[Xmlgraphics-fop Wiki] Update of "AFPOutput" by JeremiasMaerki

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The following page has been changed by JeremiasMaerki:
http://wiki.apache.org/xmlgraphics-fop/AFPOutput

The comment on the change is:
A note about glyph positioning in AFP

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  One difficulty will be mapping Unicode scalar values to GCGIDs (Graphic Character Global Identifier from IBM's CDRA). GCGIDs are character names with a length of 4 to 8 characters. A large collection of Unicode characters can be mapped to GCGIDs but there's no 1:1 relationship. However, for most use cases, using this subset would probably be sufficient. So far, no machine-readable map for Unicode to GCGID could be found. A human-readable map can be found here: http://www-01.ibm.com/software/globalization/gcgid/gcgid.jsp. If you have an AFP fonts with GCUIDs (Graphic Character UCS Identifier) instead of GCGIDs, that might also work because GCUIDs just especially prefixed Unicode values expressed as 8 byte string. At the moment, the mapping from Unicode to code points (8bit inside the codepage) happens through the "encoding" setting on the font configuration element. However, that codepage file/object might also be generated by FOP.
  
+ == Glyph positioning ==
+ 
+ It is best practice to use PTOCA's SIA (Set Intercharacter Adjustment) and SVI (Set Variable Space Character Increment) structures for glyph positioning where possible. Only for kerning effects or fixed-width spaces should relative cursor movements be used. This is done to keep print file sizes small and performance high. However, there's a catch. Experiments have shown that there's no consensus about the interpretation of those two features. Currently, FOP uses them but the result may not be as expected on every target environment. In the new AFPPainter there are now two different implementations, one using above structures and one doing glyph positioning exclusively using RMI (Relative Move Inline). The latter is currently disabled. If the need should arise, an option could be implemented to let the user choose which implementation to use.
+ 
  == Random Notes ==
  
   * We should include resource (especially fonts) at the beginning of the print file. That makes sure the resources are available to the viewers and reduces the complex setup of fonts. Furthermore, it guarantees that the printer always has the most current font files.

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