Am 05.08.2012 17:26, schrieb 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 <[email protected]> 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?
Just call displayPageSlice with fMT = gTrue (small modification in
pdftoppm, see my testcase) and You should see how much time it takes.
Thomas
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.
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