good bye
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commit
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#lang fontkit/racket
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(require "ot-processor.rkt" "glyphinfo.rkt" br/cond)
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(provide (all-defined-out))
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#|
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approximates
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https://github.com/mbutterick/fontkit/blob/master/src/opentype/GSUBProcessor.js
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|#
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(define-subclass OTProcessor (GSUBProcessor)
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(define/override (applyLookup lookupType table)
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(report/file 'GSUBProcessor:applyLookup)
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(case lookupType
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[(1) ;; Single Substitution
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(report 'single-substitution)
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(define index (send this coverageIndex (· table coverage)))
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(cond
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[(= index -1) #f]
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[else (define glyph (· this glyphIterator cur))
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(set-field! id glyph
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(case (· table version)
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[(1) (bitwise-and (+ (· glyph id) (· table deltaGlyphID)) #xffff)]
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[(2) (send (· table substitute) get index)]))
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#t])]
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[(2) ;; Multiple Substitution
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(report 'multiple-substitution)
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(define index (send this coverageIndex (· table coverage)))
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(cond
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[(= index -1) #f]
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[else (define sequence (send (· table sequences) get index))
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(set-field! id (· this glyphIterator cur) (list-ref sequence 0))
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(set-field! ligatureComponent (· this glyphIterator cur) 0)
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(define features (· this glyphIterator cur features))
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(define curGlyph (· this glyphIterator cur))
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(define replacement (for/list ([(gid i) (in-indexed (cdr sequence))])
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(define glyph (+GlyphInfo (· this font) gid #f features))
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(set-field! shaperInfo glyph (· curGlyph shaperInfo))
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(set-field! isLigated glyph (· curGlyph isLigated))
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(set-field! ligatureComponent glyph (add1 i))
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(set-field! substituted glyph #t)
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glyph))
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(set-field! glyphs this (let-values ([(head tail) (split-at (· this glyphs) (add1 (· this glyphIterator index)))])
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(append head replacement tail)))
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#t])]
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[(3) ;; Alternate substitution
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(report 'altnernate-substitution)
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(define index (send this coverageIndex (· table coverage)))
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(cond
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[(= index -1) #f]
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[else (define USER_INDEX 0)
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(set-field! id (· this glyphIterator cur) (list-ref (send (· table alternateSet) get index) USER_INDEX))
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#t])]
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[(4) ;; Ligature substitution
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(report 'ligature-substitution)
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(define index (report* (· table coverage) (send this coverageIndex (· table coverage))))
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(cond
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[(= index -1) #f]
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[(for* ([ligature (in-list (send (· table ligatureSets) get index))]
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[matched (in-value (send this sequenceMatchIndices 1 (report* ligature (· ligature components))))]
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#:when matched)
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(report*/file matched (· this glyphs) index)
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(define curGlyph (· this glyphIterator cur))
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;; Concatenate all of the characters the new ligature will represent
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(define characters
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(append (· curGlyph codePoints)
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(append* (for/list ([index (in-list matched)])
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(get-field codePoints (list-ref (· this glyphs) index))))))
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;; Create the replacement ligature glyph
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(define ligatureGlyph (+GlyphInfo (· this font) (· ligature glyph) characters (· curGlyph features)))
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(set-field! shaperInfo ligatureGlyph (· curGlyph shaperInfo))
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(set-field! ligated ligatureGlyph #t)
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(set-field! substituted ligatureGlyph #t)
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(report 'from-harfbuzz)
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;; From Harfbuzz:
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;; - If it *is* a mark ligature, we don't allocate a new ligature id, and leave
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;; the ligature to keep its old ligature id. This will allow it to attach to
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;; a base ligature in GPOS. Eg. if the sequence is: LAM,LAM,SHADDA,FATHA,HEH,
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;; and LAM,LAM,HEH for a ligature, they will leave SHADDA and FATHA with a
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;; ligature id and component value of 2. Then if SHADDA,FATHA form a ligature
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;; later, we don't want them to lose their ligature id/component, otherwise
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;; GPOS will fail to correctly position the mark ligature on top of the
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;; LAM,LAM,HEH ligature. See https://bugzilla.gnome.org/show_bug.cgi?id=676343
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;;
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;; - If a ligature is formed of components that some of which are also ligatures
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;; themselves, and those ligature components had marks attached to *their*
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;; components, we have to attach the marks to the new ligature component
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;; positions! Now *that*'s tricky! And these marks may be following the
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;; last component of the whole sequence, so we should loop forward looking
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;; for them and update them.
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;;
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;; Eg. the sequence is LAM,LAM,SHADDA,FATHA,HEH, and the font first forms a
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;; 'calt' ligature of LAM,HEH, leaving the SHADDA and FATHA with a ligature
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;; id and component == 1. Now, during 'liga', the LAM and the LAM-HEH ligature
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;; form a LAM-LAM-HEH ligature. We need to reassign the SHADDA and FATHA to
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;; the new ligature with a component value of 2.
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;;
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;; This in fact happened to a font... See
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;; https://bugzilla.gnome.org/show_bug.cgi?id=437633
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(define isMarkLigature
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(and (· curGlyph isMark)
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(for/and ([match-idx (in-list matched)])
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(· (list-ref (· this glyphs) match-idx) isMark))))
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(report isMarkLigature)
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(set-field! ligatureID ligatureGlyph (cond
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[isMarkLigature #f]
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[else (define id (· this ligatureID))
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(increment-field! ligatureID this)
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id]))
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(define lastLigID (· curGlyph ligatureID))
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(define lastNumComps (length (· curGlyph codePoints)))
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(define curComps lastNumComps)
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(define idx (add1 (· this glyphIterator index)))
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(report/file 'set-ligature-id)
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;; Set ligatureID and ligatureComponent on glyphs that were skipped in the matched sequence.
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;; This allows GPOS to attach marks to the correct ligature components.
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(for ([matchIndex (in-list matched)])
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(report/file matchIndex)
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;; Don't assign new ligature components for mark ligatures (see above)
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(cond
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[isMarkLigature (set! idx matchIndex)]
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[else (while (< idx matchIndex)
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(define ligatureComponent (+ curComps (- lastNumComps) (min (or (get-field ligatureComponent (list-ref (· this glyphs) idx)) 1) lastNumComps)))
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(set-field! ligatureID (list-ref (· this glyphs) idx) (· ligatureGlyph ligatureID))
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(set-field! ligatureComponent (list-ref (· this glyphs) idx) ligatureComponent)
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(increment! idx))])
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(define lastLigID (· (list-ref (· this glyphs) idx) ligatureID))
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(define lastNumComps (length (· (list-ref (· this glyphs) idx) codePoints)))
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(increment! curComps lastNumComps)
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(increment! idx)) ;; skip base glyph
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;; Adjust ligature components for any marks following
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(when (and lastLigID (not isMarkLigature))
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(for ([i (in-range idx (length (· this glyphs)))]
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#:when (= (· (list-ref (· this glyphs) idx) ligatureID) lastLigID))
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(define ligatureComponent (+ curComps (- lastNumComps) (min (or (get-field ligatureComponent (list-ref (· this glyphs) i)) 1) lastNumComps)))
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(set-field! ligatureComponent (list-ref (· this glyphs) i) ligatureComponent)))
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;; Delete the matched glyphs, and replace the current glyph with the ligature glyph
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(set-field! glyphs this (drop-right (· this glyphs) (length matched)))
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(set-field! glyphs this (list-set (· this glyphs) (· this glyphIterator index) ligatureGlyph))
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#t)]
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[else #f])])))
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