[poppler] Filled text field data not visible in saved document

Carlos Garcia Campos carlosgc at gnome.org
Sun Oct 14 01:45:10 PDT 2012

Excerpts from Fabio D'Urso's message of dom oct 14 02:49:09 +0200 2012:
> On Tuesday, September 18, 2012 07:52:23 PM Albert Astals Cid wrote:
> > El Dimarts, 18 de setembre de 2012, a les 07:49:05, vau escriure:
> > > Hi Albert, Hi Fabio,
> > > 
> > > the solution from Fabio worked quite well to me.
> > > There are still some PDFs remaining which do not have their application
> > > stream changed - at least it looks like that.
> > > 
> > > But for most of the files I tried it works fine.
> > > Hence, a big "thank you" to Fabio and I would recommend to apply that
> > > patch to an upcoming release.
> > 
> > Spoke with Fabio in private and he seems not to be happy with it, he'll be
> > working in a better one once he gets a bit of time.
> Here we go. I've rewritten the patches in a cleaner way and now I'm satisfied 
> with them.
> Short recap: After filling and saving a PDF form, filled text fields are still 
> shown with their old value (usually blank) in acroread (and in poppler too,
> when you open the resulting PDF file) because we don't update the annotation 
> widgets' appearance streams.
> With these patches, the appearance stream gets rewritten for text and 
> choice fields (for button fields it's not necessary).
> Note that choice fields still don't work in acroread, because of some 
> unrelated issues that I'll discuss in a new thread.
> Patches in detail:
> 0001
> Patch 0001 adds a AnnotWidget::updateAppearanceStream() method that is called 
> by form handling code to inform the widget annotation that its appearance 
> stream is no longer valid and needs to be rebuilt.
> This information was previously obtained by the widget annotation by testing 
> field->isModified() before drawing. This new "push" approach has two 
> advantages:
> 1) The appearance is now rebuilt only once after the contents are modified. 
> Previously, field->isModified() stayed always true, even after the first 
> draw() call, causing the apperance stream to be rebuilt on every subsequent 
> draw() call too, even if contents stayed the same.
> 2) It gives the possibility to react to modifications immediatly, without 
> having to wait for the next rendering.
> 0002
> This patch creates the new appearance stream in 
> AnnotWidget::updateAppearanceStream() and writes it in the xref. This patch 
> fixes the original bug, but...
> Note: ...every time the field is modified (eg in okular it happens every time 
> the the user adds or removes a character) the old apprearance stream is 
> deleted and a new one is generated. This means that the xref entry for the old 
> appearance is freed and a new one is allocated. Since every time a xref entry 
> is freed its generation number gets incremented, repeated edits result in 
> generation numbers rapidily growing. The next patch solves this issue.
> 0003
> This patch avoids going through xref entry deallocation+allocation on every 
> modification. Now it only happens the first time, and references to the newly 
> allocated xref entry are kept, so that subsequent updateAppearanceStream 
> invocations can do a simple overwrite instead.
> These patches are supposed to fix exactly the same documents that the previous 
> proof-of-concept patch fixed. Please let me know if you find any difference.

Thanks Fabio!, patches look good to me. If nobody objects I'll commit
them to both master and poppler-0.20 branch.

> Thank you,
> Fabio
Carlos Garcia Campos
PGP key: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x523E6462

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