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https://issues.apache.org/jira/browse/PDFBOX-4189?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16438540#comment-16438540
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John Hewson edited comment on PDFBOX-4189 at 4/15/18 12:17 AM:
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Hi guys, this is a really welcome contribution, thank you. With regards to
PDFont#encode(String text) being non-final I can add some insight as I was the
original designer of our current PDFont#encode mechanism.
Basically, the PDFont classes are designed to represent fonts identically to
how they are represented when embedded in PDF files. So there's no support for
OpenType, by design. A Type0 font knows nothing about OpenType.
So how can we use OpenType in PDFBox? The answer is that we do it one layer of
abstraction up, during text _layout_ instead of text _encoding_*_._* So you
want to put your glyph substitution code inside PDPageContentStream#showText,
actually you want
[PDPageContentStream#showTextInternal|https://github.com/apache/pdfbox/blob/7e721643c0b1fca9fdc349f78431f36e68abc097/pdfbox/src/main/java/org/apache/pdfbox/contentstream/PDAbstractContentStream.java#L256].
That way PDFont#encode(String text) can stay non-final :)
*Technical Background*: In general, OpenType layouts consist of
glyph_substitutions_ (via GSUB) and _positionings_ (via GPOS). Obviously it's
not possible to handle positionings in PDFont#encode(), so that helps explain
why showText() is the right place for OpenType, as showText performs both
positioning and encoding.
was (Author: jahewson):
Hi guys, this is a really welcome contribution, thank you. With regards to
PDFont#encode(String text) being non-final I can add some insight as I was the
original designer of our current PDFont#encode mechanism.
Basically, the PDFont classes are designed to represent fonts identically to
how they are represented when embedded in PDF files. So there's no support for
OpenType, by design. A Type0 font knows nothing about OpenType.
So how can we use OpenType in PDFBox? The answer is that we do it one layer of
abstraction up, during text _layout_ instead of text _encoding_*_._* So you
want to put your glyph substitution code inside PDPageContentStream#showText,
actually you want
[PDPageContentStream#showTextInternal|https://github.com/apache/pdfbox/blob/7e721643c0b1fca9fdc349f78431f36e68abc097/pdfbox/src/main/java/org/apache/pdfbox/contentstream/PDAbstractContentStream.java#L256].
That way PDFont#encode(String text) can stay non-final :)
In general, OpenType layouts consist of glyph_substitutions_ (via GSUB) and
_positionings_ (via GPOS). Obviously it's not possible to handle positionings
in PDFont#encode(), so that helps explain why showText() is the right place for
OpenType, as showText performs both positioning and encoding.
> 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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