[poppler] Implement overprint in qt interface?

Albert Astals Cid aacid at kde.org
Mon Oct 22 15:56:26 PDT 2012 

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

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)

Do not set the overprint hint if isOverprintPreviewSupported is false

Rename the getXBGRPtr to convertToXBGRPtr since it does a lot more than what 
you'd expect a getter to do

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
> >>>>> 
> >>>>> .
> >>> 
> >>> _______________________________________________
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> >>> http://lists.freedesktop.org/mailman/listinfo/poppler
> >>> 
> >>> .
> >> 
> >> _______________________________________________
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> >> http://lists.freedesktop.org/mailman/listinfo/poppler
> > 
> > _______________________________________________
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> > 
> > .
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