From: Carl Youngblood <carl.youngblood@...>
Date: 2005-06-28T03:36:17+09:00
Subject: Re: What do you want to see in a Sparklines Library?

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One thing that would make sparklines a lot more universally accessible to=
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all browsers would be to get rid of the dependency on data urls. The basic=
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idea is to return the proper MIME type to the browser and then just start=
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spitting out the raw binary data of the PNG.

Here is an example:

#!/usr/bin/ruby

require 'base64'
require 'cgi'
require 'zlib'

def build_png_chunk(type,data)
to_check =3D type + data
return [data.length].pack("N") + to_check +
[Zlib.crc32(to_check)].pack("N")
end

def build_png(image_rows)
header =3D [137, 80, 78, 71, 13, 10, 26, 10].pack("C*")
raw_data =3D image_rows.map { |row| [0] + row }.flatten.pack("C*")
ihdr_data =3D [image_rows.first.length,
image_rows.length,
8,2,0,0,0].pack("NNCCCCC")
ihdr =3D build_png_chunk("IHDR", ihdr_data)
idat =3D build_png_chunk("IDAT", Zlib::Deflate.deflate(raw_data))
iend =3D build_png_chunk("IEND", "")

return header + ihdr + idat + iend
end

def bumpspark(results)
white, red, grey =3D [0xFF,0xFF,0xFF], [0,0,0xFF], [0x99,0x99,0x99]
rows =3D results.inject([]) do |ary, r|
ary << [white]*15 << [white]*15
ary.last[r/9,4] =3D [(r > 50 and red or grey)]*4
ary
end.transpose
return build_png(rows)
end

def send_to_browser(results)
puts "Content-type: image/png"
puts "Expires: Wed, 11 Nov 1998 11:11:11 GMT"
puts "Cache-Control: no-cache"
puts "Cache-Control: must-revalidate"
puts
print bumpspark(results)
end

send_to_browser (0..22).map { rand 100 }


See this in action at the following URL:

http://youngbloods.org/sparkline.cgi

Carl

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