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typesetting/pitfall/fontkit/ttfglyph.rkt

179 lines
6.9 KiB
Racket

#lang fontkit/racket
(require "glyph.rkt" restructure)
(provide (all-defined-out))
#|
approximates
https://github.com/mbutterick/fontkit/blob/master/src/glyph/TTFGlyph.js
|#
;; The header for both simple and composite glyphs
(define-subclass Struct (RGlyfHeader))
(define GlyfHeader (+RGlyfHeader
(dictify 'numberOfContours int16be ;; if negative, this is a composite glyph
'xMin int16be
'yMin int16be
'xMax int16be
'yMax int16be)))
;; Flags for simple glyphs
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(define-macro (define-flag-series . IDS)
#`(match-define (list . IDS) (map (curry expt 2) (range #,(length (syntax->list #'IDS))))))
;; Flags for simple glyphs
(define-flag-series ON_CURVE
X_SHORT_VECTOR
Y_SHORT_VECTOR
REPEAT
SAME_X
SAME_Y)
;; Flags for composite glyphs
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(define-flag-series ARG_1_AND_2_ARE_WORDS
ARGS_ARE_XY_VALUES
ROUND_XY_TO_GRID
WE_HAVE_A_SCALE
__EMPTY-FLAG___
MORE_COMPONENTS
WE_HAVE_AN_X_AND_Y_SCALE
WE_HAVE_A_TWO_BY_TWO
WE_HAVE_INSTRUCTIONS
USE_MY_METRICS
OVERLAP_COMPOUND
SCALED_COMPONENT_OFFSET
UNSCALED_COMPONENT_OFFSET)
;; Represents a point in a simple glyph
(define-subclass object% (Point onCurve endContour [x 0] [y 0])
(define/public (copy)
(+Point onCurve endContour x y)))
;; Represents a component in a composite glyph
(define-subclass object% (Component glyphID dx dy)
(field [pos 0]
[scaleX 1]
[scaleY 1]
[scale01 0]
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[scale10 0]))
;; Represents a TrueType glyph.
(define-subclass Glyph (TTFGlyph)
(inherit-field _font id)
;; Parses just the glyph header and returns the bounding box
(define/override (_getCBox internal)
(unfinished))
;; Parses a single glyph coordinate
(define/public (_parseGlyphCoord stream prev short same)
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(unless (DecodeStream? stream)
(raise-argument-error '_parseGlyphCoord "DecodeStream" stream))
(unless (number? prev)
(raise-argument-error '_parseGlyphCoord "number" prev))
(unless (and (boolean? short) (boolean? same))
(raise-argument-error '_parseGlyphCoord "booleans" (list short same)))
(+ prev (if short
((if (not same) - +) (send uint8 decode stream))
(if same 0 (send int16be decode stream)))))
;; Decodes the glyph data into points for simple glyphs,
;; or components for composite glyphs
(define/public (_decode)
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(define offsets (· _font loca offsets))
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(match-define (list glyfPos nextPos) (take (drop offsets id) 2))
;; Nothing to do if there is no data for this glyph
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(and (not (= glyfPos nextPos))
(let ()
(define stream (send _font _getTableStream 'glyf))
(send stream pos (+ (send stream pos) glyfPos))
(define startPos (· stream pos))
(define glyph (send GlyfHeader decode stream))
(match (· glyph numberOfContours)
[(? positive?) (_decodeSimple glyph stream)]
[(? negative?) (_decodeComposite glyph stream startPos)])
glyph)))
(define/public (_decodeSimple glyph stream)
(unless (hash? glyph)
(raise-argument-error 'TTFGlyph-_decodeSimple "decoded RGlyfHeader" glyph))
(unless (DecodeStream? stream)
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(raise-argument-error 'TTFGlyph-_decodeSimple "DecodeStream" stream))
;; this is a simple glyph
(hash-set! glyph 'points empty)
(define endPtsOfContours (send (+Array uint16be (· glyph numberOfContours)) decode stream))
(hash-set! glyph 'instructions (send (+Array uint8be uint16be) decode stream))
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(define numCoords (add1 (last endPtsOfContours)))
(define flags
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(for*/lists (flags)
([i (in-naturals)]
#:break (= (length flags) numCoords)
[flag (in-value (send uint8 decode stream))]
[count (in-range (add1 (if (not (zero? (bitwise-and flag REPEAT)))
(send uint8 decode stream)
0)))])
flag))
(match-define-values
(points _ _)
(for/fold ([points empty] [px 0] [py 0])
([(flag i) (in-indexed flags)])
(define point (+Point (zero? (bitwise-and flag ON_CURVE)) (and (index-of endPtsOfContours i) #t) 0 0))
(define next-px (_parseGlyphCoord stream px (not (zero? (bitwise-and flag X_SHORT_VECTOR))) (not (zero? (bitwise-and flag SAME_X)))))
(define next-py (_parseGlyphCoord stream py (not (zero? (bitwise-and flag Y_SHORT_VECTOR))) (not (zero? (bitwise-and flag SAME_Y)))))
(set-field! x point next-px)
(set-field! y point next-py)
(values (cons point points) next-px next-py)))
(hash-set! glyph 'points (reverse points)))
(define/public (_decodeComposite glyph stream [offset 0])
;; this is a composite glyph
(hash-set! glyph 'components empty)
(define haveInstructions #f)
(define flags MORE_COMPONENTS)
(hash-set! glyph 'components
(for/list ([i (in-naturals)]
#:break (zero? (bitwise-and flags MORE_COMPONENTS)))
(set! flags (send uint16be decode stream))
(define gPos (- (send stream pos) offset))
(define glyphID (send uint16be decode stream))
(unless haveInstructions
(set! haveInstructions (not (zero? (bitwise-and flags WE_HAVE_INSTRUCTIONS)))))
(match-define
(list dx dy)
(let ([decoder (if (not (zero? (bitwise-and flags ARG_1_AND_2_ARE_WORDS))) int16be int8)])
(list (send decoder decode stream) (send decoder decode stream))))
(define component (+Component glyphID dx dy))
(set-field! pos component gPos)
(cond
[(not (zero? (bitwise-and flags WE_HAVE_A_SCALE)))
(define scale (read-fixed14 stream))
(set-field! scaleX component scale)
(set-field! scaleY component scale)]
[(not (zero? (bitwise-and flags WE_HAVE_AN_X_AND_Y_SCALE)))
(set-field! scaleX component (read-fixed14 stream))
(set-field! scaleY component (read-fixed14 stream))]
[(not (zero? (bitwise-and flags WE_HAVE_A_TWO_BY_TWO)))
(set-field! scaleX component (read-fixed14 stream))
(set-field! scale01 component (read-fixed14 stream))
(set-field! scale10 component (read-fixed14 stream))
(set-field! scaleY component (read-fixed14 stream))])
component))
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haveInstructions))
(define (bytes->fixed14 b1 b2)
(/ (+ (* b1 (expt 2 8)) b2) (expt 2 14) 1.0))
(define (read-fixed14 stream)
(define b1 (send uint8 decode stream))
(define b2 (send uint8 decode stream))
(bytes->fixed14 b1 b2))