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119 lines
4.4 KiB
Racket
119 lines
4.4 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/dict
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racket/draw
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sugar/unstable/dict)
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#|
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https://github.com/mbutterick/pdfkit/blob/master/lib/image/png.coffee
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|#
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(require "png-reader.rkt" "zlib.rkt")
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(provide PNG)
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(define PNG
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(class object%
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(super-new)
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(init-field [(@data data)] [label #f])
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(field [(@image image) (read-png @data)] ; `image` is a hash
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[pixel-bit-length (hash-ref @image 'pixelBitlength)]
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[(@width width) (hash-ref @image 'width)]
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[(@height height) (hash-ref @image 'height)]
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[(@img-data img-data) (hash-ref @image 'imgData)]
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[(@alpha-channel alpha-channel) #f]
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[(@obj obj) #f])
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(define/public (embed)
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(unless @obj
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(set! @obj
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(make-ref
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(mhash 'Type 'XObject
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'Subtype 'Image
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'BitsPerComponent (hash-ref @image 'bits)
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'Width @width
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'Height @height
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'Filter 'FlateDecode)))
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(unless (hash-ref @image 'hasAlphaChannel #f)
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(define params (make-ref
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(mhash 'Predictor 15
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'Colors (hash-ref @image 'colors)
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'BitsPerComponent (hash-ref @image 'bits)
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'Columns @width)))
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(dict-set! @obj 'DecodeParms params)
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(ref-end params))
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(cond
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[(hash-has-key? @image 'palette)
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;; embed the color palette in the PDF as an object stream
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(define palette-ref (make-ref))
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(ref-write palette-ref (hash-ref @image 'palette))
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(ref-end palette-ref)
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;; build the color space array for the image
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(dict-set! @obj 'Colorspace
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(list 'Indexed 'DeviceRGB (sub1 (/ (bytes-length (hash-ref @image 'palette)) 3)) palette-ref))]
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[else (dict-set! @obj 'ColorSpace 'DeviceRGB)])
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(cond
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[(hash-ref @image 'transparency #f)
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(cond
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[(hash-ref (hash-ref @image 'transparency) 'grayscale #f)
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(error 'transparency-grayscale-not-implemented)]
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[(hash-ref (hash-ref @image 'transparency) 'rgb #f)
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(error 'transparency-rgb-not-implemented)]
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[(hash-ref (hash-ref @image 'transparency) 'indexed #f)
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(error 'transparency-indexed-not-implemented)])]
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[(hash-ref @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) (split-alpha-channel))
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(set! @img-data (deflate img-bytes))
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(set! @alpha-channel (deflate alpha-bytes))]))
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(when @alpha-channel
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(define sMask-ref
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(make-ref
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(mhash 'Type 'XObject
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'Subtype 'Image
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'Height @height
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'Width @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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(ref-write sMask-ref @alpha-channel)
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(ref-end sMask-ref)
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(dict-set! @obj 'SMask sMask-ref))
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;; embed the actual image data
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(ref-write @obj @img-data)
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(ref-end @obj))
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(define/public (split-alpha-channel)
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(define ip @data)
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(file-position ip 0)
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(define bmap (read-bitmap ip 'png/alpha))
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(define pixels (make-bytes (* 4 @width @height)))
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(send bmap get-argb-pixels 0 0 @width @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) (send pic split-alpha-channel))) |