[poppler] Annot borders

[Carlos Garcia Campos]

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, 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).

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