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From "Stephan Thesing" <thes...@gmx.de>
Subject Re: Implementing Change bars
Date Wed, 02 Sep 2009 18:22:21 GMT

just a short status / question update.

I have added the fo:change-bar-begin/end elements with their properties.
Validation is also implemented, but:
 - In contrast to the other fo: elements, the change-bar-* elements
     are allowed to occur everywhere, as long as they have an
     fo:flow or fo:static-content ancestor.
   All the elements do their content validation via validateChildNode()
     (e.g. Block.java in o.a.fop.fo.flow).
   As I didn't want to add acceptance of change-bar-* children to all
    fo: elements under o.a.fop.fo.flow, I added to FNode.java a
      validateChildNodeGlobal() function that performs the "global"
      check for change-bar-* children and then calls validateChildNode()
      to perform the local check for each element.
    in FOTreeBuilder.java this is then called instead of 
    The version of validateChildNodeGlobal() applicable for change bars
      is added in FObj.java

Validation of the stacking constraints of change-bar-begin and -end are
also done.
Error messages and codes for validation errors are also already added.

What remains is layout and producing the change bar areas.

If I read the spec right, the intended semantics of the change-bar-elements is the following:
 - for all elements generating areas that are under the influence of
     a change bar, add fixed areas as tall as the generated areas and
     placed beside the column of that area as given by the change bar
 - "being under the influence of  a change bar" is defined by the file
    order of elements in the input.
   I.e., any element between a change-bar-start and corresponding change-bar-end (same class)
is influenced by that change bar.
   For me, that means that an element can be under the influence of multiple change bars,

My idea is now along the following lines:
 - Remember for each element during parsing the change bars it is influenced by.
 - After layout, go over all areas produced by those influenced elements
    and add the areas for the change bars (thus, only an area with proper
     border attributes).

Can this be realizes in such a way in FOP?

I appreciate any comments and suggestions!

I will be able to produce a first diff of my code this weekend.

Best regards...

> - retrieving the start- and end locations of the bars during layout
>   (org.apache.fop.layoutmgr)
> - creating the appropriate areas (will probably have to be done in
>   o.a.f.layoutmgr.PageSequenceLayoutManager)
> That should be enough to get you started. If you have any question, see
> you on fop-dev!
> Vincent

Dr.-Ing. Stephan Thesing
Elektrastr. 50
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