[poppler] Question on how to ensure API compatibility

[Albert Astals Cid]

El Diumenge, 5 d'agost de 2012, a les 17:16:46, Adam Reichold va escriure:
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> On 05.08.2012 16:36, Ihar `Philips` Filipau wrote:
> > On 8/5/12, Albert Astals Cid <aacid at kde.org> wrote:
> >>> Exactly, that's why I am unsure whether I can change
> >>> 
> >>> QImage renderToImage(double xres=72.0, double yres=72.0, int
> >>> x=-1, int y=-1, int w=-1, int h=-1, Rotation rotate = Rotate0)
> >>> const;
> >>> 
> >>> to
> >>> 
> >>> QImage renderToImage(double xres=72.0, double yres=72.0, int
> >>> x=-1, int y=-1, int w=-1, int h=-1, Rotation rotate = Rotate0,
> >>> bool multiThreading = false) const;
> >>> 
> >>> in "Poppler::Page" defined in "qt4/src/poppler-qt4.h" without
> >>> breaking something. Recompiling is obviously fine, but would
> >>> applications that were linked against Poppler before that
> >>> change still work?
> >> 
> >> No, they wouldn't.
> >> 
> >> Here a nice overview of the dos and donts.
> >> http://techbase.kde.org/Policies/Binary_Compatibility_Issues_With_C++
> > 
> > Extremely valuable link. Thanks.
> > 
> > On topic. Quote from the link: -- If you need to add extend/modify
> > the parameter list of an existing function, you need to add a new
> > function instead with the new parameters. In that case, you may
> > want to add a short note that the two functions shall be merged
> > with a default argument in later versions of the library:
> > 
> > void functionname( int a ); void functionname( int a, int b );
> > //BCI: merge with int b = 0 -- The open question is whether the
> > "need" is there.
> 
> For a simple document (some mathematical text), the average time for
> the rendering alone goes from *(46 +- 10) ms* per-page (using Poppler
> 0.20.2) to *(69 +- 20) ms* per-page (using Poppler master with Thomas'
> patch) on my system. (Using 100 samples in both cases.)

Well, 20 msec is something i can live with, i'm more scared on "big documents" 
if it adds something like one second or half a second :D

> I changed Poppler::Page::renderToImage to just create a temporary
> SplashOutputDev for every call and used the fMT flag, so the overhead
> is probably mostly creating the output device. Not sure whether
> caching the output device in PageData is good idea... (I think it
> would be ideal to have as many output devices as rendering threads but
> IMHO that would imply too close a coupling to the application using
> the library.)

Yeah well, creating an SplashOutpuDev is not "cheap" since it creates the 
SplsahBitmap and Splash.

> Maybe you could tell what kind of data you'd like to see so that I
> could try to provide it? Not sure how helpful such a simple average is.

Well, as far as i can see the only overhead is the copying of the xref, what 
about a program that calls the xref copying function so I can call it over all 
the thousand pdf i have lying around to see how much time takes on them?

Albert

> 
> > Wrt, multithreading. Just a thought. I had impression that it
> > should be already possible to create a private instance (per
> > thread) of the document for the same PDF, so that the threads can
> > rasterize the pages of the same PDF in parallel. Only trade off is
> > the memory consumption.
> 
> We previously did this in qpdfview but I don't like the idea of
> reparsing the document over and over to render each page. It also adds
> problems for password-protected documents and the semantics of what
> happens when the file changes on-disk are different.
> 
> Regards, Adam.
> 
> > _______________________________________________ poppler mailing
> > list poppler at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/poppler
> 
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