QScrollarea events transferring to scrollbar

[babu198649]

hi
i have subclassed QScrollArea to receive mouse move events .
now when i move the mouse the scrollbars should be moved accordingly(up and down movements for vertical scrollbar and left and right movements for horizontal scrollbar).

how can i transfer the mouse move event of scrollarea to scrollbar

[wysota]

i have subclassed QScrollArea to receive mouse move events .
now when i move the mouse the scrollbars should be moved accordingly(up and down movements for vertical scrollbar and left and right movements for horizontal scrollbar).

how can i transfer the mouse move event of scrollarea to scrollbar

Why not use QScrollBar::setValue() to set the value of the scrollbar?

[babu198649]

yes i have tried it but it makes exection slower.

i have tried like this

void iv_scrollarea::mouseMoveEvent ( QMouseEvent * event )
{
	if(this->underMouse())
	{
	if(old_position.x() > event->pos().x())//old position is qpoint it remembers last position
	  this->horizontalScrollBar()->setValue(this->horizontalScrollBar()->value() + 1);
 
	if(old_position.x() < event->pos().x())
	  this->horizontalScrollBar()->setValue(this->horizontalScrollBar()->value() - 1);
 
	if(old_position.y() > event->pos().y())
	  this->verticalScrollBar()->setValue(this->verticalScrollBar()->value() + 1);
 
	if(old_position.y() < event->pos().y())
	  this->verticalScrollBar()->setValue(this->verticalScrollBar()->value() - 1);
	}
       old_position = event->pos();
}

void iv_scrollarea::mouseMoveEvent ( QMouseEvent * event )
{
	if(this->underMouse())
	{
	if(old_position.x() > event->pos().x())//old position is qpoint it remembers last position
	  this->horizontalScrollBar()->setValue(this->horizontalScrollBar()->value() + 1);
			
	if(old_position.x() < event->pos().x())
	  this->horizontalScrollBar()->setValue(this->horizontalScrollBar()->value() - 1);
			
	if(old_position.y() > event->pos().y())
	  this->verticalScrollBar()->setValue(this->verticalScrollBar()->value() + 1);
			
	if(old_position.y() < event->pos().y())
	  this->verticalScrollBar()->setValue(this->verticalScrollBar()->value() - 1);
	}
       old_position = event->pos();
}

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the above code takes long movement of the mouse to move the label inside the QScrollArea. because at every pixel moved the movement of label does not happen

and when i set values with higher than setValue(1) (i.e. this->verticalScrollBar()->setValue(this->verticalScrollBar()->value() - 5))

the flickering occurs


when i use the move() function of label inside scrollarea mouse move event it works fine but scrollbars are not updated

[wysota]

Ok, what effect are you trying to achieve anyway? Why do you add "1" instead of computing the actual movement?

[babu198649]

Ok, what effect are you trying to achieve anyway?

i want to move the qlabel inside the qscrollarea using mouse cursor (i.e. click and move the label) simultaneously the scrollbars should get updated.

[wysota]

Doesn't something like this work?

#include <QScrollArea>
#include <QLabel>
#include <QApplication>
 
class ScrollArea : public QScrollArea {
public:
  ScrollArea(const QString &path) : QScrollArea(0){
    QLabel *l = new QLabel(this);
    setWidget(l);
    setWidgetResizable(true);
    l->setPixmap(QPixmap(path));
  }
};
 
 
int main(int argc, char **argv){
  QApplication app(argc, argv);
  ScrollArea sa(argv[1]);
  sa.show();
  return app.exec();
}

#include <QScrollArea>
#include <QLabel>
#include <QApplication>

class ScrollArea : public QScrollArea {
public:
  ScrollArea(const QString &path) : QScrollArea(0){
    QLabel *l = new QLabel(this);
    setWidget(l);
    setWidgetResizable(true);
    l->setPixmap(QPixmap(path));
  }
};


int main(int argc, char **argv){
  QApplication app(argc, argv);
  ScrollArea sa(argv[1]);
  sa.show();
  return app.exec();
}

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The scrolling works for me out of the box.

[babu198649]

the problem is not with scrolling
when i move the qlabel with the mouse(clicked and move ) the label moves a distance with respect to the distance moved by the mouse .now the scrollbar should update this movement of the label.

QLabel *l = new QLabel(this);
setWidget(l);

is this keyword nessary

[jpn]

Why don't you use built-in components, QMdiArea or QGraphicsView (depending on your needs) as already suggested in another thread?

[babu198649]

hi
i have found in the documentation that the QGraphicsView is for maintaining large number of items . but i have only one label so i thought it will not suit.

and QMdiArea class documentation says

The QMdiArea widget provides an area in which MDI windows are displayed.

but i dont have more than one window and also i need time to know what MDI windows are . so i thought that i can do these things with qscrollarea itself.

do u think the problem can not be solved with QScrollarea

[wysota]

You should really use QMdiArea or QGraphicsView as suggested, but if you insist on using the scroll area directly then this works for me:

#include <QScrollArea>
#include <QLabel>
#include <QApplication>
#include <QMouseEvent>
#include <QScrollBar>
 
 
class ScrollArea : public QScrollArea {
public:
  ScrollArea(const QString &path) : QScrollArea(0){
    l = new QLabel(this);
    setWidget(l);
    setWidgetResizable(true);
    l->setPixmap(QPixmap(path));
    l->installEventFilter(this);
  }
  bool eventFilter(QObject *o, QEvent *e){
    if(o!=l)
      return QScrollArea::eventFilter(o,e);
    if(e->type()==QEvent::MouseButtonPress){
      m_prev = ((QMouseEvent*)e)->pos();
      return true;
    }
    if(e->type()==QEvent::MouseMove){
      QPoint pt = ((QMouseEvent*)e)->pos();
      QPoint diff = pt-m_prev;
      m_prev = pt;
      horizontalScrollBar()->setValue(horizontalScrollBar()->value()+diff.x());
      verticalScrollBar()->setValue(verticalScrollBar()->value()+diff.y());
      return true;
    }
    return QScrollArea::eventFilter(o,e);
  }
protected:
  QLabel *l;
  QPoint m_prev;
};
 
 
int main(int argc, char **argv){
  QApplication app(argc, argv);
  ScrollArea sa(argv[1]);
  sa.show();
  return app.exec();
}

#include <QScrollArea>
#include <QLabel>
#include <QApplication>
#include <QMouseEvent>
#include <QScrollBar>


class ScrollArea : public QScrollArea {
public:
  ScrollArea(const QString &path) : QScrollArea(0){
    l = new QLabel(this);
    setWidget(l);
    setWidgetResizable(true);
    l->setPixmap(QPixmap(path));
    l->installEventFilter(this);
  }
  bool eventFilter(QObject *o, QEvent *e){
    if(o!=l)
      return QScrollArea::eventFilter(o,e);
    if(e->type()==QEvent::MouseButtonPress){
      m_prev = ((QMouseEvent*)e)->pos();
      return true;
    }
    if(e->type()==QEvent::MouseMove){
      QPoint pt = ((QMouseEvent*)e)->pos();
      QPoint diff = pt-m_prev;
      m_prev = pt;
      horizontalScrollBar()->setValue(horizontalScrollBar()->value()+diff.x());
      verticalScrollBar()->setValue(verticalScrollBar()->value()+diff.y());
      return true;
    }
    return QScrollArea::eventFilter(o,e);
  }
protected:
  QLabel *l;
  QPoint m_prev;
};


int main(int argc, char **argv){
  QApplication app(argc, argv);
  ScrollArea sa(argv[1]);
  sa.show();
  return app.exec();
}

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[babu198649]

Thank u very much wysota
it really works great .
thanks for pain taking job of coding entirely in a short perid for me

[wysota]

You would have saved me the pain if you used the right component for the job in the first place.

[babu198649]

yes
but i followed the image viewer example

[wysota]

I advise you to follow JPN's hints next time. Your use case seemed a perfect candidate for QGraphicsView, especially if you intend to do something more with it (like introduce zooming).

[babu198649]

sure, thank u

[Sirganor]

You should really use QMdiArea or QGraphicsView as suggested, but if you insist on using the scroll area directly then this works for me:

#include <QScrollArea>
#include <QLabel>
#include <QApplication>
#include <QMouseEvent>
#include <QScrollBar>
 
 
class ScrollArea : public QScrollArea {
public:
  ScrollArea(const QString &path) : QScrollArea(0){
    l = new QLabel(this);
    setWidget(l);
    setWidgetResizable(true);
    l->setPixmap(QPixmap(path));
    l->installEventFilter(this);
  }
  bool eventFilter(QObject *o, QEvent *e){
    if(o!=l)
      return QScrollArea::eventFilter(o,e);
    if(e->type()==QEvent::MouseButtonPress){
      m_prev = ((QMouseEvent*)e)->pos();
      return true;
    }
    if(e->type()==QEvent::MouseMove){
      QPoint pt = ((QMouseEvent*)e)->pos();
      QPoint diff = pt-m_prev;
      m_prev = pt;
      horizontalScrollBar()->setValue(horizontalScrollBar()->value()+diff.x());
      verticalScrollBar()->setValue(verticalScrollBar()->value()+diff.y());
      return true;
    }
    return QScrollArea::eventFilter(o,e);
  }
protected:
  QLabel *l;
  QPoint m_prev;
};
 
 
int main(int argc, char **argv){
  QApplication app(argc, argv);
  ScrollArea sa(argv[1]);
  sa.show();
  return app.exec();
}

#include <QScrollArea>
#include <QLabel>
#include <QApplication>
#include <QMouseEvent>
#include <QScrollBar>


class ScrollArea : public QScrollArea {
public:
  ScrollArea(const QString &path) : QScrollArea(0){
    l = new QLabel(this);
    setWidget(l);
    setWidgetResizable(true);
    l->setPixmap(QPixmap(path));
    l->installEventFilter(this);
  }
  bool eventFilter(QObject *o, QEvent *e){
    if(o!=l)
      return QScrollArea::eventFilter(o,e);
    if(e->type()==QEvent::MouseButtonPress){
      m_prev = ((QMouseEvent*)e)->pos();
      return true;
    }
    if(e->type()==QEvent::MouseMove){
      QPoint pt = ((QMouseEvent*)e)->pos();
      QPoint diff = pt-m_prev;
      m_prev = pt;
      horizontalScrollBar()->setValue(horizontalScrollBar()->value()+diff.x());
      verticalScrollBar()->setValue(verticalScrollBar()->value()+diff.y());
      return true;
    }
    return QScrollArea::eventFilter(o,e);
  }
protected:
  QLabel *l;
  QPoint m_prev;
};


int main(int argc, char **argv){
  QApplication app(argc, argv);
  ScrollArea sa(argv[1]);
  sa.show();
  return app.exec();
}

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It makes something wrong when you drag it more than one pixel in one direction. Is accumulative. I got one solution for it:

#include <QScrollArea>
#include <QLabel>
#include <QApplication>
#include <QMouseEvent>
#include <QScrollBar>
#include<QDebug>
 
class ScrollArea : public QScrollArea {
public:
ScrollArea() : QScrollArea()
{
    this->n=3;
    this->prev_diff.setX(0);
    this->prev_diff.setY(0);
    l = new QLabel(this);
    QImage imagen("C:/donostia.jpg");
    l->setPixmap(QPixmap::fromImage(imagen));
    setWidget(l);
    setWidgetResizable(true);
    //l->setPixmap(QPixmap(path));
    l->installEventFilter(this);
}
bool eventFilter(QObject *o, QEvent *e)
{
    if(o!=l)
        return QScrollArea::eventFilter(o,e);
    if(e->type()==QEvent::MouseButtonPress)
    {
        m_prev = ((QMouseEvent*)e)->pos();
        this->prev_diff.setX(0);
        this->prev_diff.setY(0);
        return true;
    }
    if(e->type()==QEvent::MouseMove)
    {
        QPoint pt = ((QMouseEvent*)e)->pos();
        this->diff = pt-m_prev-prev_diff*n;
        m_prev = pt;
        horizontalScrollBar()->setValue(horizontalScrollBar()->value()+diff.x()*n);
        verticalScrollBar()->setValue(verticalScrollBar()->value()+diff.y()*n);
        qDebug()<<"("+QString::number(diff.x())+","+QString::number(diff.y())+")";
        this->prev_diff=diff;
        return true;
    }
    return QScrollArea::eventFilter(o,e);
}
protected:
    QLabel *l;
    QPoint m_prev;
    QPoint diff;
    QPoint prev_diff;
    int n;
};
 
 
int main(int argc, char **argv)
{
    QApplication app(argc, argv);
    ScrollArea sa;
    sa.show();
    return app.exec();
}

#include <QScrollArea>
#include <QLabel>
#include <QApplication>
#include <QMouseEvent>
#include <QScrollBar>
#include<QDebug>

class ScrollArea : public QScrollArea {
public:
ScrollArea() : QScrollArea()
{
    this->n=3;
    this->prev_diff.setX(0);
    this->prev_diff.setY(0);
    l = new QLabel(this);
    QImage imagen("C:/donostia.jpg");
    l->setPixmap(QPixmap::fromImage(imagen));
    setWidget(l);
    setWidgetResizable(true);
    //l->setPixmap(QPixmap(path));
    l->installEventFilter(this);
}
bool eventFilter(QObject *o, QEvent *e)
{
    if(o!=l)
        return QScrollArea::eventFilter(o,e);
    if(e->type()==QEvent::MouseButtonPress)
    {
        m_prev = ((QMouseEvent*)e)->pos();
        this->prev_diff.setX(0);
        this->prev_diff.setY(0);
        return true;
    }
    if(e->type()==QEvent::MouseMove)
    {
        QPoint pt = ((QMouseEvent*)e)->pos();
        this->diff = pt-m_prev-prev_diff*n;
        m_prev = pt;
        horizontalScrollBar()->setValue(horizontalScrollBar()->value()+diff.x()*n);
        verticalScrollBar()->setValue(verticalScrollBar()->value()+diff.y()*n);
        qDebug()<<"("+QString::number(diff.x())+","+QString::number(diff.y())+")";
        this->prev_diff=diff;
        return true;
    }
    return QScrollArea::eventFilter(o,e);
}
protected:
    QLabel *l;
    QPoint m_prev;
    QPoint diff;
    QPoint prev_diff;
    int n;
};


int main(int argc, char **argv)
{
    QApplication app(argc, argv);
    ScrollArea sa;
    sa.show();
    return app.exec();
}

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