Zooming image

[wysota]

I would subclass QAbstractScrollArea and implement everything as a single custom widget. Placing a QLabel in a QScrollArea will cause you problems sooner or later.

[MTK358]

The problem is that I'm using a Designer form. How would I put my own widget right in the middle of a layout?

[wysota]

How would I put my own widget right in the middle of a layout?

Use the "Promote to..." feature of Designer - put a QFrame on the form, right click the frame, choose "Promote to..." and enter your custom widget's data.

[MTK358]

The Promote feature is great! I didn't know about it.

But OK, I created a custom widget containing the scroll area, label, and zoom controls, but it still has the same issues. It just behaves very strangely and so inconsistently that I can't really even explain it.

[wysota]

I told you to subclass QAbstractScrollArea and implement the functionality from scratch, not to use a custom widget composed of a scroll area and a label. You will have to get your hands dirty here.

[MTK358]

OK, I looked but I don't understand what methods to reimplement and how to paint to the viewport.

[wysota]

OK, I looked but I don't understand what methods to reimplement and how to paint to the viewport.

Reimplement at least paintEvent() and optionally scrollContentsBy().

[MTK358]

OK, but how do I get a QPainter for the viewport widget?

[wysota]

You create it in the paint event like usual.

[MTK358]

Finally, I did it.

Anyway, it works great now, but I would really like it so that the user can scroll by dragging the mouse in the viewport. How would I do that?

[SixDegrees]

You're gradually reinventing QGraphicsView here. Just use that; you get all of the features you've brought up so far for free.

[MTK358]

You're gradually reinventing QGraphicsView here. Just use that; you get all of the features you've brought up so far for free.

I'm not very familiar with QGraphicsView but maybe...

Anyway, why didn't anyone else offer that?