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#lang debug racket/base
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(require racket/serialize
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racket/class
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racket/list
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racket/match
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sugar/unstable/dict
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sugar/unstable/js
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"table/loca.rkt"
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"table-stream.rkt"
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"directory.rkt"
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"struct.rkt"
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fontland/glyph
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fontland/ttf-glyph
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xenomorph
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racket/dict)
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(provide subset +subset ttf-subset +ttf-subset subset-add-glyph! encode-to-port create-subset)
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approximates
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https://github.com/devongovett/fontkit/blob/master/src/subset/Subset.js
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|#
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; glyphs = list of glyph ids in the subset
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; mapping = of glyph ids to indexes in glyphs
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(struct subset (font glyphs mapping) #:transparent #:mutable)
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(define (+subset font [glyphs empty] [mapping (mhash)])
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(define ss (subset font glyphs mapping))
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(subset-add-glyph! ss 0)
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ss)
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(define (encode-to-port ss)
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(define p (open-output-bytes))
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(subset-encode ss p)
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p)
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(define (subset-add-glyph! ss glyph-or-gid)
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(define new-gid ((if (glyph? glyph-or-gid) glyph-id values) glyph-or-gid))
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;; put the new glyph at the end of `glyphs`,
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;; and put its index in the mapping
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(hash-ref! (subset-mapping ss) new-gid
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(λ ()
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(set-subset-glyphs! ss (append (subset-glyphs ss) (list new-gid)))
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(sub1 (length (subset-glyphs ss))))))
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#|
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approximates
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https://github.com/mbutterick/fontkit/blob/master/src/subset/TTFSubset.js
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|#
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(struct ttf-subset subset (glyf offset loca hmtx) #:transparent #:mutable)
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(define (+ttf-subset font [glyphs empty] [mapping (mhash)]
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[glyf #f]
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[offset #f]
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[loca #f]
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[hmtx #f])
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(define ss (ttf-subset font glyphs mapping glyf offset loca hmtx))
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(subset-add-glyph! ss 0)
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ss)
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(define (create-subset font)
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((if (has-table? font #"CFF_")
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(error 'cff-fonts-unsupported)
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+ttf-subset) font))
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(define (ttf-subset-add-glyph ss gid)
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;; glyph-decode unpacks the `glyf` table data corresponding to a certin gid.
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;; here, it's not necessary for non-composite glyphs
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;; because they just get copied entirely into the subset.
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;; it's just used to detect composite glyphs and handle them specially.
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;; so an optimization would be to detect composite / noncomposite without full glyph-decode.
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(define glyph (get-glyph (subset-font ss) gid))
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(define ttf-glyf-data (glyph-decode glyph))
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;; get the offset to the glyph from the loca table
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(match-define (list this-offset next-offset)
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(take (drop (hash-ref (dump (get-table (subset-font ss) 'loca)) 'offsets) gid) 2))
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(define port (get-table-stream (subset-font ss) 'glyf))
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(pos port (+ (pos port) this-offset))
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(define glyf-bytes (read-bytes (- next-offset this-offset) port))
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;; if it is a compound glyph, include its components
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(when (and ttf-glyf-data (negative? (· ttf-glyf-data numberOfContours)))
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(for ([ttf-glyph-component (in-list (· ttf-glyf-data components))])
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(define gid (subset-add-glyph! ss (ttf-glyph-component-glyph-id ttf-glyph-component)))
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;; note: this (ttf-glyph-component-pos component) is correct. It's a field of a Component object, not a port
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(bytes-copy! glyf-bytes (ttf-glyph-component-pos ttf-glyph-component) (encode uint16be gid #f))))
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(set-ttf-subset-glyf! ss (append (ttf-subset-glyf ss) (list glyf-bytes)))
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(hash-update! (ttf-subset-loca ss) 'offsets
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(λ (os)
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(append os (list (ttf-subset-offset ss)))))
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(hash-update! (ttf-subset-hmtx ss) 'metrics
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(λ (ms) (append ms
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(list (mhash 'advance (glyph-advance-width glyph)
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'bearing (· (get-glyph-metrics glyph) leftBearing))))))
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(set-ttf-subset-offset! ss (+ (ttf-subset-offset ss) (bytes-length glyf-bytes)))
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(sub1 (length (ttf-subset-glyf ss))))
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;; tables required by PDF spec:
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;; head, hhea, loca, maxp, cvt, prep, glyf, hmtx, fpgm
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;; additional tables required for standalone fonts:
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;; name, cmap, OS/2, post
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(define (clone-deep val) (deserialize (serialize val)))
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(define (subset-encode ss port)
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(set-ttf-subset-glyf! ss empty)
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(set-ttf-subset-offset! ss 0)
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(set-ttf-subset-loca! ss (mhash 'offsets empty))
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(set-ttf-subset-hmtx! ss (mhash 'metrics empty 'bearings empty))
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;; include all the glyphs used in the document
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;; not using `in-list` because we need to support adding more
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;; glyphs to the array as component glyphs are discovered & enqueued
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(for ([idx (in-naturals)]
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#:break (= idx (length (subset-glyphs ss))))
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(define gid (list-ref (subset-glyphs ss) idx))
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(ttf-subset-add-glyph ss gid))
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(define new-maxp-table (clone-deep (dump-mutable (get-maxp-table (subset-font ss)))))
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(dict-set! new-maxp-table 'numGlyphs (length (ttf-subset-glyf ss)))
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;; populate the new loca table
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(dict-update! (ttf-subset-loca ss) 'offsets (λ (vals) (append vals (list (ttf-subset-offset ss)))))
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(loca-pre-encode (ttf-subset-loca ss))
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(define new-head-table (clone-deep (dump-mutable (get-head-table (subset-font ss)))))
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(dict-set! new-head-table 'indexToLocFormat (dict-ref (ttf-subset-loca ss) 'version))
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(define new-hhea-table (clone-deep (dump-mutable (get-hhea-table (subset-font ss)))))
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(dict-set! new-hhea-table 'numberOfMetrics (length (dict-ref (ttf-subset-hmtx ss) 'metrics)))
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(define new-tables
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(let ()
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(define kvs (dictify 'head new-head-table
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'hhea new-hhea-table
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'loca (ttf-subset-loca ss)
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'maxp new-maxp-table
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'cvt_ (get-cvt_-table (subset-font ss))
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'prep (get-prep-table (subset-font ss))
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'glyf (ttf-subset-glyf ss)
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'hmtx (ttf-subset-hmtx ss)
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'fpgm (get-fpgm-table (subset-font ss))))
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(for ([(k v) (in-dict kvs)]
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#:unless v)
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(error 'encode (format "missing value for ~a" k)))
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(make-hasheq kvs)))
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(encode Directory (mhash 'tables new-tables) port)
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(void))
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