Date: 2005-03-04T01:28:38
   Editor: JeremiasMaerki
   Wiki: XML Graphics - FOP Wiki
   Page: PageLayout/InfluenceOfPageSizesOnAlgorithm

   Influence of different page sizes on the pagination algorithm to be developed

New Page:

= Influence of different page sizes on the pagination algorithm to be developed 

XSL-FO allows arbitrary sequences of different page specifications. The 
consequence is that you may have different available IPDs for any page.

Many of the papers we found on pagination don't seem to deal with this fact. 
They focus mainly on formatting books where each page has the same available 
IPD. That allows for prefabrication of the vertical box lists and only the page 
breaking decisions have to be made and the individual boxes distributed over 
the pages.

An example found in [1], chapter 2.1: "As to the text stream, we assume that 
the line breaking task has already been completed. Afterwards, each paragraph 
consists of a sequence of line boxes and vertical glue boxes."

If we consider the possibility of different available IPDs over pages/regions, 
we can see that for each possible page break a different set of vertical boxes 
is generated on the subsequent page. This gets worse if a total-fit algorithm 
is chosen and a whole page-sequence is considered. The number of combinations 
grows exponentially.

If the available IPD remains equal between pages (which is true for most 
documents) look-ahead is possible and bearable from the performance POV. If a 
look-ahead algorithm is chosen, it must be capable of switching off look-ahead 
if subsequent pages have different available IPD, thus reducing it to a simple 
best-fit or first-fit algorithm. So if the available IPD remains equal the 
generated vertical boxes can be reused on a subsequent pages, they only have to 
be discarded if the IPD changes.

It remains to be determined if side-floats have an impact here. Probably not, 
since they mostly affect only the present page and there only the line-breaking.

[1] Brüggemann-Klein, Klein, Wohlfeil: On the Pagination of Complex Documents,

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