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Subject: Re: ODF Proposal: OFFICE-4047: Allow overlap graphic property

Hi Miklos,

thank you for taking the time to answer the questions. Point B is still a problem, see below.

Miklos Vajna schrieb am 11-Nov-20 um 08:59:
Hi Regina,

On Tue, Nov 10, 2020 at 10:12:24AM +0100, Regina Henschel <rb.henschel@t-online.de> wrote:
the ODF TC has discussed your proposal OFFICE-4047:
https://issues.oasis-open.org/browse/OFFICE-4047. There are some aspects in
the proposal, which are not clear.

(A) What happens if only one of the overlapping objects has set

Thanks for these questions. As in many other cases, this attribute is
modeled after an existing OOXML feature, so the intention is to document
what's already the case there. This usually looks simple at first, but
then it's easy to forget about corner-cases.

In case there are 2 overlapping shapes and only one of them sets
draw:allow-overlap="false", then shapes should be positioned in a way to
avoid the overlap.

(B) In which way should the application solve the conflict? Please consider
LibreOffice bug https://bugs.documentfoundation.org/show_bug.cgi?id=134115
in this regard.

The OOXML spec is not crystal clear on this:

"If a DrawingML object cannot overlap other DrawingML object, it shall
be repositioned when displayed to prevent this overlap as needed."

Experimenting with Word, I found what is mentioned at

"If there is an overlap, then a shift towards the bottom or towards the
right would resolve that. Word seems to always push down, do the same
for compatibility. >
I imagine never shifting towards the top or left is helpful to avoid
layout loops, because this means we always progress towards to bottom
right corner of a page.

I do not see this behavior in Word. Take for example the attachment from tdf#134115 [https://bugs.documentfoundation.org/attachment.cgi?id=162173]. There the object is shifted to the left.

I have ask in the forum now. Perhaps that helps.


(C) Which object is changed? Depending on mark-up position, on z-order,

I experimented with overlapping shapes where allow-overlap was true for
both shapes. Let's say there was a red shape and there was a green shape
on top of it. Then it did not matter which shape was changed to
allow-overlap=false, the red shape was re-positioned. So I guess the
intention is that the one which is behind other shapes is re-positioned.

I cannot confirm. In the above mentioned test document, the "red frame"-object is moved to the left,

(D) How does this new attribute interact with the attribute

My understanding is that wrap-influence-on-position has 3 possible
choices: once-successive, once-concurrent and iterative. Writer defaults
to once-concurrent and this is never set to an other value for
imported-from-Word documents. So I believe that iterative or
once-successive is only for compatibility for older documents; there was
even some specification on the OOo site regarding this, though now I
can't find it.

So my expectation is that at least the LibreOffice allow-overlap
implementation is only tested with the
draw:wrap-influence-on-position=once-concurrent case. Just to simplify
life for everyone, perhaps it would make sense to explicitly say that
allow-overlap should be ignored if draw:wrap-influence-on-position is
not once-concurrent?

Would you please be so kind and answer the questions or extend your
proposal? You can answer to the mailing list or in OFFICE-4047.

I hope the above helps: as you see the intention is to extend ODF in a
way that documents imported from OOXML don't loose their allow-overlap
property. Of course you're right, just because OOXML did a poor job at
documenting their behavior, it's not an excuse for ODF to do the same.



Giving no rules for reposition makes interoperability harder. Let see, whether there are some useful answers in the forum.

Kind regards

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