Custom QGraphicsItem being painted even when completely obscured

[ChristianEhrlicher]

Can't you just cache the rendered output and just paint the cached image in the paint event?

[Micah]

I don't think so... I have hundreds of images being generated on the fly every second. I put them in a QGraphicsScene with a bunch of other QGraphicsItems. The user has the ability to make some of the QGraphicsItems visible/invisible at run time, so at the time the images are generated, I don't know which will be needed and which won't be needed.

Once an image does get rendered, I cache the rendered image for any repaintings. But the normal use case is to generate new images at 60fps. I do have time to render just the "top layer" of images and keep that frame rate. But because I am also spending time rendering in paint() calls for the lower (obscured) images, I'm overrunning my frame time.

[ChristianEhrlicher]

60fps? and than hundreds of images at this rate? Then you should definitely think about your design. E.g. render the stuff in separate threads. But why such a high frame rate at all?
Did you take a look at https://doc.qt.io/qt-5/qgraphicsitem...CacheMode-enum ?

[Micah]

I'd like to avoid the call to paint() in the first place, so caching doesn't help. The high frame rate is because my application takes input from a connected camera which outputs at that rate. I turn its output into processed video.

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Added after 8 minutes:

Thanks for the suggestions though. I'll think about some other ways I can avoid putting the QGraphicsItems in the scene in the first place

[anda_skoa]

You should probably consider using a different display technology, e.g. QtQuick, which is rendered hardware accelerated on the GPU.

Cheers,
_