WheelEvent reimplementation of a class derived from QGraphicsView

[Sergex]

Hello,

I reimplemented the wheelEvent in my graphicsView class to be able to zoom in and zoom out smoothly in width of an image. At first the implementation was:

float exp  = (event->delta() / 240.0);
float factor = powf(3/4, exp);
scale(factor, 1.0);

float exp  = (event->delta() / 240.0);
float factor = powf(3/4, exp);
scale(factor, 1.0);

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This works great, except that I don't want to be able to zoom out too much that the image starts being smaller than the widget that contains it. I want the container widget rectangle to be the minimum width of the image.

For this I tried using transforms the following way:
In the wheel event I did this instead:
(item is my GraphicsItem object)

//just changed the line : scale(factor, 1.0) to:
item->setScale(factor);

//just changed the line : scale(factor, 1.0) to:
item->setScale(factor);

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and in my class derived from QGraphicsItem I added to methods:

void setScale(float factor);
void updateTransform();
 
//In their implementations I did: 
 
void mygraphicsItem::setScale(float factor)
{
m_factor = factor;
updateTransform();
}
 
void mygraphicsItem::updateTransform()
{
QTransform transform;
 transform.scale(m_factor, 1.0);
 setTransform(transform);
}

void setScale(float factor);
void updateTransform();

//In their implementations I did: 

void mygraphicsItem::setScale(float factor)
{
m_factor = factor;
updateTransform();
}

void mygraphicsItem::updateTransform()
{
QTransform transform;
 transform.scale(m_factor, 1.0);
 setTransform(transform);
}

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Now the part to prevent and control the zooming is not implemented yet since I am jsut testing this, but shouldn't something like this do the same thing as before when I was scaling the view instead of the item?

Am I remotely on the right track to accomplish what I want? How can this be done?

Thanks!

This last way does nothing like before,

[wysota]

Isn't setScale an already existing non-virtual method of QGraphicsItem?

[Sergex]

Isn't setScale an already existing non-virtual method of QGraphicsItem?

Ok yes, it is. So I changed it to set setItemScale. Its not my point to overload the already existent function.

[wysota]

It wouldn't work anyway, would it?

[Sergex]

If it did I wouldn't be posting in this forum now would I? Why bother with the useless rhetorical questions..

[wysota]

I mean trying to override the method wouldn't work. Your method simply could never be called.

I admit I have no idea what you are trying to do, it seems obvious to try it this way:

void Cls::wheelEvent(...) {
  qreal sc = item->scale();
  if(wheel goes up) sc+= 0.1; // or whatever
  else if(wheel goes down) sc -= 0.1;
  item->setScale(qBound(0.1, sc, 2.0));
}

void Cls::wheelEvent(...) {
  qreal sc = item->scale();
  if(wheel goes up) sc+= 0.1; // or whatever
  else if(wheel goes down) sc -= 0.1;
  item->setScale(qBound(0.1, sc, 2.0));
}

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