DynamicheadersandfootersinFOPdoc在fopdoc动态标题和页脚.doc

Dynamic headers and footers in FOPDynamic headers and footers in FOP1Preface1The problem1Why we need separate solution?1The objectives of PDF generation1The solution2Intermediate calculations2Positions inside table headers and footers2Values substitution3Known limitations3Feedback3PrefaceThe problemFor such tasks we need provide such intermediate calculations, and make separation of table headers and footers by position.(first, last, odd, even or direct number). Unfortunately, the existing process of PDF/QXP/InDesign generation prevents make easy and flexible solution. To imitate the same functionality, we need produce tables with fixed row heights, make complex templates, and make several tables rather one with proper table header/table footer customization.Why we need separate solution?The existing particular solutions require complex layouts, slave templates, and many tables to imitate one. The typical way contains: At least two (or three) tables or even two or three layouts (in case of multi-layout based solution) with the same (or similar) content Additional templates to make intermediate calculations Fixed row heights to be sure the required data have placed accurately Table header/table footer imitations with appropriate templates Slave tables to make such “brief/total” results.So we need a lot of technical details implemented manually with appropriate complexity of layout modifications.The objectives of PDF generationThe PDF generation process is based upon sequential and determined scheme described below:XSLT processor (Saxon)XSL-FO render engine (FOP)XMLXSLXSL-FOPDFAs you can see the PDF generation requires such independent steps to make. Every step provides its own data processing. At first step named XSLT the raw data (XML) with appropriate stylesheet (XSL) have being converted to well-formed XSL-FO document with detailed descriptions of every logical unit, such as page, page headers and footers, tables, static blocks, etc. At this time the logical markup have done; and for most cases it can be converted to physical form (PDF) as is. But we have few interceptions in this well-formed scheme; there are page overflows. This issue has performed later at the render phase. Unfortunately, at render phase we havent any data from previous step (XSLT phase) so we cannot perform any intermediate calculations here. So we have two issues must be pre-calculated and post-calculated at the other phase. Any intermediate calculations, such as summarizing, averages, differentials and any other must be done at XSLT phase. And table headers and table footers will be generated later, at render phase.The solutionIntermediate calculationsAll types of intermediate calculations must be provided by appropriate Saxon extensions, as the appropriate raw data is available only at XSLT phase. At this time we need to prepare all data for further rendering.For example, we can calculate intermediate summarizing by At the time of XSLT Saxon will calculate intermediate sums and place it to appropriate headers and/or footers of table. As user may require any complex calculations here, we cannot provide anything other in XSLfast as it already has.The same use case can be suggested for totals calculations; the separate table with appropriate “XPath” expressions inside will provide any kinds of proper calculations without any mis-features inside.Positions inside table headers and footersAs most commonly used task we need to make booklets, brochures, and other printable forms with first, last, odd and even page separation. And for usual cases the differences between these pages are main table headers and footers form. To make this solution more accurate and user friendly, we would provide FOP extensions for table headers and table footers.Every table will able using three different kinds of table header/footer placements independently of other pieces of data. There are “first”, “rest”, “odd” and “even” placement forms. For example, the following forms are applicable:So you will able specify wide list of differences for every table in one place. In fact, every fox:dynamic-table-header or fox:dynamic-table-footer might be completely different in comparison of each other. It might support different colors, different styles or even different content.Values substitutionOne of possible ways to make value substitution is using Saxon extensions like the examples above demonstrated. Unfortunately this way is context-sensitive and limited to XSLT. If we need to combine all three points of task we need another way to collect and fetch intermediate values within XSL-FO.The one of possible ways to organize map-like structure in XSL-FO like the following example:In appropriate templates we would expand values likeThe intermediate value X1 = This way will make us ability to fill out the intermediate results within XSLT phase into specific map inside XSL-FO, and will get us ability to refer the values were stored at XSLT phase within rendering phase.Known limitationsThe proposed method to improve FOP has the following limitations: FOP have no ability to resolve “last” page and “last” table piece, so the position “last” arent supported. FOP have support of “first” + “rest”, “odd” + “even”, and “first” + “odd” + “even” combinations only. The “rest” attribute might be used only with “first” placement type. The values substitution will not applicable for attribut