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| <document> |
| <header> |
| <title>Layout managers</title> |
| <authors> |
| <person name="Peter B. West" email="pbwest@powerup.com.au"/> |
| </authors> |
| </header> |
| <body> |
| <section> |
| <title>Layout managers in FOP</title> |
| <p> |
| What do the layout managers do? Most layout is is "automatic" |
| in the sense of being a straightforward stacking operation. |
| Sibling inline-areas, including fo:character areas, are |
| stacked in line-areas in the inline-progression-direction. |
| Sibling block-areas, including line-areas, are stacked in the |
| block-progression-direction. |
| </p> |
| <p> |
| In the simple cases in which both the available |
| block-progression-dimension and the available |
| inline-progression-dimension are known, this process can be |
| driven bottom-up. Available dimensions trickle down from the |
| top, and the bottom level galleys can determine when their |
| available areas are full and suspend pending the arrival of |
| more areas. Such full notifications bubble back up the tree |
| of active galleys. E.g., if an inline galley fills a |
| line-area of a given inline-p-d and suspends while still |
| within the available block-p-d, the parent block-area galley |
| will simply stack the inline-area and notify the inline galley |
| to continue. If the inline-galley discovers that the next |
| line-area that it would generate will not fit in the the |
| block-p-d, it suspends with a notification to that effect to |
| its parent. |
| </p> |
| <p> |
| In more complex cases the dimensions may not be fully |
| specified, or decisions about layout may depend on later |
| layout. In all such cases some layout look-ahead is required |
| which can report results back to higher layout levels. The |
| job for a layout manager in these cirucmstances is to evaluate |
| the information flowing back and set parameters for the best |
| fit layout. |
| </p> |
| </section> |
| </body> |
| </document> |
