Cannot attach QScrollBar to QwtPlot

[mohini]

hello,
Background :
I have Plot a Histogram on QwtPlot using QwtPlotHistogram. then I have been able to magnify the plot in right direction only. Now as I magnify the plot I need A ScrollBar to view the zoomed data. for this I added a QScrollBar.
I am trying to attach a QScrollBar to My QwtPlot .

But I can't connect the QScrollBAr to QwtPlot.

the code which I am trying is : (this is in MyPlot 's constructor)

QScrollBar *hScrollBar = new QScrollBar(Qt::Horizontal,plot->canvas());
connect(hScrollBar,SIGNAL(sliderMoved(double)),thi s->canvas(),SLOT(horizontal_scroll(double)));

horizontal_scroll is my method as :

void MyPlot:: horizontal_scroll(double value)
{
setAxisScale(2, value, value + 105.0);
//plot->setAxisScale(0,50,20);
replot();
}

I am not getting where I am going wrong....!!

Thanx in advance...!

[Uwe]

You also have to write layout code ( moving + resizing the scrollbar ). If you want to have it on top of the plot canvas you have to implement an event filter catching resize and move events for the canvas.

Again look at the ScrollZoomer from the realtime example - it does this.

Uwe

[mohini]

thanx Uwe ..!
But, ScrollZoomer implements QWtPlotZoomer whereas I am using QwtPlotMagnifier ...
Its adding to my confusion ...!!
Can you please elaborate so that I can get it cleared ...!!

[Uwe]

Event filtering is a general Qt feature ( see QObject::installEventFilter() ).

Assuming your plot widget owns your scroll bar, then you have to do something like this:

class YourPlot: public QwtPlot
{
public:
    YourPlot( ... )
    {
         ....
         m_scrollBar = new QScrollBar( Qt::Horizontal, this );
         canvas()->installEventFilter(this);
    }
 
    virtual bool eventFilter(QObject *object, QEvent *e)
    {
        if ( object == canvas() )
        {
            if ( e->type() == QEvent::Move )
            {
                m_scrollBar->move( ... );
            }
            if ( e->type() == QEvent::Resize )
            {
                m_scrollBar->resize( ... );
            }
        }
        return QwtPlot::eventFilter( object, event );
    }
};

class YourPlot: public QwtPlot
{
public:
    YourPlot( ... )
    {
         ....
         m_scrollBar = new QScrollBar( Qt::Horizontal, this );
         canvas()->installEventFilter(this);
    }

    virtual bool eventFilter(QObject *object, QEvent *e)
    {
        if ( object == canvas() )
        {
            if ( e->type() == QEvent::Move )
            {
                m_scrollBar->move( ... );
            }
            if ( e->type() == QEvent::Resize )
            {
                m_scrollBar->resize( ... );
            }
        }
        return QwtPlot::eventFilter( object, event );
    }
};

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But of course you can put your scrollbar also everywhere else independant of the plot canvas geometry.

Uwe

[mohini]

thanx Uwe ..
I could attach the QScrollBar to my Plot...
It works fine when I first magnify and then scroll forward or backward. But, the problem is if I again magnify the plot (i.e after 1 magnification and 1 scrolling ) while scrolling back it doesn't scroll to right scale. I can recognize that the problem is due to 2 calls to setAxisScale on xBottom axis viz., one in magnifier::rescale (overloaded method) and the other call is in my horizontal_scroll method (SLOT for horizontal scrollbar...)

These two methods are :

void MyMagnifier::rescale(double factor)
{

if ( factor == 1.0 || factor == 0.0)
return;
hold=factor;
if(cnt!=-1)
{

//mag_stack[mag_cnt]=mag_stack[mag_cnt-1]+factor;
mag_stack[mag_cnt]=factor;
magnify_flag=1; // indicate that we have scrolled before magnifying
}
else
{
magnify_flag=0;
}

bool doReplot = false;
QwtPlot* plt = plot();

const bool autoReplot = plt->autoReplot();
plt->setAutoReplot(false);

//for ( int axisId = 0; axisId < QwtPlot::axisCnt; axisId++ ) // no need to scale all axes... as zooming only along X-Axis
//{

int axisId=2;
const QwtScaleDiv *scaleDiv = plt->axisScaleDiv(axisId);
if ( isAxisEnabled(axisId) && scaleDiv->isValid() )
{
plt->setAxisScale(axisId, scaleDiv->lowerBound() * factor , scaleDiv->upperBound() * factor);
doReplot = true;
}
// }

plt->setAutoReplot(autoReplot);

if ( doReplot )
{
plt->replot();
}
}


and

void TVPlot:: horizontal_scroll(int value)
{
scroll_flag=1;
hold_scroll=value;
static int prev_val=0;
const QwtScaleDiv *scaleDiv = axisScaleDiv(2);

if(value >prev_val && prev_val>=0)
{
cnt++;
stack[cnt]=value;
prev_val=value;
setAxisScale(2, scaleDiv->lowerBound() + value , scaleDiv->upperBound() + value);

}
else if(prev_val>0)
{
int temp;
if(magnify_flag==1)
{
int i =mag_cnt;
if(i >-1) // trying to correlate magnification factor with back scrolling value // NOT working
{
stack[cnt]=(int)(stack[cnt]-mag_stack[i]);
i--;
setAxisScale(2, scaleDiv->lowerBound() - stack[cnt] , scaleDiv->upperBound() - stack[cnt]);
cnt--;
}

}
else
{
setAxisScale(2, scaleDiv->lowerBound() - stack[cnt] , scaleDiv->upperBound() - stack[cnt]);
cnt--;
}
prev_val=value;
}

replot();
}

But , I am not getting how should I correlate the magnify axis scale to scroll axis scale ...
stack[] contains the scroll factor each time I scroll the plot.. I have done this so that I can scroll back by same factor... because while scrolling the scroll factor is 1,2,3,4.... (an A.P.)

Please suggest how to correlate these factors to magnification factor ..

I am not using the virtual bool eventFilter(QObject *object, QEvent *e) function ...!