[Okular-devel] Dt. 4th August - status

[Albert Astals Cid]

El Diumenge, 4 d'agost de 2013, a les 23:31:02, Jaydeep Solanki va escriure:
> Hi,
> 
> Regarding the TextDocument threaded rendering issue, I implemented a clone
> method to return an EpubDocument. QTextDocument::clone() is not a virtual
> method, so either we'll have to make it virtual or change the signature of
> clone method in EpubDocument.
> I made QTextDocument::clone() virtual.

You can't do that. It will change the ABI of Qt and that's simply not 
acceptable.

> It worked fine, but despite of all the optimizations I can do, it takes
> around 400 to 500 ms to clone & 600 - 700 ms to draw, which is huge! I
> checked QTextDocument::clone() it is a bit faster (because it has direct
> access to the private classes), but won't make any difference.
> 
> To make it even faster I tried it without cloning ( kept mutex locking ),
> it takes around 200 to 500ms, still bad. Finally, to get an estimate about
> what it takes without threading, I tried the non-threaded version, & to my
> surprise it broke all records 0 to 100ms depending on the content.

That is weird, why would locking take 400ms?

> Here I learnt one thing, drawing from a just cloned QTextDocument takes
> more time, and I guess that's because of the cachedResources.
> 
> I even tried QAtomicPointer, but it breaks at several places.
> 
> I tried a lot to make it work faster, because I know you have announced it
> in Acadamy that Okular will be getting threaded rendering for
> QTextDocument, but may be for now it is better to leave it single threaded.

Don't worry, It was a BoF with around 5 people. If it can't be done, it can't 
be done.

*BUT* on the other hand even having a slower version that is thread is 
interesting since it means the UI doesn't get blocked. We may think if it 
makes sense to do the "viewport requests" in the UI thread for the speed and 
the "preloading requests" in the non-UI thread for UI smoothness.

Cheers,
  Albert

> 
> Note: I used QElapsedTimer to get the estimated time.
> 
> Cheers,
> Jaydeep