resume in embedded:encode
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#lang pitfall/racket
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(provide CmapProcessor)
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(define-subclass object% (CmapProcessor cmapTable)
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(super-new))
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#lang pitfall/racket
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(provide GlyphPosition)
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;; Represents positioning information for a glyph in a GlyphRun.
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(define-subclass object% (GlyphPosition
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;; The amount to move the virtual pen in the X direction after rendering this glyph.
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[xAdvance 0]
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;; The amount to move the virtual pen in the Y direction after rendering this glyph.
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[yAdvance 0]
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;; The offset from the pen position in the X direction at which to render this glyph.
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[xOffset 0]
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;; The offset from the pen position in the Y direction at which to render this glyph.
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[yOffset 0])
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(super-new)
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)
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#lang pitfall/racket
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(require "bbox.rkt" "script.rkt")
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(provide GlyphRun)
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;; Represents a run of Glyph and GlyphPosition objects.
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;; Returned by the font layout method.
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(define-subclass object% (GlyphRun
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glyphs ; An array of Glyph objects in the run
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features-in
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script ; The script that was requested for shaping. This was either passed in or detected automatically.
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language) ; The language requested for shaping, as passed in. If `null`, the default language for the script was used.
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(super-new)
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;; An array of GlyphPosition objects for each glyph in the run
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(field [positions #f])
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;; The directionality of the requested script (either ltr or rtl).
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(field [direction (script-direction script)])
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;; The features requested during shaping. This is a combination of user
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;; specified features and features chosen by the shaper.
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(field [features (cond
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[(hash? features-in) features-in]
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;; Convert features to an object
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[(list? features-in)
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(define f (mhash))
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(for ([tag (in-list features)])
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(hash-set! f tag #t))
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f]
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[(not features-in) (mhash)]
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[else (error 'glyphrun:unknown-features-type)])])
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)
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#lang pitfall/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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(super-new)
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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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@ -0,0 +1,23 @@
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#lang pitfall/racket
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(provide (all-defined-out))
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;; approximates
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;; https://github.com/devongovett/fontkit/blob/master/src/layout/Script.js
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(define/contract (script-for-string str)
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(string? . -> . symbol?)
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;; infers unicode script from string.
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;; todo: everything
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'latn)
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(define/contract (script-for-codepoints codepoints)
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((listof integer?) . -> . symbol?)
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;; infers unicode script from string.
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;; todo: everything
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(error 'script-for-codepoints-unimplemented))
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(define/contract (script-direction script)
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((or/c symbol? #f) . -> . symbol?)
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'ltr) ; todo everything
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