On Nov 15, 2006, at 11:41, Vincent Hennebert wrote:

Hi Vincent,

Just to let you know that I'd like to finish the implementation of the
collapsing border model.
I've started to look at the wiki pages, the code and the mail archives
but if you have any hint about what are the remaining problems to solve,
where to look at in particular, etc., I'm all ears ;-)

Collapsing borders again, ay? 8)
Well, I still have some ideas up my sleeve for optimization, but AFAIU the basic implementation that Jeremias initially added should work nicely, except for the part that is documented on the Wiki.

Unfortunately, I haven't had too much time lately to invest into this, but roughly it comes down to moving a great deal of the collapsing-border-logic to the FOTree. I've had numerous fruitful discussions with Jeremias about this in the past, and I'm still convinced that it would be a good move --performance-wise-- to relocate those parts to the FOTree, and make them accessible to the layoutengine from there. Although it is almost never possible to resolve the borders completely at that stage, since you have no page-breaking context yet, I still feel much for performing as much of the resolving as possible before the layoutengine even gets its hands on those FO nodes.

It's not a BIG problem, but still it seems like a waste to have a table with potentially thousands of cells, each one having a CommonBorderPaddingBackground with BorderInfo objects that basically all have the same properties (width / color / style), so my ideas go in the direction of reducing the number of separate BorderInfo instances drastically. If, for example, the table's start-borders would win for all rows, then it seems logical to me that all the cells adjacent to that start-edge actually share that very same BorderInfo instance.

Another way to go about that would be to implement BorderInfo as a fly-weight, so that even when there are many different tables with identical border-properties, there is actually only one BorderInfo alive to which all the related FO nodes share a reference...

That said, these ideas for improvement can easily wait until we have a fully working implementation to begin with, so go right ahead with this. The community is going to love you for it (if you still needed motivation ;) )

Cheers,

Andreas

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