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From Andreas Delmelle <andreas.delme...@telenet.be>
Subject Re: Implementing Change bars
Date Wed, 19 Aug 2009 20:07:03 GMT
On 14 Aug 2009, at 08:53, Stephan Thesing wrote:

Hi Stephan,

> Has anybody started to integrated support for the 1.1
> fo:begin/end-change-bar elements into FOP?

Not really, but I did have a closer look at some of the requirements  
in the XSL-FO Rec. a while ago, and in my local sandbox, I seem to  
have already created the FObj subclasses at that point, too... :) Not  
very much help, but I can send them to you, if you like.

Good thing is that there is relatively little work on the property  
side. No properties requiring special validation, and the symbolic  
literals for all the new enums (o.a.fop.fo.Constants.EN_xx) and  
properties (PR_xx) have already been committed to Trunk a while back.  
Only FOPropertyMapping needs to be updated to map the additional  
property constants to an appropriate Maker.

One thing in particular I remember are the validation rules, which  
could turn out to be tricky to implement, since the change-bars  
actually form a (possibly nested) structure 'outside' the well-formed  
XML tree.
It even seems possible (IIRC?) for a change-bar-begin to appear in one  
page-sequence, and its corresponding change-bar-end in the next... It  
will require a sort of stack to keep track of the last change-bar- 
begin (in FOEventHandler, or maybe it belongs more in  
FOTreeBuilderContext?), and it is important that this is not cleared  
after the layout for the page-sequence ends.

For the rest, it could turn out to be pretty straightforward, since it  
does not really /affect/ layout.
As Vincent already pointed out, it will need to /involve/ layout  
though, as we would somehow need to mark that the ancestor flow area  
(page or column) needs to be decorated at the start/end side, starting  
at a given position in the column/page.
No real areas need to be generated, IIC. At most dummy areas, since  
the change bars are actually no more than additional borders. I wonder  
if we could get away with partial border painting on the existing flow- 
area(?)


HTH!

Regards,

Andreas Delmelle
mailto:andreas.delmelle.AT.telenet.be
jabber: mandreas@jabber.org
skype: adlm0608

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