRange(val, plot->xAxis->range().size(), Qt::AlignCenter);
   plot->replot();
   
}

void View::xAxisChanged(QCPRange range)
{
    qDebug()<<"xAxisChanged : range " <<range << "range size:" <<range.size() << "range center:" << range.center();
    int value = qRound((range.center()*precision)/graphmaxValue);
	
    double currentRangeSize = range.size();
    /* initialRangeSize is set when the plot is loaded firstly */
    double ratio = currentRangeSize*1000/initialRangeSize;
    int newSliderMaximum = (ratio)*1000;

    ui->horizontalScrollBar->setMaximum(newSliderMaximum);
    ui->horizontalScrollBar->adjustSize();

    qDebug()<<"xAxisChanged horzScrollBar max: " << ui->horizontalScrollBar->maximum();
    
    int newRangeValue = (value/1000.0)*(ui->horizontalScrollBar->maximum());
    ui->horizontalScrollBar->setValue(newRangeValue);

}

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[d_stranz]

increase the precision of QSlider

You keep referring to QSlider, but your code indicates a horizontal scrollbar. Which is it?

[cranberriess89]

It is QSlider, "ui->horizontalScrollBar" is an instance of QSlider..