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120 lines
4.3 KiB
Racket
120 lines
4.3 KiB
Racket
#lang debug racket/base
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(require
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racket/class
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"reference.rkt"
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racket/contract
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racket/dict
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racket/draw
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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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(require "png-reader.rkt" "zlib.rkt")
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(provide PNG)
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(define-subclass object% (PNG data [label #f])
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(field [image (read-png data)] ; `image` is a hash
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[pixelBitlength (· image pixelBitlength)]
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[width (· image width)]
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[height (· image height)]
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[imgData (· image imgData)]
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[alphaChannel #f]
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[obj #f])
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(as-methods
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embed
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split-alpha-channel))
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(define/contract (embed this)
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(->m void?)
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(unless (· this obj)
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(set-field! obj this
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(make-ref
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(mhash 'Type "XObject"
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'Subtype "Image"
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'BitsPerComponent (· this image bits)
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'Width (· this width)
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'Height (· this height)
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'Filter "FlateDecode")))
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(unless (· this image hasAlphaChannel)
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(define params (make-ref
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(mhash 'Predictor 15
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'Colors (· this image colors)
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'BitsPerComponent (· this image bits)
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'Columns (· this width))))
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(dict-set! (· this obj) 'DecodeParms params)
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(send params end))
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(cond
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[(hash-has-key? (· this image) 'palette)
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;; embed the color palette in the PDF as an object stream
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(define palette-ref (· this document ref))
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(send* palette-ref [write (· this image palette)] [end])
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;; build the color space array for the image
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(dict-set! (· this object) 'Colorspace
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(list "Indexed" "DeviceRGB" (sub1 (bytes-length (· this image palette))) palette-ref))]
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[else (dict-set! (· this obj) 'ColorSpace "DeviceRGB")])
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(cond
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[(hash-ref (· this image) 'transparency #f)
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(cond
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[(hash-ref (hash-ref (· this image) 'transparency) 'grayscale #f)
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(error 'transparency-grayscale-not-implemented)]
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[(hash-ref (hash-ref (· this image) 'transparency) 'rgb #f)
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(error 'transparency-rgb-not-implemented)]
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[(hash-ref (hash-ref (· this image) 'transparency) 'indexed #f)
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(error 'transparency-indexed-not-implemented)])]
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[(hash-ref (· this image) 'hasAlphaChannel #f)
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;; For PNG color types 4 and 6, the transparency data is stored as a alpha
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;; channel mixed in with the main image data. Separate this data out into an
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;; SMask object and store it separately in the PDF.]
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(define-values (img-bytes alpha-bytes) (send this split-alpha-channel))
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(set-field! imgData this (deflate img-bytes))
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(set-field! alphaChannel this (deflate alpha-bytes))]))
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(when (· this alphaChannel)
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(define sMask
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(make-ref
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(mhash 'Type "XObject"
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'Subtype "Image"
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'Height (· this height)
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'Width (· this width)
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'BitsPerComponent 8
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'Filter "FlateDecode"
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'ColorSpace "DeviceGray"
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'Decode '(0 1))))
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(send* sMask [write (· this alphaChannel)] [end])
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(dict-set! (· this obj) 'SMask sMask))
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;; embed the actual image data
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(send* (· this obj) [write (· this imgData)] [end]))
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(define (split-alpha-channel this)
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(define ip (· this data))
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(port-position ip 0)
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(define bmap (read-bitmap ip 'png/alpha))
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(define pixels (make-bytes (* 4 (· this width) (· this height))))
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(send bmap get-argb-pixels 0 0 (· this width) (· this height) pixels)
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(parameterize ([current-input-port (open-input-bytes pixels)])
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(define argb-len (/ (bytes-length pixels) 4))
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(define img-bytes (make-bytes (* argb-len 3)))
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(define alpha-bytes (make-bytes argb-len))
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(for ([argb-bytes (in-port (λ (p) (read-bytes 4 p)))]
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[i (in-range argb-len)])
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(bytes-copy! alpha-bytes i argb-bytes 0 1)
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(bytes-copy! img-bytes (* i 3) argb-bytes 1 4))
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(values img-bytes alpha-bytes)))
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;; test files
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;; http://www.libpng.org/pub/png/png-sitemap.html#images
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(module+ test
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(define pic (make-object PNG (open-input-file "../ptest/assets/death-alpha.png")))
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(define-values (img alpha) (split-alpha-channel pic))) |