Keep QGraphicsSimpleTextItem centered when zooming - c++

Question

I would like to create a QGraphicsRectItem and display its name with a QGraphicsSimpleTextItem. I want the size of the text to be unaffected by the zoom. I also want the position of the text to be centered on the QGraphicsRectItem.
Here is my attempt so far :
#include <QApplication>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QGraphicsRectItem>
#include <QPen>
#include <QWheelEvent>
#include <cmath>
#include <QDebug>
class MainView : public QGraphicsView {
public:
MainView(QGraphicsScene *scene) : QGraphicsView(scene) { setBackgroundBrush(QBrush(QColor(255, 255, 255)));}
protected:
void wheelEvent(QWheelEvent *event) {
double scaleFactor = pow(2.0, event->delta() / 240.0);
scale(scaleFactor, scaleFactor);
}
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QGraphicsScene scene;
scene.setSceneRect(0, 0, 800, 800);
QGraphicsRectItem* rectItem = new QGraphicsRectItem(QRectF(0, 0, 400, 200));
rectItem->setPos(200, 200);
rectItem->setBrush(QColor(255, 0, 0));
scene.addItem(rectItem);
QGraphicsSimpleTextItem *nameItem = new QGraphicsSimpleTextItem("name", rectItem);
QFont f = nameItem->font();
f.setPointSize(12);
nameItem->setFont(f);
nameItem->setFlag(QGraphicsItem::ItemIgnoresTransformations);
nameItem->setPos(rectItem->rect().center());
MainView view(&scene);
view.show();
return a.exec();
}
Unfortunately you can see : on the capture that when I unzoom ( on the right ), the text doesn't stay inside the rectangle.
How to keep the text inside the rectangle and centered ?
Thank you.

Answer 1

I also want the position of the text to be centered on the QGraphicsRectItem
What you're seeing is correct, since you're scaling about the top left of the QGraphicsView and the text item is placed in the centre of the rectangle.
If you scaled about the centre of your QGraphicsRectItem, you'd see the text would maintain its position in the centre of the rect.
Another way of looking at this is to position the text in the top left corner of the rectangle. You'll note that when you scale here, the text will appear correct, up until it can no longer fit in the rectangle.
Continue scaling and you'll see that the top left of the text is still in the centre, but since the text does not obey the transform, it is pushed outside
It may appear that the top left of the text is below the rectangle, but the bounding rect of the text takes accents into consideration (e.g è).
So, by having the text positioned in the centre of the rect, rather than the top left, the appearance of the text being outside the rect is exacerbated.
Once you've zoomed out so far, the transform of the rect is dealing in fractions of a point size, but the non transformed text is unaffected and so the difference between, for example, 0.6 and 0.9 of a pixel is irrelevant and will be positioned at the same pixel.
You need to consider what you're trying to achieve. Is it really necessary to zoom to that extent or can you restrict it beyond a certain point, where you won't notice this issue?