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typesetting/pitfall/fontkit/ot-layout-engine.rkt

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3.0 KiB
Racket

#lang fontkit/racket
(require "gsub-processor.rkt" "gpos-processor.rkt" "glyphinfo.rkt" (prefix-in Shapers- "shapers.rkt") "shaping-plan.rkt")
(provide (all-defined-out))
#|
https://github.com/mbutterick/fontkit/blob/master/src/opentype/OTLayoutEngine.js
|#
(define-subclass object% (OTLayoutEngine font)
(field [glyphInfos #f]
[shaper #f]
[plan #f]
[GSUBProcessor #f]
[GPOSProcessor #f])
#;(report/file 'starting-ot-layout-engine)
(when (· font has-gsub-table?)
(set-field! GSUBProcessor this (+GSUBProcessor font (or (· font GSUB) (error 'no-gsub-table)))))
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(when (· font has-gpos-table?)
(set-field! GPOSProcessor this (+GPOSProcessor font (or (· font GPOS) (error 'no-gpos-table)))))
(define/public (setup glyphs features script language)
;; Map glyphs to GlyphInfo objects so data can be passed between
;; GSUB and GPOS without mutating the real (shared) Glyph objects.
(set! glyphInfos (map (λ (glyph) (+GlyphInfo (· this font) (· glyph id) (· glyph codePoints))) glyphs))
;; Choose a shaper based on the script, and setup a shaping plan.
;; This determines which features to apply to which glyphs.
(set! shaper (Shapers-choose script))
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(set! plan (+ShapingPlan (· this font) script language))
#;(report/file shaper)
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(send (make-object shaper) plan (· this plan) (· this glyphInfos) features))
(define/public (substitute glyphs . _)
(cond
[(· this GSUBProcessor)
#;(report/file (· this glyphInfos))
(define new-glyphinfos
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(send (· this plan) process (· this GSUBProcessor) (· this glyphInfos)))
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(set! glyphInfos new-glyphinfos) ; update OTLayoutEngine state for positioning pass
(report/file new-glyphinfos)
;; Map glyph infos back to normal Glyph objects
(report/file (for/list ([glyphInfo (in-list new-glyphinfos)])
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(send (· this font) getGlyph (· glyphInfo id) (· glyphInfo codePoints))))]
[else glyphs]))
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(define/public (position glyphs positions . _)
(report*/file glyphs positions shaper)
(define static-shaper (make-object shaper))
(when (eq? (· static-shaper zeroMarkWidths) 'BEFORE_GPOS)
(zeroMarkAdvances positions))
(when GPOSProcessor
(report/file GPOSProcessor)
(send (· this plan) process GPOSProcessor glyphInfos positions))
(when (eq? (· static-shaper zeroMarkWidths) 'AFTER_GPOS)
(zeroMarkAdvances positions))
;; Reverse the glyphs and positions if the script is right-to-left
(when (eq? (· this plan direction) 'rtl)
(set! glyphs (reverse glyphs))
(set! positions (reverse positions)))
(report/file (and GPOSProcessor (· GPOSProcessor features))))
(define/public (zeroMarkAdvances positions)
(set! positions
(for/list ([glyphInfo (in-list glyphInfos)]
[position (in-list positions)])
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(when (· glyphInfo isMark)
(dict-set*! position
'xAdvance 0
'yAdvance 0))
position)))
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)