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typesetting/pitfall/fontkit/ttfglyph.rkt

127 lines
4.0 KiB
Racket

#lang fontkit/racket
(require "glyph.rkt" restructure)
(provide (all-defined-out))
;; 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
(match-define (list ON_CURVE
X_SHORT_VECTOR
Y_SHORT_VECTOR
REPEAT
SAME_X
SAME_Y)
(map (curry expt 2) (range 6)))
;; Flags for composite glyphs
(match-define (list ARG_1_AND_2_ARE_WORDS
ARGS_ARE_XY_VALUES
ROUND_XY_TO_GRID
WE_HAVE_A_SCALE
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)
(map (curry expt 2) (range 12)))
;; 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]
[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 steam prev short same)
(unfinished))
;; Decodes the glyph data into points for simple glyphs,
;; or components for composite glyphs
(define/public (_decode)
(define offsets (hash-ref (send _font _getTable 'loca) 'offsets))
(define glyfPos (list-ref offsets id))
(define nextPos (list-ref offsets (add1 id)))
;; Nothing to do if there is no data for this glyph
(unless (= glyfPos nextPos)
(define stream (send _font _getTableStream 'glyf))
(increment-field! pos stream glyfPos)
(define startPos (· stream pos))
(define glyph (send GlyfHeader decode stream))
(let ([contour-count (· glyph numberOfContours)])
(cond
[(positive? contour-count)
(_decodeSimple glyph stream)]
[(negative? contour-count)
(_decodeComposite glyph stream startPos)]))
glyph))
(define/public (_decodeSimple glyph stream)
(unless (RGlyfHeader? glyph)
(raise-argument-error 'TTFGlyph-_decodeSimple "RGlyfHeader" glyph))
(unless (DecodeStream? stream)
(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))
(define numCoords (add1 (list-ref endPtsOfContours (sub1 (length endPtsOfContours)))))
(define flags
(reverse
(for/fold ([flags empty])
([i (in-naturals)]
#:when (< (length flags) numCoords))
(define flag (send stream readUInt8))
;; check for repeat flag
(define repeated-flags
(cond
[(not (zero? (bitwise-and flag REPEAT)))
(define count (send stream readUInt8))
(make-list count flag)]
[else empty]))
(append repeated-flags (cons flag flags)))))
(unfinished))
(define/public (_decodeComposite glyph stream [offset 0])
(unfinished)))