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Separate png decoding into a separate library. See http://github.com/devongovett/png.js.
This commit is contained in:
Devon Govett
parent
12a9a85a22
commit
39f4e9ea6a
@ -1,146 +1,75 @@
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fs = require 'fs'
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Data = '../data'
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zlib = require 'zlib'
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PNG = require 'png-js'
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class PNG
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constructor: (@data) ->
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data.pos = 8 # Skip the default header
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@palette = []
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@imgData = []
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@transparency = {}
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loop
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chunkSize = data.readUInt32()
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section = data.readString(4)
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switch section
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when 'IHDR'
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# we can grab interesting values from here (like width, height, etc)
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@width = data.readUInt32()
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@height = data.readUInt32()
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@bits = data.readByte()
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@colorType = data.readByte()
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@compressionMethod = data.readByte()
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@filterMethod = data.readByte()
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@interlaceMethod = data.readByte()
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when 'PLTE'
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@palette = data.read(chunkSize)
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when 'IDAT'
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for i in [0...chunkSize]
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@imgData.push data.readByte()
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when 'tRNS'
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# This chunk can only occur once and it must occur after the
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# PLTE chunk and before the IDAT chunk.
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@transparency = {}
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switch @colorType
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when 3
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# Indexed color, RGB. Each byte in this chunk is an alpha for
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# the palette index in the PLTE ("palette") chunk up until the
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# last non-opaque entry. Set up an array, stretching over all
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# palette entries which will be 0 (opaque) or 1 (transparent).
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@transparency.indexed = data.read(chunkSize)
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short = 255 - @transparency.indexed.length
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if short > 0
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@transparency.indexed.push 255 for i in [0...short]
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when 0
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# Greyscale. Corresponding to entries in the PLTE chunk.
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# Grey is two bytes, range 0 .. (2 ^ bit-depth) - 1
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@transparency.grayscale = data.read(chunkSize)[0]
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when 2
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# True color with proper alpha channel.
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@transparency.rgb = data.read(chunkSize)
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when 'IEND'
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# we've got everything we need!
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@colors = switch @colorType
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when 0, 3, 4 then 1
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when 2, 6 then 3
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@hasAlphaChannel = @colorType in [4, 6]
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colors = @colors + if @hasAlphaChannel then 1 else 0
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@pixelBitlength = @bits * colors
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@colorSpace = switch @colors
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when 1 then 'DeviceGray'
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when 3 then 'DeviceRGB'
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@imgData = new Buffer @imgData
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return
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else
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# unknown (or unimportant) section, skip it
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data.pos += chunkSize
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data.pos += 4 # Skip the CRC
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return
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class PNGImage
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constructor: (data) ->
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@image = new PNG(data.data)
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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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object: (document, fn) ->
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# get the async stuff out of the way first
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if not @alphaChannel
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if @transparency.indexed
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if @image.transparency.indexed
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# Create a transparency SMask for the image based on the data
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# in the PLTE and tRNS sections. See below for details on SMasks.
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@loadIndexedAlphaChannel => @object document, fn
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return
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else if @hasAlphaChannel
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else if @image.hasAlphaChannel
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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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@splitAlphaChannel => @object document, fn
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return
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obj = document.ref
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Type: 'XObject'
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Subtype: 'Image'
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BitsPerComponent: @bits
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BitsPerComponent: @image.bits
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Width: @width
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Height: @height
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Length: @imgData.length
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Filter: 'FlateDecode'
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unless @hasAlphaChannel
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obj.data['DecodeParms'] =
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unless @image.hasAlphaChannel
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obj.data['DecodeParms'] = document.ref
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Predictor: 15
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Colors: @colors
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BitsPerComponent: @bits
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Colors: @image.colors
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BitsPerComponent: @image.bits
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Columns: @width
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if @palette.length is 0
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obj.data['ColorSpace'] = @colorSpace
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if @image.palette.length is 0
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obj.data['ColorSpace'] = @image.colorSpace
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else
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# embed the color palette in the PDF as an object stream
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palette = document.ref
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Length: @palette.length
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palette.add new Buffer(@palette)
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Length: @image.palette.length
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palette.add new Buffer(@image.palette)
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# build the color space array for the image
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obj.data['ColorSpace'] = ['Indexed', 'DeviceRGB', (@palette.length / 3) - 1, palette]
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obj.data['ColorSpace'] = ['Indexed', 'DeviceRGB', (@image.palette.length / 3) - 1, palette]
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# For PNG color types 0, 2 and 3, the transparency data is stored in
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# a dedicated PNG chunk.
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if @transparency.grayscale
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if @image.transparency.grayscale
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# Use Color Key Masking (spec section 4.8.5)
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# An array with N elements, where N is two times the number of color components.
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val = @transparency.greyscale
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val = @image.transparency.greyscale
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obj.data['Mask'] = [val, val]
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else if @transparency.rgb
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else if @image.transparency.rgb
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# Use Color Key Masking (spec section 4.8.5)
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# An array with N elements, where N is two times the number of color components.
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rgb = @transparency.rgb
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rgb = @image.transparency.rgb
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mask = []
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for x in rgb
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mask.push x, x
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obj.data['Mask'] = mask
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if @alphaChannel
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sMask = document.ref
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Type: 'XObject'
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@ -152,146 +81,49 @@ class PNG
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Filter: 'FlateDecode'
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ColorSpace: 'DeviceGray'
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Decode: [0, 1]
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sMask.add @alphaChannel
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obj.data['SMask'] = sMask
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# add the actual image data
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obj.add @imgData
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fn obj
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decodePixels: (fn) ->
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zlib.inflate @imgData, (err, data) =>
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throw err if err
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pixelBytes = @pixelBitlength / 8
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scanlineLength = pixelBytes * @width
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row = 0
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pixels = []
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length = data.length
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pos = 0
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while pos < length
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filter = data[pos++]
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i = 0
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rowData = []
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switch filter
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when 0 # None
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while i < scanlineLength
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rowData[i++] = data[pos++]
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when 1 # Sub
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while i < scanlineLength
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byte = data[pos++]
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left = if i < pixelBytes then 0 else rowData[i - pixelBytes]
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rowData[i++] = (byte + left) % 256
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when 2 # Up
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while i < scanlineLength
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byte = data[pos++]
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col = (i - (i % pixelBytes)) / pixelBytes
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upper = if row is 0 then 0 else pixels[row - 1][col][i % pixelBytes]
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rowData[i++] = (upper + byte) % 256
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when 3 # Average
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while i < scanlineLength
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byte = data[pos++]
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col = (i - (i % pixelBytes)) / pixelBytes
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left = if i < pixelBytes then 0 else rowData[i - pixelBytes]
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upper = if row is 0 then 0 else pixels[row - 1][col][i % pixelBytes]
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rowData[i++] = (byte + Math.floor((left + upper) / 2)) % 256
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when 4 # Paeth
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while i < scanlineLength
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byte = data[pos++]
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col = (i - (i % pixelBytes)) / pixelBytes
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left = if i < pixelBytes then 0 else rowData[i - pixelBytes]
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if row is 0
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upper = upperLeft = 0
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else
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upper = pixels[row - 1][col][i % pixelBytes]
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upperLeft = if col is 0 then 0 else pixels[row - 1][col - 1][i % pixelBytes]
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p = left + upper - upperLeft
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pa = Math.abs(p - left)
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pb = Math.abs(p - upper)
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pc = Math.abs(p - upperLeft)
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if pa <= pb and pa <= pc
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paeth = left
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else if pb <= pc
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paeth = upper
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else
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paeth = upperLeft
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rowData[i++] = (byte + paeth) % 256
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else
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throw new Error "Invalid filter algorithm: " + filter
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s = []
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for i in [0...rowData.length] by pixelBytes
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s.push rowData.slice(i, i + pixelBytes)
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pixels.push(s)
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row += 1
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fn pixels
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splitAlphaChannel: (fn) ->
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@decodePixels (pixels) =>
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colorByteSize = @colors * @bits / 8
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alphaByteSize = 1
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@image.decodePixels (pixels) =>
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colorByteSize = @image.colors * @image.bits / 8
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pixelCount = @width * @height
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imgData = new Buffer(pixelCount * colorByteSize)
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alphaChannel = new Buffer(pixelCount)
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p = a = 0
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for row in pixels
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for pixel in row
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imgData[p++] = pixel[i] for i in [0...colorByteSize]
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alphaChannel[a++] = pixel[colorByteSize]
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i = p = a = 0
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len = pixels.length
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while i < len
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imgData[p++] = pixels[i++]
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imgData[p++] = pixels[i++]
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imgData[p++] = pixels[i++]
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alphaChannel[a++] = pixels[i++]
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done = 0
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zlib.deflate imgData, (err, @imgData) =>
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throw err if err
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fn() if ++done is 2
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zlib.deflate alphaChannel, (err, @alphaChannel) =>
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throw err if err
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fn() if ++done is 2
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decodePalette: ->
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palette = @palette
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transparency = @transparency.indexed ? []
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decodingMap = []
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index = 0
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for i in [0...palette.length] by 3
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alpha = transparency[index++] ? 255
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pixel = palette.slice(i, i + 3).concat(alpha)
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decodingMap.push pixel
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return decodingMap
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loadIndexedAlphaChannel: (fn) ->
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palette = @decodePalette()
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@decodePixels (pixels) =>
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pixelCount = @width * @height
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alphaChannel = new Buffer(pixelCount)
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transparency = @image.transparency.indexed
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@image.decodePixels (pixels) =>
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alphaChannel = new Buffer(@width * @height)
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i = 0
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for row in pixels
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for pixel in row
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pixel = pixel[0]
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alphaChannel[i++] = palette[pixel][3]
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for j in [0...pixels.length] by 1
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alphaChannel[i++] = transparency[pixels[j]]
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zlib.deflate alphaChannel, (err, @alphaChannel) =>
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throw err if err
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fn()
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module.exports = PNG
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module.exports = PNGImage
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@ -21,6 +21,9 @@
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"devDependencies": {
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"coffee-script": ">=1.0.1"
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},
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"dependencies": {
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"png-js": ">=0.1.0"
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},
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"scripts": {
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"prepublish": "coffee -o js -c lib/ && cp -r lib/font/data js/font/data",
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"postpublish": "rm -rf ./js"
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