[poppler] Annot borders

Tue Nov 26 23:51:42 PST 2013

Albert Astals Cid <aacid at kde.org> writes:

> El Dimarts, 26 de novembre de 2013, a les 21:11:11, Carlos Garcia Campos va 
> escriure:
>> I've noticed some small issues in the way we handle the border of
>> annots compared to what the spec says and what acroread does. Attached
>> are 4 patches:
>> 
>> [PATCH 1/4] annots: Remove unused AnnotBorderType from AnnotBorder
>> 
>> This is simply a cleanup, we have a base class AnnotBorder that allows
>> to create instances of it with the unknown type. It doesn't make much
>> sense and we are not using it at all, so I've removed the
>> AnnotBorderType, and made the constructor protected.
>> 
>> [PATCH 2/4] annots: Add helper function Annot::setLineStyleForBorder
>> 
>> The code to set the line width and dash was duplicated in several draw()
>> methods, so I've moved it to a helper function. This patch also changes
>> the way we are using it. We were always ignoring the border when the
>> border with was 0, but it doesn't seem to be always correct. The PDF
>> spec says that in both Border and BS entries when the width is 0, no
>> border should be drawn at all. But some annotations like lines,
>> geometry, polygons, etc. don't use the border entry to actually draw a
>> border, but to set the line with and dash for the stroke operations. For
>> example, we were not drawing lines for annots with no border or with a
>> border width = 0, but acroread does, because in this case the border
>> entry is used to set the line with and dash pattern, and the PDF spec
>> also says that a line width of 0 should be drawn as the thinnest line that
>> can be rendered at device resolution: 1 device pixel wide.
>> So, for FreeText annotations where we actually draw a border, we only
>> call Annot::setLineStyleForBorder if we have a border and the width is
>> greater than 0, and in all other cases we always call it when we have a
>> border. Of course, this only affects annotations not having an AP entry.
>> 
>> [PATCH 3/4] annots: Use a default border for annots that can have a BS entry
>> 
>> According to the PDF spec if neither the Border nor the BS entry is
>> present, the border shall be drawn as a solid line with a width of 1
>> point. But again, acroread seems to only apply this rule for annotations
>> that can have a BS entry. This patch moves the parsing of the BS entry
>> From the base Annot class to the specific annot classes that can have a
>> BS entry, and it creates a default border object when neither Border nor
>> Bs is present. It also removes the border passed to Gfx::drawAnnot() in
>> AnnotFileAttachment::draw and AnnotSound::draw because acroread ignores
>> the Border entry also for annots that can't have a BS entry.
>> This ensures that we always draw line, geometry, polygon, etc, even if
>> there's no border specified.
>> 
>> [PATCH 4/4] annots: Make Annot::setBorder receive an AnnotBorder object
>> 
>> Currently we can only set AnnotBorderArray objects to annots. This might
>> have no effect if the annots already has a BS entry, for example,
>> because the BS takes precedence over Border. This patches changes
>> Annot::setBorder to receive an AnnotBorder object, so that you can
>> either pass an AnnotBorderArray or an  AnnotBorderBS. Frontends should
>> always use BS when updating an annotation that can have BS entries. The
>> patch also completes the implementation of writeToObject method for
>> array borders and adds an impementation for BS borders too.
>> 
>> I've passed my tests with no regressions, 
>
> Are there improvements in rendering of some files?

Nothing changed in my tests, because most of the PDF documents either
use explicit borders or don't use 0 border widths. I noticed this
problem when reviewing the patches to add support for adding square and
circle annotations in the glib frontend. Germán told me he needed to add
a border or nothing was drawn, and that sounded wrong to me. So, reading
the spec, our code and playing with acroread I ended up writing these
patches. See bug https://bugs.freedesktop.org/show_bug.cgi?id=70983.

There might be an improvement if there were any file with a /Border in a
FileAttachment annotation, for example, since we were drawing a border
in such case, while these patches don't.

>> but I can't test the qt
>> frontend (that uses setBorder(), for example), so it would be great if
>> someone could test these patches to make sure they don't introduce any
>> regression in qt (it should build in any case).
>
> Why would it introduce any regression?

Because qt is the only frontend using Annot::setBorder() and I've
changed that. I don't mean regressions of rendering existing files, but
annotating files. I don't even know how Annot::setBorder() is used in
qt, I just grepped and saw it was used.

> Cheers,
>   Albert
>
>> 
>> Leonard, please, feel free to correct me if I'm wrong in any of my
>> interpretations of the PDF spec.
>> 
>> Regards,
>
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-- 
Carlos Garcia Campos
PGP key: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x523E6462
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