Hi Bertrand,

The layout methods and how they work are subject to change with the layout 
process. So don't read too much from these methods.

A visitor pattern sounds right. Instead of building the fo tree and then 
using the layout managers to create an area tree. Use a structure renderer 
to read from the fo tree.

Fo each element in the fo tree when creating we call: start, 
handleAttributes and end. We should be able to put the visitor in various 
sections depending on the type of element and the layout managers may also 
be able to operate in the same areas (ie. have a common interface).

We want to be able to process elements as soon as possible and dispose of 
used data so it should be something that can work from the area tree at 
early stages.


On 2001.12.17 13:53 Bertrand Delacretaz wrote:
> Hi team,
> I started looking at the FOP source code in more detail last week, and
> from
> what I understand at this point I think it would make sense to integrate
> jfor
> as a "structure renderer" right after the FO Tree building stage.
> At this point my idea would be to:
> a) add a Visitor pattern mechanism to visit the FOTree independently of
> layout operations
> b) split layout() methods in two, adding a method called
> "getProperties()" or
> something (see details below)
> c) implement a Visitor that would generate RTF from the FOTree, calling
> getProperties() on the way
> d) maybe having getProperties() do its work only once even if called
> multiple
> times, and calling it both before the Visit and at the start of layout()
> Of course, this shouldn't be limited to jfor, the FOTreeVisitor should be
> reusable for other output formats.
> Does this sound like I'm on the right track?
> - Bertrand
> Appendix: layout() method discussion.
> For what I've seen in the source code, some computations (property
> resolution, if I understand right) done in the layout() methods would
> need to
> be moved to a "pre-layout" stage: maybe breaking layout() in two.
> Taking flow.Block as an example:
> void layout()
> {
>   . . .stage 1): properties acquisition
>   this.align = this.properties.get("text-align").getEnum();
>   this.alignLast = this.properties.get("text-align-last").getEnum();
>   this.breakAfter = this.properties.get("break-after").getEnum();
>   . . .more property reading
>   . . .stage 2): actual layout
>   int breakBeforeStatus = propMgr.checkBreakBefore(area);
>   . . .
> }

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