[poppler] Implement overprint in qt interface?

Albert Astals Cid aacid at kde.org
Wed Oct 24 09:45:12 PDT 2012 

El Dimarts, 23 d'octubre de 2012, a les 06:51:20, Adam Reichold va escriure:
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> Hello,
> 
> On 23.10.2012 00:56, Albert Astals Cid wrote:
> > El Dissabte, 20 d'octubre de 2012, a les 17:36:22, Thomas Freitag
> > 
> > va escriure:
> >> On 16.10.2012 22:57, Albert Astals Cid wrote:
> >>> El Dilluns, 15 d'octubre de 2012, a les 07:15:51, Thomas
> >>> Freitag va
> > 
> > escriure:
> >>>> On 14.10.2012 22:58, Albert Astals Cid wrote:
> >>>>> El Diumenge, 14 d'octubre de 2012, a les 19:41:26, Thomas
> >>>>> Freitag va
> >>> 
> >>> escriure:
> >>>>>> On 14.10.2012 17:21, Albert Astals Cid wrote:
> >>>>>>> El Diumenge, 14 d'octubre de 2012, a les 13:47:29,
> >>>>>>> Thomas Freitag va
> >>>>> 
> >>>>> escriure:
> >>>>>>>> Hi folks!
> >>>>>>>> 
> >>>>>>>> Is there anybody in the community who wants the
> >>>>>>>> possibility to simulate overprint in qt library? With
> >>>>>>>> the implementation of DeviceN support in splash this
> >>>>>>>> is quite easy now, so I can upload a patch.
> >>>>>>> 
> >>>>>>> Sure, why not? Let's see the patch :-)
> >>>>>> 
> >>>>>> Okay, here it is.
> >>>>> 
> >>>>> The two new methods are missing @since markers (and also i
> >>>>> think the documentation of the two methods could be a bit
> >>>>> more explanatory)
> >>>> 
> >>>> @since: I thought that You insert it when You commit it. If I
> >>>> would insert 0.22.0 You have to change it if You will not
> >>>> have the time to commit it :-) or I need to change it and
> >>>> have to upload a new patch if You will not have the time :-(
> >>> 
> >>> Well, if you do it, it's less work i have to do and thus it's
> >>> easier i'll have time ;-)
> >> 
> >> Because I removed these two new methods now there is no need to
> >> comment them anymore :-) But I introduced a new (static) method
> >> "okToUseOverprint" which just proofs if poppler is compiled with
> >> SPLASH_CMYK, and there I add the @since comment now.
> >> 
> >>>> Explanatory: Okay, but this will be hard. For those who know
> >>>> what overprint is the documentation is self-explanatory, for
> >>>> others I need to write reams. What's about to insert the link
> >>>> to http://en.wikipedia.org/wiki/Overprinting?
> >>> 
> >>> To be honest doesn't seem to make things much clearer to me :D
> >> 
> >> Okay, let me try to explain it in my own words: First of all, in
> >> the normal behaviour, if something is painted everything
> >> previously painted at this place is knocked out. This is rather
> >> simplified, because we ignore functionality like transparency,
> >> blending modes etc. Now let us have a look at the printing
> >> process with 4 different colour plates Cyan, Magenta, Yellow and
> >> Black. Without setting the overprint mode, the behaviour is the
> >> same:  if something is painted everything previously painted on
> >> every plate is knocked out. But when overprint mode is enabled,
> >> and i.e. in a DeviceN colorspace with only one process colour,
> >> let us assume Cyan, the Magenta, Yellow and Black plates kept
> >> untouched and only previously painted objects on the Cyan plate
> >> at this position are knocked out. But when You paint in
> >> DeviceCMYK, the behaviour remains the same (all is knocked out)
> >> even with overprint on, unless You set overprint mode to true in
> >> addition. With overprint mode true You need to look at the colour
> >> components You use for painting: if the a component is 0 the
> >> corresponding colour plate is left untouched again, if it is not
> >> 0 it will be knocked out again on this colour plate. If there is
> >> a additional spot colour plate, it is similar: overprint false:
> >> everything is knocked out, overprint true: if You paint with
> >> process colours only this spot colour plate is left untouched, if
> >> You paint with this spot colour, the process colour plates remain
> >> untouched but on this spot colour plate previously painted
> >> objects are knocked out. As I said, this is rather simplified,
> >> there are special rules for images, blending modes and so on and
> >> so on. A complete explanation can be found in the PDF
> >> specification. As overprint just works on colour plates, You'll
> >> see no effects when You print in RGB as on a monitor, therefore
> >> You have to simulate the effects (overprint preview :-) ) if You
> >> want to see them on a monitor.
> >> 
> >>> Ok, let's leave the docu as it is
> >>> 
> >>>>> Also why are you calling it "overprint preview"? How is it
> >>>>> a preview?
> >>>> 
> >>>> To be honest, I haven't really thought about that. Probably I
> >>>> choose that name because it is also introduced in
> >>>> GlobalParams with that name. But also in the acrobat reader
> >>>> preferences it is called "Use overprint preview". And because
> >>>> not all RIPs support it (i.e. RGB printers) it is indeed
> >>>> something like a preview (for RIPs which support it).
> >>> 
> >>> Ok, let's leave it with that name (but maybe make it a
> >>> RenderingHint as Adam suggests?).
> >> 
> >> I tried to understand what You meant with RenderingHint and made
> >> it, hopefully it is what You meant. I attach the changed patches
> >> (poppler and okular).
> > 
> > Looks good, I've made some changes (to try to make the roundtrip
> > faster if you agree to them)
> > 
> > Rename Document::okToUseOverprint to isOverprintPreviewSupported
> > like we had for the cms stuff
> 
> This seems a better way to name it as the old one would suggest it is
> a per-document property which it is not.
> 
> > Put back the thing that creates the splashoutputdev and do the same
> > we do with antialias in the hint changes but for overprint (I don't
> > really see why we need this code shuffling around, so i'm trying to
> > minimize the diff size which hopefully minimizes the impact for
> > other features than this one)
> 
> While the change is not strictly necessary, the new
> Document::setRenderHints, Document::getOuputDev and also
> DocumentData::setPaperColor show why it makes things much simpler.
> (Looking at the patch: If we add "delete m_outputDev;" to the end of
> the latter shouldn't there be a "m_outputDev = NULL;" as well?)

Yes, there is a = NULL missing, i'll add it when i find some time, note i'm on 
a business travel until Nov 1st so my time is ultra limited until then.


> I also think that there should not be any fallout from this change
> since the member "DocumentData::m_outputDev" is gone afterwards, hence
> any code that still relies on a pre-created output device would have
> been spotted by the compiler.

I'm not oposing to that change, it's just a separate change, not needed for 
this feature, let's keep features/fixes/cleanups in separate commits :-)

Cheers,
  Albert

> 
> (And there is also Thomas' threading patch which would also introduce
> those changes to the output device creation.)
> 
> > Do not set the overprint hint if isOverprintPreviewSupported is
> > false
> 
> Makes sense.
> 
> > Rename the getXBGRPtr to convertToXBGRPtr since it does a lot more
> > than what you'd expect a getter to do
> 
> I agree.
> 
> Best regards, Adam.
> 
> > What do you think?
> > 
> > Cheers, Albert
> > 
> >> Cheers, Thomas
> >> 
> >>> Cheers,
> >>> 
> >>> Albert
> >>> 
> >>>>> Given that overprint only works if defined(SPLASH_CMYK) you
> >>>>> should make the setter return a boolean that says if the
> >>>>> set worked or not (i.e. make it fail if
> >>>>> !defined(SPLASH_CMYK))
> >>>> 
> >>>> Gotcha. I thought about that and disable / enable the option
> >>>> in okular if the format generator doesn't support it. But
> >>>> because I'm not familiar enough with okular I defered it and
> >>>> then forgot it... I'll insert it in QT when I get answers to
> >>>> the other points.
> >>>> 
> >>>> Cheers, Thomas
> >>>> 
> >>>>> Cheers,
> >>>>> 
> >>>>> Albert
> >>>>> 
> >>>>>> In a few places it has already a similar implementation
> >>>>>> than in bug 50992 (thread safe), because changing the
> >>>>>> overprint option also meant that we need a different
> >>>>>> SplashOutputDev instance. But You probably also want to
> >>>>>> test it in okular? Even if we are here not on an okular
> >>>>>> list, I attach the okular patch here, too. Also here, it
> >>>>>> has already the changes from bug 50992. But because
> >>>>>> POPPLER_QT_THREADSAFE is not defined here, it doesn't
> >>>>>> make any difference, so I let these changes as they are.
> >>>>>> BTW, I'm not really familiar with qt programming, so most
> >>>>>> changes in okular are more or less a (hopefully) best
> >>>>>> guess.
> >>>>>> 
> >>>>>> Cheers, Thomas
> >>>>>> 
> >>>>>>> Cheers,
> >>>>>>> 
> >>>>>>> Albert
> >>>>>>> 
> >>>>>>>> For everybody who doesn't know anything about
> >>>>>>>> overprint I attach three screenshots which shows the
> >>>>>>>> implementation in okular. (This is not fake, I made a
> >>>>>>>> small apprentice piece today morning :-) )
> >>>>>>>> 
> >>>>>>>> Cheers, Thomas
> >>>>>>> 
> >>>>>>> _______________________________________________ poppler
> >>>>>>> mailing list poppler at lists.freedesktop.org
> >>>>>>> http://lists.freedesktop.org/mailman/listinfo/poppler
> >>>>>>> 
> >>>>>>> .
> >>>>> 
> >>>>> _______________________________________________ poppler
> >>>>> mailing list poppler at lists.freedesktop.org
> >>>>> http://lists.freedesktop.org/mailman/listinfo/poppler
> >>>>> 
> >>>>> .
> >>>> 
> >>>> _______________________________________________ poppler
> >>>> mailing list poppler at lists.freedesktop.org
> >>>> http://lists.freedesktop.org/mailman/listinfo/poppler
> >>> 
> >>> _______________________________________________ poppler mailing
> >>> list poppler at lists.freedesktop.org
> >>> http://lists.freedesktop.org/mailman/listinfo/poppler
> >>> 
> >>> .
> >>> 
> >>> 
> >>> _______________________________________________ poppler mailing
> >>> list poppler at lists.freedesktop.org
> >>> http://lists.freedesktop.org/mailman/listinfo/poppler
> 
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