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typesetting/pitfall/fontkit/hmtx.rkt

44 lines
1.7 KiB
Racket

#lang fontkit/racket
(require restructure)
(provide (all-defined-out))
#|
approximates
https://github.com/mbutterick/fontkit/blob/master/src/tables/hmtx.js
|#
(define-subclass Struct (Rhmtx))
(define HmtxEntry (+Struct
(dictify
'advance uint16be
'bearing uint16be)))
(define hmtx (+Rhmtx
(dictify
'metrics (+LazyArray HmtxEntry (λ (this-array) (· (send (· this-array parent) _getTable 'hhea) numberOfMetrics)))
'bearings (+LazyArray int16be (λ (this-array) (- (· (send (· this-array parent) _getTable 'maxp) numGlyphs)
(· (send (· this-array parent) _getTable 'hhea) numberOfMetrics)))))))
(test-module
;; same as hmtx but doesn't require resolution of function to get length
(define hmtx-test (+Rhmtx
(dictify
'metrics (+LazyArray HmtxEntry (λ (t) 229))
'bearing (+LazyArray int16be (λ (t) 0)))))
(define ip (open-input-file charter-path))
(define dir (deserialize (read (open-input-file charter-directory-path))))
(define hmtx-offset (· dir tables hmtx offset))
(define hmtx-length (· dir tables hmtx length))
(check-equal? hmtx-offset 456)
(check-equal? hmtx-length 916)
(define hmtx-bytes (peek-bytes hmtx-length hmtx-offset ip))
(define hmtx-data (send hmtx-test decode (+DecodeStream hmtx-bytes)))
(check-equal? (send hmtx-test size) (* 229 (send HmtxEntry size)))
(define H-gid 41) (define OE-gid 142)
(check-equal? (send (· hmtx-data metrics) get H-gid) (mhasheq 'advance 738 'bearing 33))
(check-equal? (send (· hmtx-data metrics) get OE-gid) (mhasheq 'advance 993 'bearing 43))
)