[Qt] How our painting on QAbstractScrollArea is done

[Paul Ishenin]

Hello,  Items specific to the Qt widget set.

Today I've spent some time to investigate how painting on 
QAbstractScrollArea should be done.

When we assigning viewport to scroll area (I dontk now actually why are 
we doing that if scroll area already create its own viewport on Init) 
that viewport reinstalled our event filter with its own and pass event 
to protected method of QAbstractScrollArea.

Here is definition of this method:
virtual bool viewportEvent ( QEvent * event )

So at moment we are doing all our painting on scroll area instead of 
viewport :)

We can ofcource install our event filter after qt installed its own 
filter for viewport, but I dont think such way things should be done (in 
my eyes this is hack).

Den, can you add that viewportEvent to QAbstractScrollArea?

I am trying to find reason of slow SynEdit painting. And I cannot find 
it. According to docs we are doing our painting in right way. But caret 
repainting takes 30%-50% cpu (depends on cpu) on big texts. I dont think 
that viewportEvent help us too much, but maybe then we can use 
QGraphicsView instead of QAbstractScrollArea for TCustomControl.

Related question is why update of QAbstractScrollArea calls not only 
paintEvent of that scroll area but also paintEvents of parent widgets?

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Best regards,
Paul Ishenin.