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typesetting/pitfall/fontkit/font.rkt

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#lang fontkit/racket
(require "freetype-ffi.rkt" ffi/unsafe racket/runtime-path "subset.rkt" "glyph.rkt" "layout-engine.rkt" "bbox.rkt" "glyphrun.rkt" "cmap-processor.rkt" "directory.rkt" restructure "tables.rkt")
(provide (all-defined-out))
(define-runtime-path charter-path "../pitfall/test/assets/charter.ttf")
#|
approximates
https://github.com/mbutterick/fontkit/blob/master/src/TTFFont.js
|#
;; This is the base class for all SFNT-based font formats in fontkit.
;; It supports TrueType, and PostScript glyphs, and several color glyph formats.
(define-subclass object% (TTFFont stream)
(when stream (unless (input-port? stream)
(raise-argument-error 'TTFFont "input port" stream)))
(unless (member (peek-bytes 4 0 stream) (list #"true" #"OTTO" (bytes 0 1 0 0)))
(raise 'probe-fail))
;; skip variationCoords
(field [_directoryPos (port-position stream)]
[_tables (mhash)] ; holds decoded tables (loaded lazily)
[_glyphs (mhash)]
[_layoutEngine #f])
(field [directory #f])
(send this _decodeDirectory)
(define/public (_getTable table-tag)
(unless (has-table? this table-tag)
(raise-argument-error '_getTable "table that exists in font" table-tag))
(hash-ref! _tables table-tag (_decodeTable table-tag))) ; get table from cache, load if not there
(define/public (_decodeTable table-tag)
(define table-decoder (hash-ref table-codecs table-tag
(λ () (raise-argument-error '_decodeTable "decodable table" table-tag))))
(define offset (· (hash-ref (· directory tables) table-tag) offset))
(define len (· (hash-ref (· directory tables) table-tag) length))
(set-port-position! stream 0)
(send table-decoder decode (+DecodeStream (peek-bytes len offset stream)) this length))
(define/public (_decodeDirectory)
(set! directory (directory-decode stream (mhash '_startOffset 0)))
directory)
(field [ft-library (FT_Init_FreeType)])
(field [ft-face (FT_New_Face ft-library charter-path 0)])
(as-methods
postscriptName
measure-string
unitsPerEm
ascent
descent
lineGap
underlinePosition
underlineThickness
italicAngle
capHeight
xHeight
bbox
createSubset
has-table?
has-cff-table?
has-morx-table?
has-gsub-table?
has-gpos-table?
getGlyph
layout
glyphsForString
glyphForCodePoint))
;; The unique PostScript name for this font
(define/contract (postscriptName this)
(->m string?)
(FT_Get_Postscript_Name (· this ft-face)))
;; The size of the fonts internal coordinate grid
(define/contract (unitsPerEm this)
(->m number?)
(hash-ref (send this _getTable 'head) 'unitsPerEm))
;; The fonts [ascender](https://en.wikipedia.org/wiki/Ascender_(typography))
(define/contract (ascent this)
(->m number?)
(hash-ref (send this _getTable 'hhea) 'ascent))
;; The fonts [descender](https://en.wikipedia.org/wiki/Descender)
(define/contract (descent this)
(->m number?)
(hash-ref (send this _getTable 'hhea) 'descent))
;; The amount of space that should be included between lines
(define/contract (lineGap this)
(->m number?)
(hash-ref (send this _getTable 'hhea) 'lineGap))
(define/contract (underlinePosition this)
(->m number?)
(define post-table (cast (FT_Get_Sfnt_Table (· this ft-face) 'ft_sfnt_post) _pointer _FT_TT_Postscript-pointer))
(FT_TT_Postscript-underlinePosition post-table))
(define/contract (underlineThickness this)
(->m number?)
(define post-table (cast (FT_Get_Sfnt_Table (· this ft-face) 'ft_sfnt_post) _pointer _FT_TT_Postscript-pointer))
(FT_TT_Postscript-underlineThickness post-table))
;; If this is an italic font, the angle the cursor should be drawn at to match the font design
(define/contract (italicAngle this)
(->m number?)
(define post-table (cast (FT_Get_Sfnt_Table (· this ft-face) 'ft_sfnt_post) _pointer _FT_TT_Postscript-pointer))
(FT_TT_Postscript-italicAngle post-table))
;; The height of capital letters above the baseline.
(define/contract (capHeight this)
(->m number?)
(cond
[(send this has-table? #"OS/2")
(define os2-table (cast (FT_Get_Sfnt_Table (· this ft-face) 'ft_sfnt_os2) _pointer _FT_TT_OS2-pointer))
(FT_TT_OS2-sCapHeight os2-table)]
[else (· this ascent)]))
;; The height of lower case letters in the font.
(define/contract (xHeight this)
(->m number?)
(cond
[(send this has-table? #"OS/2")
(define os2-table (cast (FT_Get_Sfnt_Table (· this ft-face) 'ft_sfnt_os2) _pointer _FT_TT_OS2-pointer))
(FT_TT_OS2-sxHeight os2-table)]
[else 0]))
;; The fonts bounding box, i.e. the box that encloses all glyphs in the font.
(define/contract (bbox this)
(->m (is-a?/c BBox))
(define head-table (send this _getTable 'head))
(make-object BBox (· head-table xMin)
(· head-table yMin)
(· head-table xMax)
(· head-table yMax)))
(define/contract (_cmapProcessor this)
(->m (is-a?/c CmapProcessor))
(make-object CmapProcessor (· this cmap)))
;; Returns a Subset for this font.
(define/contract (createSubset this)
(->m (is-a?/c Subset))
(make-object (if (· this has-cff-table?)
CFFSubset
TTFSubset) this))
(define/contract (has-table? this tag)
((or/c bytes? symbol?) . ->m . boolean?)
(hash-has-key? (· this directory tables) (if (bytes? tag)
(string->symbol (bytes->string/latin-1 tag))
tag)))
(define has-cff-table? (curryr has-table? '|CFF |))
(define has-morx-table? (curryr has-table? 'morx))
(define has-gpos-table? (curryr has-table? 'GPOS))
(define has-gsub-table? (curryr has-table? 'GSUB))
;; Returns a glyph object for the given glyph id.
;; You can pass the array of code points this glyph represents for
;; your use later, and it will be stored in the glyph object.
(define/contract (getGlyph this glyph [characters null])
((index?) ((listof index?)) . ->*m . (is-a?/c Glyph))
(make-object (if (· this has-cff-table?)
CFFGlyph
TTFGlyph) glyph characters this))
;; Returns a GlyphRun object, which includes an array of Glyphs and GlyphPositions for the given string.
(define/contract (layout this string [userFeatures #f] [script #f] [language #f])
((string?) ((or/c (listof symbol?) #f) (or/c symbol? #f) (or/c symbol? #f)) . ->*m . (is-a?/c GlyphRun))
(unless (· this _layoutEngine)
(set-field! _layoutEngine this (make-object LayoutEngine this)))
(send (· this _layoutEngine) layout string userFeatures script language))
;; Returns an array of Glyph objects for the given string.
;; This is only a one-to-one mapping from characters to glyphs.
;; For most uses, you should use font.layout (described below), which
;; provides a much more advanced mapping supporting AAT and OpenType shaping.
(define/contract (glyphsForString this string)
(string? . ->m . (listof (is-a?/c Glyph)))
;; todo: make this handle UTF-16 with surrogate bytes
;; for now, just use UTF-8
(define codepoints (map char->integer (string->list string)))
(for/list ([cp (in-list codepoints)])
(send this glyphForCodePoint cp)))
;; Maps a single unicode code point to a Glyph object.
;; Does not perform any advanced substitutions (there is no context to do so).
(define/contract (glyphForCodePoint this codePoint)
(index? . ->m . (is-a?/c Glyph))
(define glyph-idx (FT_Get_Char_Index (· this ft-face) codePoint))
(send this getGlyph glyph-idx (list codePoint)))
(define/contract (measure-char-width this char)
(char? . ->m . number?)
(define glyph-idx (FT_Get_Char_Index (· this ft-face) (char->integer char)))
(FT_Load_Glyph (· this ft-face) glyph-idx FT_LOAD_NO_RECURSE)
(define width (FT_Vector-x (FT_GlyphSlotRec-advance (FT_FaceRec-glyph (· this ft-face)))))
(* width 1.0))
(define/contract (measure-string this str size)
(string? number? . ->m . number?)
(/ (* size
(for/sum ([c (in-string str)])
(measure-char-width this c))) (· this unitsPerEm)))
;; Register font formats
(define formats (list TTFFont))
;;fontkit.registerFormat(WOFFFont); ;; todo
;;fontkit.registerFormat(WOFF2Font); ;; todo
;;fontkit.registerFormat(TrueTypeCollection); ;; todo
;;fontkit.registerFormat(DFont); ;; todo
(define/contract (openSync filename [postscriptName #f])
((string?) ((or/c string? #f)) . ->* . any/c)
(define buffer (file->bytes filename))
(create buffer postscriptName))
(define/contract (create buffer [postscriptName #f])
((bytes?) ((or/c string? #f)) . ->* . any/c)
(or
(for*/first ([format (in-list formats)]
;; rather than use a `probe` function,
;; just try making a font with each format and see what happens
[font (in-value (with-handlers ([(curry eq? 'probe-fail) (λ (exn) #f)])
(make-object format (open-input-bytes buffer))))]
#:when font)
(if postscriptName
(send font getFont postscriptName) ; used to select from collection files like TTC
font))
(error 'fontkit:create "unknown font format")))
(test-module
(define f (openSync (path->string charter-path)))
(check-equal? (postscriptName f) "Charter")
(check-equal? (· f unitsPerEm) 1000)
(check-equal? (· f ascent) 980)
(check-equal? (· f descent) -238)
(check-equal? (bbox->list (· f bbox)) '(-161 -236 1193 963))
(check-equal? (measure-string f "f" (· f unitsPerEm)) 321.0)
(check-false (· f has-cff-table?))
(check-false (· f has-morx-table?))
(check-false (· f has-gsub-table?))
(check-false (· f has-gpos-table?))
(check-true (send f has-table? #"cmap"))
(check-equal? (· f lineGap) 0)
(check-exn exn:fail:contract? (λ () (send f _getTable 'nonexistent-table-tag)))
#;(send f _getTable 'maxp)
(define subset (make-object TTFSubset f))
(define es (+EncodeStream))
(send subset encode es)
(define ds (+DecodeStream (send es dump)))
(send Directory decode ds)
)