Referring back to my earlier notes on layout transactions, consider the situation in which the attempt to layout a line-area from some block is rejected because the receiving page is full. Assume, for the purposes of the argument, that this occurs with a nested set of FOs. One page fills, and another must be provided, while a nest of FOs has pending output. This situation determines the essential logic of the processing.
The layoutPageSequence action starts a PageMaker, possibly as a thread of its own, and then proceeds with the page-sequence processing, pulling elements from the buffer as required. These begin with the static-contents, which, harking back to another earlier message, are simply buffered for later processing and possible merging with buffered maker subtree events.
When these are out of the way, the action gets the flow, and starts to pull the content blocks of the flow. As each top-level block is found, the contents of that block are recursively laid out. More detail of this process in the next diagram. Note that at this stage, nothing is known about the containing page.
Eventually the top-level block layout action demands page space. This is where the min/max requirements will make themselves known. Such demands from a top-level block within a flow are passed to the PageMaker. When the first of these demands, or the first demand after a page has been filled, is encountered, no page exists to receive the block contents. The PageMaker consults the LayoutMasterSet.pageFactory for a new page, and constructs the page and region viewport and reference-areas. These are then available as receptacles for the contents of the top-level blocks.
The current and subsequent top-level blocks then negotiate space requirements, acting as go-between to the PageMaker and its own descendants.
Peter -- Peter B. West http://www.powerup.com.au/~pbwest/resume.html
<<inline: LayoutPageSequence.png>>
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