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

[Tommytrojan]

Which update() do you call?

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. I would like to not have to go through the formatting if the item is not being displayed anyway. So what I want is:

fOnData(char* szData)
{
  if !isObscured()
  {
    fFormatData(szData);
    update();
  }
 
  // Ignore data as it is not rendered anyway
  else
  {
  }
}

fOnData(char* szData)
{
  if !isObscured()
  {
    fFormatData(szData);
    update();
  }

  // Ignore data as it is not rendered anyway
  else
  {
  }
}

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If the items gets uncovered and a paint even issued I can recover the data and do the formatting then. The data events occur with a 100ms frequency and there can be thousands of them, so it is important to not incur this overhead until it is really needed.

Thanks,
Tom