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80 lines
2.7 KiB
Racket
80 lines
2.7 KiB
Racket
#lang debug racket/base
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(require
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racket/class
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racket/contract
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sugar/unstable/class
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sugar/unstable/js
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sugar/unstable/dict
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sugar/unstable/port)
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(provide JPEG)
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(define MARKERS '(#xffc0 #xffc1 #xffc2 #xffc3 #xffc5 #xffc6 #xffc7
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#xffc8 #xffc9 #xffca #xffcb #xffcc #xffcd #xffce #xffcf))
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(define-subclass object% (JPEG data [label #f])
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(define last-ip (current-input-port))
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(current-input-port (if (input-port? data) data (open-input-bytes data)))
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(unless (equal? (read-16bit-integer) #xffd8)
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(error 'JPEG "Start of Input marker byte not found"))
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(define marker (let loop ([skip 0])
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(read-bytes skip)
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(define m (read-16bit-integer))
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(if (memv m MARKERS)
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m
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(loop (read-16bit-integer (peek-bytes 2 0))))))
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(read-16bit-integer)
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(field [bits (read-byte)]
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[height (read-16bit-integer)]
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[width (read-16bit-integer)]
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[channels (read-byte)]
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[colorSpace (case channels
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[(1) "DeviceGray"]
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[(3) "DeviceRGB"]
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[(4) "DeviceCMYK"])]
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[obj #f])
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(current-input-port last-ip)
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(as-methods
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embed))
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(define (read-16bit-integer [bytes-or-port #f])
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(define signed #f) (define big-endian #t)
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(integer-bytes->integer
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(read-bytes 2 (cond
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[(bytes? bytes-or-port) (open-input-bytes bytes-or-port)]
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[(port? bytes-or-port) bytes-or-port]
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[else (current-input-port)])) signed big-endian))
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(define/contract (embed this doc-in)
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(object? . ->m . void?)
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(unless (· this obj)
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(set-field! obj this
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(send doc-in ref
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(mhash
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'Type "XObject"
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'Subtype "Image"
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'BitsPerComponent (· this bits)
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'Width (· this width)
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'Height (· this height)
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'ColorSpace (· this colorSpace)
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'Filter "DCTDecode")))
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;; add extra decode params for CMYK images. By swapping the
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;; min and max values from the default, we invert the colors. See
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;; section 4.8.4 of the spec.
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(when (equal? (· this colorSpace) "DeviceCMYK")
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(hash-set! (· this obj payload) 'Decode '(1.0 0.0 1.0 0.0 1.0 0.0 1.0 0.0)))
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(port-position (· this data) 0)
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(send* (· this obj) [write (· this data)]
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[end])))
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(module+ test
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(require rackunit)
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(check-equal? (number->string (read-16bit-integer (bytes #x12 #x34 #x56)) 16) "1234")
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(make-object JPEG (open-input-file "../ptest/assets/test.jpeg"))) |