How to change the content's position in viewport?

[aaron]

Hi all,
I am a new Qt programmer, and now, I have a question need your help.

I want to zoom in the picture which showing in QGraphicsView. The work flow like below:
press down right button and get the mouse position(mZoomStartPoint) -> move the mouse and draw a rectangle
via QRubberBand class ->release the mouse and get the mouse position(to_point).
and then, scale the picture and show the items which are covered by the rectangle center on the viewport.
the Qt code are:

//MyGraphicsView inherites QGraphicsView

void MyGraphicsView::mousePressEvent(QMouseEvent *e)
{
  if(e->button() == Qt::RightButton)
  {
   mpMouseEvent = e;
   setZoomBeginPosition();
  }
}
 
void MyGraphicsView::mouseMoveEvent(QMouseEvent *e)
{
  if(e->button() == Qt::RightButton)
  {
   setZoomMoveTo();
  }
} 
 
 
void MyGraphicsView::mouseReleaseEvent(QMouseEvent *e)
{
  if(e->button() == Qt::RightButton)
  {
     setZoomFinish();
  }
} 
 
void MyGraphicsView::setZoomBeginPosition()
{
  mZoomStartPoint = mpMouseEvent->pos();
  mpRubberBand->setGeometry(QRect(mZoomStartPoint, QSize()));
  mpRubberBand->show();
}
 
void MyGraphicsView::setZoomMoveTo()
{
  QPoint to_point = mpMouseEvent->pos();
  if(mpRubberBand)
     mpRubberBand->setGeometry(QRect(mZoomStartPoint, to_point).mormalized());
}
 
void MyGraphicsView::setZoomFinish()
{
  Qpoint to_point = mpMouseEvent->pos();
  int left_x = to_point.x()<mZoomStartPoint.x() ? to_point.x() : mZoomStartPoint.x();
  int right_x = to_point.x()>mZoomStartPoint.x() ? to_point.x() : mZoomStartPoint.x();
  int top_y  = to_point.y()<mZoomStartPoint.y() ? to_point.y() : mZoomStartPoint.y();
  int bottom_y  = to_point.y()<mZoomStartPoint.y() ? to_point.y() : mZoomStartPoint.y();
 
  if(abs(left_x - right_x)<10 || abs(top_y - bottom_y) < 10)
    return;
 
  float x_scale = (viewport()->width()) / (right_x - left_x);
  float y_scale = (viewport()->height()) / (bottom_y - top_y);
  float scale = x_scale < y_scale ? x_scale : y_scale;
  QMatrix m = matrix(); 
  m.scale(scale);
  setMatrix(m);
}

void MyGraphicsView::mousePressEvent(QMouseEvent *e)
{
  if(e->button() == Qt::RightButton)
  {
   mpMouseEvent = e;
   setZoomBeginPosition();
  }
}

void MyGraphicsView::mouseMoveEvent(QMouseEvent *e)
{
  if(e->button() == Qt::RightButton)
  {
   setZoomMoveTo();
  }
} 


void MyGraphicsView::mouseReleaseEvent(QMouseEvent *e)
{
  if(e->button() == Qt::RightButton)
  {
     setZoomFinish();
  }
} 

void MyGraphicsView::setZoomBeginPosition()
{
  mZoomStartPoint = mpMouseEvent->pos();
  mpRubberBand->setGeometry(QRect(mZoomStartPoint, QSize()));
  mpRubberBand->show();
}
 
void MyGraphicsView::setZoomMoveTo()
{
  QPoint to_point = mpMouseEvent->pos();
  if(mpRubberBand)
     mpRubberBand->setGeometry(QRect(mZoomStartPoint, to_point).mormalized());
}

void MyGraphicsView::setZoomFinish()
{
  Qpoint to_point = mpMouseEvent->pos();
  int left_x = to_point.x()<mZoomStartPoint.x() ? to_point.x() : mZoomStartPoint.x();
  int right_x = to_point.x()>mZoomStartPoint.x() ? to_point.x() : mZoomStartPoint.x();
  int top_y  = to_point.y()<mZoomStartPoint.y() ? to_point.y() : mZoomStartPoint.y();
  int bottom_y  = to_point.y()<mZoomStartPoint.y() ? to_point.y() : mZoomStartPoint.y();
  
  if(abs(left_x - right_x)<10 || abs(top_y - bottom_y) < 10)
    return;

  float x_scale = (viewport()->width()) / (right_x - left_x);
  float y_scale = (viewport()->height()) / (bottom_y - top_y);
  float scale = x_scale < y_scale ? x_scale : y_scale;
  QMatrix m = matrix(); 
  m.scale(scale);
  setMatrix(m);
}

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When I test, the items which covered by Rectangle can not show center on viewport , I must srcoll the slider to show the items
and zoom fit the picture, then test again , the items will be show.

So, would you like help me ? Thanks a lot !