How do I find out which widgets/canvas items are visible?

[jacek]

I call QCanvasItem.update(). Well, it is a subclass where I implement the drawing of the item. Whenever a data even occurs in my system I have to go through a lengthy formatting procedure and prepare the output, then I call update() to get the data rendered.

QCanvasItem::update() only marks canvas chunks as modified. IMO it shouldn't trigger any repainting (the docs say something different, so I might have missed something when I was reading the sources).

BTW. You can try tuning the QCanvas chunk size. Also make sure that your item reports proper bounding rectangle.

[Tommytrojan]

QCanvasItem::update() only marks canvas chunks as modified. IMO it shouldn't trigger any repainting (the docs say something different, so I might have missed something when I was reading the sources).

BTW. You can try tuning the QCanvas chunk size. Also make sure that your item reports proper bounding rectangle.

Well, the item gets updated properly, so I assume that the bounding rectangle and everything else is okay. The problem is that it does get updated every time! I would like it to invoke my draw() function only when it actually is visible. However, I calls my draw() function even when it is obscured...

T

[jacek]

Well, the item gets updated properly, so I assume that the bounding rectangle and everything else is okay.

Yes, but the bigger bounding rectangle is, the more likely update is to occur.

The problem is that it does get updated every time! [...]However, I calls my draw() function even when it is obscured...

It looks like Qt doesn't know that a part of a window is hidden under another one.

In case somebody wants to research this subject further, I've attached a little program I wrote to test few ideas.