[jira] [Commented] (PDFBOX-4106) Vertical text creation

["John Hewson (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PDFBOX-4106?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16471291#comment-16471291 ] 

John Hewson commented on PDFBOX-4106:
-------------------------------------

(!) So we have a problem. While looking at building a proper ToUnicodeMap for PDFBOX-4189 I've encountered some significant issues related to this feature. Given that this was shipped in 2.0.9, we're likely going to face some hard choices.

Most of the handling of vertical text in this patch is fine. It generally does a good job of handling the intricacies of both PDF and OpenType and juggling the sometimes competing concerns.

The issue is that the new APIs added to FontBox's TrueTypeFont are incompatible with PDFBox's multi-threading. Unlike most of PDFBox, fonts in FontBox must be thread safe - they are cached and shared globally between all PDDocument instances. For this reason a FontBoxFont must not contain any document-specific state.

The following fields added to TrueTypeFont contain document-specific state:

{{List<String> enabledGsubFeatures}}

The following methods added to TrueTypeFont write document-specific state:

{{enableVerticalSubstitutions()}}
 {{enableGsubFeature(String)}}
 {{disableGsubFeature(String)}}

The following methods added to TrueTypeFont read document-specific state:

{{getUnicodeCmapLookup()}}
 {{getUnicodeCmapLookup(boolean)}}

None of the additions are thread safe, anyone who calls these methods will clobber the corresponding state for all other threads. This problem can even occur if the user is manipulating more than one document with even just one thread. *There's no way around this and no way to fix these methods* - document-specific state can't live in shared global fonts :(

(flag) Tough choices: Given that these are all just auxiliary methods limited to just FontBox's TrueTypeFont class, we _could_ remove them. These are very obscure methods which have only been around for a few weeks. It's unlikely that _any_ users would be affected by their removal. Obviously the missing functionality will be implemented in the appropriate location, so vertical text will still work in 2.0 and the existing PDTyoe0Font.loadVertical API - which is the only thing that matters - will remain unchanged! :)

Yes, I'm suggesting a *very obscure* breaking API change to 2.0 but as it stands we have just shipped a breaking functionality change to 2.0 and broken existing functionality in an irreparable manner, and that seems worse. Thoughts?

> Vertical text creation
> ----------------------
>
>                 Key: PDFBOX-4106
>                 URL: https://issues.apache.org/jira/browse/PDFBOX-4106
>             Project: PDFBox
>          Issue Type: New Feature
>          Components: FontBox, Parsing, Writing
>            Reporter: Aaron Madlon-Kay
>            Assignee: Tilman Hausherr
>            Priority: Major
>              Labels: embed, gsub, parsing, vertical
>             Fix For: 2.0.9, 3.0.0 PDFBox
>
>         Attachments: 0001-Add-OpenTypeScript-class-to-get-OT-script-tags-for-c.patch, 0002-Optimize-Unicode-script-storage-and-lookup.patch, 0003-Parse-GSUB-table.patch, 0004-Abstract-cmap-lookup-into-an-interface.patch, 0005-Implement-GSUB-substitution-on-TrueTypeFont.patch, 0006-Use-vhea-vmtx-to-fix-vertical-displacements-in-PCIDF.patch, 0007-Add-factory-methods-for-loading-TTF-as-vertical-font.patch, 0008-Implement-vertical-metrics-support-when-embedding-subsetting.patch, FIX-0001-PDFBOX-4106-Remove-early-outs-leading-to-spurious-wa.patch, FIX-0002-PDFBOX-4106-Document-GlyphSubstitutionTable-public-m.patch, FIX-0003-PDFBOX-4106-Correct-deltaGlyphID-data-size.patch, FIX-0004-PDFBOX-4106-Remove-unnecessary-vertical-displacement.patch, FIX-0005-PDFBOX-4106-Remove-duplicate-DW2-creation.patch, FIX-0006-PDFBOX-4106-Fix-non-embedded-vertical-font-rendering.patch, FIX-0007-PDFBOX-4106-Fix-incorrect-parsing-of-W2-first-format.patch, FIX-0008-PDFBOX-4106-Rename-misleading-field.patch, FIX-0009-PDFBOX-4106-Allow-retrieving-vmtx-topSideBearing.patch, FIX-0010-PDFBOX-4106-Correct-vmtx-embedding-for-proportional-.patch, sample_code.txt, vertical.pdf
>
>
> I needed to output vertical Japanese text, but was stymied by several limitations:
> * No API to load a TTF as Identity-V encoding
> * No support for 'vert' glyph substitution
> * No support for vertical metrics ('vhea' and 'vmtx' tables are parsed but not used at all)
> I have attached a series of patches that implement the above features. Highlights:
> * The GSUB glyph substitution table is parsed (limitation: type 1 lookups only; this is sufficient for many features including 'vert'/'vrt2' vertical glyph substitution)
> * Cmap lookup makes use of GSUB when features are enabled on a TTF
> * 'vhea' and 'vmtx' metrics are applied to PDCIDFont when appropriate, and are embedded/subsetted correctly through the DW2/W2 CIDFont dictionary
> * An API has been added for loading a TTF as a vertical font, setting Identity-V encoding and enabling 'vert'/'vrt2' substitution
> Each patch could approximately be split out into a separate ticket, if desired.
> Also attached is some sample code that exercises these patches and illustrates the effect of vertical glyph positioning. The sample output PDF is also attached.



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