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108 lines
3.7 KiB
Racket
108 lines
3.7 KiB
Racket
#lang fontkit/racket
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(require "script.rkt" "glyph.rkt" "glyphrun.rkt" "glyph-position.rkt")
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(provide LayoutEngine)
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(define-subclass object% (LayoutEngine font)
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(field [unicodeLayoutEngine #f]
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[kernProcessor #f]
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[engine
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;; Choose an advanced layout engine.
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;; We try the AAT morx table first since more
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;; scripts are currently supported because
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;; the shaping logic is built into the font.
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(cond
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[(· this font has-morx-table?) (error 'morx-layout-unimplemented)]
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[(or (· this font has-gsub-table?) (· this font has-gpos-table?))
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(error 'ot-layout-unimplemented)]
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[else #f])])
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(as-methods
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layout
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substitute
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position
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hideDefaultIgnorables
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isDefaultIgnorable))
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(define/contract (layout this str-or-glyphs [features #f]
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;; Attempt to detect the script if not provided.
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[script (if (string? str-or-glyphs)
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(script-for-string str-or-glyphs)
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(script-for-codepoints (append-map (λ (g) (· g codePoints)) str-or-glyphs)))]
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[language #f])
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(((or/c string? (listof (is-a?/c Glyph)))) ((or/c list? #f) (or/c symbol? #f) (or/c symbol? #f)) . ->*m . (is-a?/c GlyphRun))
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(define glyphs
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(if (string? str-or-glyphs)
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(send (· this font) glyphsForString str-or-glyphs)
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str-or-glyphs))
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(define glyphRun (make-object GlyphRun glyphs features script language))
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(if (empty? glyphs)
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(set-field! positions glyphRun empty)
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(begin
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;; Setup the advanced layout engine ; todo
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;; Substitute and position the glyphs
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(send this substitute glyphRun)
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(send this position glyphRun)
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(send this hideDefaultIgnorables glyphRun)
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;; Let the layout engine clean up any state it might have
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(and (· this engine) (· this engine cleanup))))
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glyphRun)
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(define/contract (substitute this glyphRun)
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((is-a?/c GlyphRun) . ->m . void?)
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;; Call the advanced layout engine to make substitutions
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(when (and (· this engine) (· this engine substitute))
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(send (· this engine) substitute glyphRun)))
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(define/contract (position this glyphRun)
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((is-a?/c GlyphRun) . ->m . void?)
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(define positions (for/list ([g (in-list (· glyphRun glyphs))])
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(make-object GlyphPosition (· g advanceWidth))))
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(set-field! positions glyphRun positions)
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;; Call the advanced layout engine. Returns the features applied.
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(define positioned
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(and (· this engine) (· this engine position)
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(send (· this engine) position glyphRun)))
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;; if there is no GPOS table, use unicode properties to position marks.
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;; todo: implement unicodelayoutengine
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;; if kerning is not supported by GPOS, do kerning with the TrueType/AAT kern table
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;; todo: implement kerning
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(void)
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)
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(define/contract (hideDefaultIgnorables this glyphRun)
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((is-a?/c GlyphRun) . ->m . void?)
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(define space (send (· this font) glyphForCodePoint #x20))
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(define-values (new-glyphs new-positions)
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(for/lists (ngs nps)
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([glyph (in-list (· glyphRun glyphs))]
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[pos (in-list (· glyphRun positions))])
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(cond
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[(send this isDefaultIgnorable (car (· glyph codePoints)))
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(define new-pos pos)
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(set-field! xAdvance new-pos 0)
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(set-field! yAdvance new-pos 0)
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(values space new-pos)]
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[else (values glyph pos)])))
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(set-field! glyphs glyphRun new-glyphs)
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(set-field! positions glyphRun new-positions))
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(define/contract (isDefaultIgnorable this codepoint)
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(index? . ->m . boolean?)
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#f ; todo: everything
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)
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