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#lang fontkit/racket
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(require "clone.rkt" "ttfglyphencoder.rkt" "loca.rkt" "directory.rkt" restructure)
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(provide Subset CFFSubset TTFSubset)
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#|
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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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(define-subclass object% (Subset font)
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(field [glyphs empty] ; list of glyph ids in the subset
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[mapping (mhash)] ; mapping of glyph ids to indexes in `glyphs`
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)
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(send this includeGlyph 0) ; always include the missing glyph in subset
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(define/public (encodeStream)
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(define s (+EncodeStream))
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(send this encode s)
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s)
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(as-methods
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includeGlyph))
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(define/contract (includeGlyph this glyph)
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((or/c object? index?) . ->m . index?)
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(let ([glyph (if (object? glyph) (· glyph id) glyph)])
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(hash-ref! (· this mapping) glyph
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(λ ()
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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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(push-end-field! glyphs this glyph)
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(sub1 (length (· this glyphs)))))))
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(define-subclass Subset (CFFSubset)
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(error 'cff-subset-unimplemented))
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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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(define-subclass Subset (TTFSubset)
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(field [glyphEncoder (make-object TTFGlyphEncoder)])
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(field [glyf #f]
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[offset #f]
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[loca #f]
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[hmtx #f])
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(as-methods
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_addGlyph
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encode))
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(define/contract (_addGlyph this gid)
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(index? . ->m . index?)
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(define glyph (send (· this font) getGlyph gid))
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;; _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 _decode.
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(define glyf (send glyph _decode))
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;; get the offset to the glyph from the loca table
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(define loca (send (· this font) _getTable 'loca))
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(define curOffset (list-ref (· loca offsets) gid))
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(define nextOffset (list-ref (· loca offsets) (add1 gid)))
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(define stream (send (· this font) _getTableStream 'glyf))
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(send stream pos (+ (send stream pos) curOffset))
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(define buffer (send stream readBuffer (- nextOffset curOffset)))
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;; if it is a compound glyph, include its components
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(when (and glyf (negative? (· glyf numberOfContours)))
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(for ([component (in-list (· glyf components))])
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(define gid (send this includeGlyph (· component glyphID)))
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(bytes-copy! buffer (· component pos) (send uint16be encode #f gid))))
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;; skip variation shit
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(push-end-field! glyf this buffer)
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(hash-update! (get-field loca this) 'offsets (λ (os)
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(append os (list (get-field offset this)))))
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(hash-update! (get-field hmtx this) 'metrics (λ (ms) (append ms
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(list (mhash 'advance (· glyph advanceWidth)
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'bearing (· (send glyph _getMetrics) leftBearing))))))
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(increment-field! offset this (bytes-length buffer))
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(sub1 (length (· this glyf))))
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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/contract (encode this stream)
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(EncodeStream? . ->m . void?)
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(set-field! glyf this empty)
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(set-field! offset this 0)
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(set-field! loca this (mhash 'offsets empty))
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(set-field! hmtx this (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 (· this glyphs))))
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(define gid (list-ref (· this glyphs) idx))
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(send this _addGlyph gid))
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(define maxp (cloneDeep (send (· this font) _getTable 'maxp)))
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(hash-set! maxp 'numGlyphs (length (· this glyf)))
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;; populate the new loca table
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(hash-update! (· this loca) 'offsets (λ (vals) (append vals (list (· this offset)))))
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(loca-preEncode (· this loca))
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(define head (cloneDeep (send (· this font) _getTable 'head)))
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(hash-set! head 'indexToLocFormat (· this loca version))
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(define hhea (cloneDeep (send (· this font) _getTable 'hhea)))
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(hash-set! hhea 'numberOfMetrics (length (· this hmtx metrics)))
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(send Directory encode stream
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(mhash 'tables
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(mhash
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'head head
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'hhea hhea
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'loca (· this loca)
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'maxp maxp
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'cvt_ (send (· this font) _getTable 'cvt_)
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'prep (send (· this font) _getTable 'prep)
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'glyf (· this glyf)
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'hmtx (· this hmtx)
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'fpgm (send (· this font) _getTable 'fpgm)
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)))
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#;(report* (bytes-length (send stream dump)) (send stream dump))
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#;(report* (bytes-length (file->bytes "out.bin")) (file->bytes "out.bin"))
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(void)
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)
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