On 16.01.2010 00:04:32 Jonathan Levinson wrote:
> Using PDF Vole to examine the PDF files and reading the PDF
> specification, I've come to the conclusion that PDF renderers such as
> Adobe Acrobat version 9.0 do not implement BIDI or glyph form shaping.
> Rather it is the job of the software that produces the PDF to ensure
> that the glyph drawing commands in left to right order pick the right
> glyphs and implement BIDI and paragraph line-breaking appropriately. 
> Glyph form shaping (the choosing of the right glyphs for initial,
> intermediate and final forms) also has to be done by the software that
> produces the PDF.

That's the impression I have, too.

> This means that adding Arabic support to FOP will involve at least the 
> following areas:
> 1) Change of layout manager to support line-breaking on the left.
> 2) Integration of line-breaking in layout manager with BIDI algorithm to 
> appropriately handle quoted strings.
> 3) Automatic recognition of right-to-left direction from UNICODE font rather 
> than specifying text direction through writing-mode.
> 4) Implementation of form shaping glyph chooser in PDF rendering engine.
> 5) In PDF rendering engine - rearranging texts in Tj command so that they 
> correspond to BIDI algorithm.  Rearrangement has to be done on a character by 
> character basis for instance Arabic text (rendered right to left) can contain 
> numbers (rendered left to right) or quote French (rendered left to right).

Not to forget the area tree (and intermediate formats) which has to
support that. Keeping the door open to implement tb-lr is probably also
something that should be kept in mind when tackling that.

> Best Regards,
> Jonathan Levinson

Jeremias Maerki

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