Maruan Sahyoun commented on PDFBOX-4189:

The patch is a great and - given several questions we had in the past - 
important addition to PDFBox.

On the longer run I'd see some additions we might conceptually already think 
about and/or start introducing in the public API. As I haven't reviewed the 
patch the below list is meant to be a hint for possible addition. They may 
already be included

For correct text positioning using mixed language information from the 
following tables might be useful:
- GPOS: to adjust the glyph position
- BASE: baseline offsets on a script-by-script basis.
- JSTF: justification information, including whitespace and Kashida adjustments.
- BIDI Mirroring: https://www.unicode.org/Public/10.0.0/ucd/BidiMirroring.txt

To allow the user to override the language system identified by the script 
being used we might want to add {{setLanguage/getLanguage}} so that can be 
called prior to {{showText}} if an override needs to be done.

Putting that into an internal {{layout}} method as John suggested would also 
allow us to put it behind a feature flag where one could enable/disable the 
processing. We might also mark that feature as **experimental** and specify 
which languages it has been tested with (to some extend).

> Enable rendering of Indian languages, by reading and utilizing the GSUB table
> -----------------------------------------------------------------------------
>                 Key: PDFBOX-4189
>                 URL: https://issues.apache.org/jira/browse/PDFBOX-4189
>             Project: PDFBox
>          Issue Type: New Feature
>          Components: FontBox, PDModel
>            Reporter: Palash Ray
>            Priority: Major
>         Attachments: Bengali-text-after.pdf, Bengali-text-before.pdf
>   Original Estimate: 336h
>  Remaining Estimate: 336h
> Implemented proper rendering of Indian languages, which need extensive Glyph 
> substitution. The GSUB table has been read and used effectively to replace 
> some compound words with their respective Glyphs. All tests are passing. I 
> have tested this for the Bengali font. Please review these changes and let me 
> know if it makes sense to incorporate these.

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