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typesetting/pitfall/fontkit/layout-engine.rkt

125 lines
4.7 KiB
Racket

#lang fontkit/racket
(require (prefix-in Script- "script.rkt") "glyph.rkt" "glyphrun.rkt" "glyph-position.rkt" "ot-layout-engine.rkt")
(provide (all-defined-out))
#|
approximates
https://github.com/mbutterick/fontkit/blob/master/src/layout/LayoutEngine.js
|#
(define-subclass object% (LayoutEngine font)
(field [unicodeLayoutEngine #f]
[kernProcessor #f]
[engine
;; Choose an advanced layout engine.
;; We try the AAT morx table first since more
;; scripts are currently supported because
;; the shaping logic is built into the font.
(cond
[(· this font has-morx-table?) (error 'morx-layout-unimplemented)]
[(or (· this font has-gsub-table?) (· this font has-gpos-table?))
(report/file 'starting-layout-engine)
(+OTLayoutEngine (· this font))]
[else #f])])
(as-methods
layout
substitute
position
hideDefaultIgnorables
isDefaultIgnorable))
(define/contract (layout this str-or-glyphs [features #f]
;; Attempt to detect the script if not provided.
[script (if (string? str-or-glyphs)
(Script-forString str-or-glyphs)
(Script-forCodePoints (append-map (λ (g) (· g codePoints)) str-or-glyphs)))]
[language #f])
(((or/c string? (listof Glyph?))) ((option/c list?) (option/c symbol?) (option/c symbol?)) . ->*m . GlyphRun?)
(define glyphs
;; Map string to glyphs if needed
(if (string? str-or-glyphs)
(send (· this font) glyphsForString str-or-glyphs)
str-or-glyphs))
(report*/file 'starting-layout-in-layout-engine glyphs)
(cond
[(empty? glyphs) (+GlyphRun glyphs empty)] ; Return early if there are no glyphs
[else
;; Setup the advanced layout engine
(when (and (· this engine) #;(·? engine setup))
(send (· this engine) setup glyphs features script language))
;; Substitute and position the glyphs
(set! glyphs (send this substitute glyphs features script language))
(report/file 'ready-position)
(define positions (send this position glyphs features script language))
(report/file 'fired-position)
;; Let the layout engine clean up any state it might have
(when (and (· this engine) #;(·? this engine cleanup))
(· this engine cleanup))
(+GlyphRun glyphs positions)]))
(define (substitute this glyphs features script language)
#;((is-a?/c GlyphRun) . ->m . void?)
;; Call the advanced layout engine to make substitutions
(when (and (· this engine) #;(· this engine substitute))
(send (· this engine) substitute glyphs features script language))
glyphs)
(define/contract (position this glyphs features script language)
((listof Glyph?) (option/c list?) (option/c symbol?) (option/c symbol?) . ->m . (listof GlyphPosition?))
(define positions (for/list ([glyph (in-list glyphs)])
(make-object GlyphPosition (· glyph advanceWidth))))
;; Call the advanced layout engine. Returns the features applied.
(define positioned
(and (· this engine) #;(· this engine position)
(send (· this engine) position glyphs positions features script language)))
;; if there is no GPOS table, use unicode properties to position marks.
;; todo: unicode layout
#;(unless positioned
(unless (· this unicodeLayoutEngine)
(set! unicodeLayoutEngine (+UnicodeLayoutEngine (· this font))))
(send unicodeLayoutEngine positionGlyphs glyphs positions))
;; if kerning is not supported by GPOS, do kerning with the TrueType/AAT kern table
;; todo: old style kern table
#;(when (and (or (not positioned) (not (· positioned kern))) (· this font kern))
(unless kernProcessor
(set! kernProcessor (+KernProcessor (· this font))))
(send kernProcessor process glyphs positions))
positions
)
(define/contract (hideDefaultIgnorables this glyphRun)
((is-a?/c GlyphRun) . ->m . void?)
(define space (send (· this font) glyphForCodePoint #x20))
(define-values (new-glyphs new-positions)
(for/lists (ngs nps)
([glyph (in-list (· glyphRun glyphs))]
[pos (in-list (· glyphRun positions))])
(cond
[(send this isDefaultIgnorable (car (· glyph codePoints)))
(define new-pos pos)
(set-field! xAdvance new-pos 0)
(set-field! yAdvance new-pos 0)
(values space new-pos)]
[else (values glyph pos)])))
(set-field! glyphs glyphRun new-glyphs)
(set-field! positions glyphRun new-positions))
(define/contract (isDefaultIgnorable this codepoint)
(index? . ->m . boolean?)
#f ; todo: everything
)