Ali Safe created PDFBOX-4304:
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Summary: 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
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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