I need to display a chart that can be very large, for example the image resolution could be 100 000 x 1000. However, it seems like I am limited to 32768 x 32768 by the QImage.
I can't reasonably redraw directly the chart at every paintEvent so I need to store it into a QImage (it could be a QPixmap that won't change anything). But then, it doesn't fit.
My first idea was:

Create a list of QImage
Plot on the various QImage
Redraw using the good QImages.

The first and last points have been done quite easily. But the second point is more complex. I'm quite confident that my approach would work but it requires to overload the basic paint methods (draw rectangle, circles, etc.) in order to be able to paint on multiple images.
So, before going any further, I would like to know what could be the other options.
You can use the Qt Graphics View Framework. Create a QGraphicsView and a QGraphicsScene for it. Add items using QGraphicsScene::addPixmap (that returns QGraphicsPixmapItem which is derived from QGraphicsItem) and adjust their positions using QGraphicsItem::setPos. QGraphicsView will effectively draw your scene and handle scrolling and zooming if necessary.
Draw an image too big to fit into a QImage