Hi all, Just came across this older thread and just wanted to give my 2cents on it.
First of all, Francesco's observation is correct IMHO: My conclusion is that PoDoFo linearization support overall (read an write) has always been quite incomplete at best, and quite certainly broken/buggy enough to be disabled quite early in PoDoFo development, so that nothing is working about PDF linearization now. I think it was a good decision to remove this code in pdfmm as it is not working and having an API that is not working is just misleading. I would agree to have this code removed in PoDoFo as well, as I do not think it is possible to fix it in the current state. If someone would want to reintroduce PDF linearization for writing, a complete reengineering would be required. Best regards, Dominik On Fri, Feb 18, 2022 at 9:25 AM Francesco Pretto <cez...@gmail.com> wrote: > Hello Connor, > > I'm the maintainer of pdfmm, a PoDoFo fork, but I had to evaluate what > was done in PoDoFo about PDF linearization. I will try to answer you > in a fair way, to the best of my knowledge. First, let's clarify what > main capabilities PDF Linearization should enable, among others. > According to Annex F of PDF 32000-1:2008 the PDF linearization, : > - allows to "display the first page as quickly as possible" (not > necessarily the page 0); > - when the user requests another page of an open document it allows to > "display that page as quickly as possible". > > PDF linearization as described by Annex F is implemented by > encapsulating the content of the first page document in a "Incremental > Update" like serialization that must be at the beginning of the > document, together with a "linearization dictionary" that should be > the first object of the document. The rest of the document is appended > after this fake "incremental update" and "the pages shall be > contiguous and shall be ordered by page number", and "the objects > required to display that page shall be grouped together" and "the > order of objects referenced from the page object should facilitate > [...] incremental display of the page data as it arrives". > > Let's distinguish between PDF linearization read support, intended as > the ability to exploit the organization of a linearized PDF document > and write support as the ability to create a compliant linearized PDF. > PoDoFo attempted to have linearization read support but it was > disabled in 2009[1]. Also just reading the document structure (and not > the object content) is performing a lot of of seeks that would kill > the purpose of linearization (I actually removed those seeks in > pdfmm). > > About PDF linearization write support, which I think you are most > interested in, PoDoFo appears to do some work related to linearization > in PdfVecObjects class[2], but in all the work related to create the > linearization dictionary was disabled in PdfWriter[3] even earilier in > 2007. Also there's no sign of the needed fake incremental update that > contains the content of the first page. > > My conclusion is that PoDoFo linearization support overall (read an > write) has always been quite incomplete at best, and quite certainly > broken/buggy enough to be disabled quite early in PoDoFo development, > so that nothing is working about PDF linearization now, and the > leftover API that seems to enable linearization is just code that got > rotten (that's why I decided to remove it completely in pdfmm). If one > decided to work on revamping the PDF linearization support I would > recommend to read the specification and start it from scratch, not > basing on the left-over code in PoDoFo, but it's a weeks/months long > full time work. Of course I would love to re-introduce it in pdfmm, > where the situation is just much more clean than in PoDoFO, but > unfortunately that work is not in my top priorities. > > I hope I was factually correct about the current state of PoDoFO. > Other people may add further details or correct me if I was wrong. > > Regards, > Francesco > > [1] > https://sourceforge.net/p/podofo/code/HEAD/tree/podofo/trunk/src/podofo/base/PdfParser.cpp#l300 > [2] > https://sourceforge.net/p/podofo/code/HEAD/tree/podofo/trunk/src/podofo/base/PdfVecObjects.cpp#l308 > [3] > https://sourceforge.net/p/podofo/code/HEAD/tree/podofo/trunk/src/podofo/base/PdfWriter.cpp#l274 > > > On Thu, 17 Feb 2022 at 23:00, Connor Black <cbl...@iconect.com> wrote: > > > > Hey, > > > > > > > > I am currently evaluating this library for use in a commercial product > and I was curious what linearalization would look like using PoDoFo. I have > spent the last couple of days looking through documentation and trying to > look into how it would work but the most I can grasp is that PdfWriter has > the option to set linearalization through SetLineralization – but I have > not been able to find any examples or successfully use the PdfWriter class > to produce these results. I was wondering if you could provide a little > code snippet showing how PdfWriter would be used in that regard and maybe a > break down on how linearalization is supported using this library. > > > > > > > > Thanks, > > > > Connor Black > > > > > > > > This message and any attachments are intended only for the use of the > addressee and may contain information that is privileged and confidential. > If the reader of the message is not the intended recipient or an authorized > representative of the intended recipient, you are hereby notified that any > dissemination of this communication is strictly prohibited. If you have > received this communication in error, notify the sender immediately by > return email and delete the message and any attachments from your system. > > _______________________________________________ > > Podofo-users mailing list > > Podofo-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/podofo-users > > > _______________________________________________ > Podofo-users mailing list > Podofo-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/podofo-users >
_______________________________________________ Podofo-users mailing list Podofo-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/podofo-users
