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https://issues.apache.org/jira/browse/PDFBOX-4304?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16603285#comment-16603285
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Tilman Hausherr commented on PDFBOX-4304:
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I think I've now understood the first part. You asking that the cache be reset
when features are disabled or enabled, that makes sense, as long as
getUnsubstitution() isn't used "too late".
The "Beh" is 0x628 in your font, and gid 32. When resetting the cache, the
output would be 35 and 34, is that correct? And would that alone be an
improvement for you?
Or is the second part (that starts with "And also the cache lookup must be a
mapping of three") also a "must"? I haven't fully understood it. I suspect you
mean that there should be some very smart cache that caches for each
combination of input glyph and enabled features.
What I also don't understand is this "When I enable more than one features
only the last enabled feature will be affected" - from what I see in the code,
the gid is passed through each of the future and the final result is returned.
cc [~amake]
> Glyph Substitution Table lookup Cache doesn't clear by disabling a feature.
> ---------------------------------------------------------------------------
>
> Key: PDFBOX-4304
> URL: https://issues.apache.org/jira/browse/PDFBOX-4304
> Project: PDFBox
> Issue Type: Bug
> Components: FontBox
> Affects Versions: 2.0.11
> Reporter: Ali Safe
> Priority: Major
> Attachments: FDK_aban.ttf
>
>
> When I want to use GlyphSubstitutionTable to find the substituted gid for a
> specific glyph that have 3 forms of substitutions, I found the same gid for
> each three forms.
> The font are a Persian font that have 3 substituted forms for some of it's
> glyphs. I enabled the 'init', 'medi' and 'fina' features one by one and then
> disable them. But all of these give me the same result.
> When I saw the GlyphSubstitutionTable class and getSubstitution(gid,
> scriptTags, enabledFeatures) method in it, I saw a lookupCache that first
> check for gid only, and if the gid existed returns the result, and if it's
> not in lookupCache do other parsing and calculations. I think every time that
> some features are disabled or enabled, this cache must be cleared. And also
> the cache lookup must be a mapping of three of the function input argument,
> because they are affect the result of calculations. At least the lookupCache
> must be a mapping of gid and enabledFeatures.
> And when more than one feature are enabled, the lookup cache maps each gid to
> only one substituted glyph, but in many languages there more than one
> substitutions form for some glyphs. When I enable more than one features only
> the last enabled feature will be affected.
> I used this code and attached the mentioned font file...
> // Persian Beh Letter with code 1576 in the font
> // Enable init feature
> ttf.enableGsubFeature("init");
> CmapLookup cMapLookupInit = ttf.getUnicodeCmapLookup();
> int glyphIdInit = cMapLookupInit.getGlyphId(1576);
> ttf.disableGsubFeature("init");
> // Enable medi feature
> ttf.enableGsubFeature("medi");
> CmapLookup cMapLookupMedi = ttf.getUnicodeCmapLookup();
> int glyphIdMedi = cMapLookupMedi.getGlyphId(1576);
> ttf.disableGsubFeature("medi");
> // Now the glypIdMedi and glyphIdInit have same values...
>
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