again QGraphicsView performance

[wysota]

I'm sure that my updates are synchronized.

How do you know that?

All them called from gui thread.

Which doesn't mean they are synchronized. I'm not talking about threads but about doing a single update of your view instead of three.

[medved6]

Which doesn't mean they are synchronized. I'm not talking about threads but about doing a single update of your view instead of three.[/QUOTE]

Ok. How can I know/check that ?

[wysota]

If you didn't do anything to synchronize updates then they are probably not synchronized. You need to make sure all items are updated upon the same timeout from the same timer.

[medved6]

I see what you mean. It is better to call as much updates as possible per one time..., not separately.

In my apps it works like this... For each video window I have it's own thread. This thread decodes video comming from some quue, and calls some signal. The slot for that signal is function im gui thread, calling update().
Some video has 20.5 fps, some 33.67fps, some 4.5 fps... Video shoud be displayed smooth.
So I'm not sure can I synchronize updates.

[wysota]

Use a timer to synchronize updates.

[medved6]

I said I can not. I need to draw image as soon as possible, do not wait.

[wysota]

In that case you have to live with big cpu usage. You can't eat a pie and still have the pie. You either show all images at the same moment of time or not. If not then you have to redraw the same image many times hence slowing down the application. By the way, I'm sure that if you display the camera image 5ms later than "immediately" nobody would notice. But suit yourself.

[medved6]

Ok. Thank you for the advice! I'll see if it helps, it's easy to try.
Let you know here. Thank you again!

[medved6]

Thank you.
You advice about update synchronization was very helpfull. The problem is solved.
Now I have linear increment of CPU usage with every new video. No metter how many cams do I have I do updates ( if needded ) at one shot every 25 ms.