class Compass::PNG

A simple class to represent and create a PNG-File No drawing features given Just subclass and write [R,G,B]-Byte-Values into the @data matrix Build for compactness, so not much error checking!

Code based on seattlerb's png, see seattlerb.rubyforge.org/png/

Constants

BITS
CRC_TABLE
NONE
RGB

Public Class Methods

chunk(type, data="") click to toggle source
# File lib/compass/grid_builder.rb, line 21
def chunk(type, data="")
  [data.size, type, data, crc(type + data)].pack("Na*a*N")
end
crc(chunkdata='') click to toggle source
# File lib/compass/grid_builder.rb, line 17
def crc(chunkdata='')
  chunkdata.unpack('C*').inject(0xffffffff){|crc, byte| CRC_TABLE[(crc ^ byte)  & 0xff] ^ (crc >> 8) } ^  0xffffffff
end
new(width, height, background = [255,255,255]) click to toggle source

Initiates a new PNG-Object

  • width: Width of the image in pixels

  • height: Height of the image in pixels

  • background: Background-color represented as [R,G,B]-Byte-Array

# File lib/compass/grid_builder.rb, line 30
def initialize(width, height, background = [255,255,255])
  @height = height
  @width = width
  @data = Array.new(@height) { |x| Array.new(@width, background) }
end

Public Instance Methods

png_join() click to toggle source
# File lib/compass/grid_builder.rb, line 50
def png_join
  @data.map { |row| "\00"" + row.map { |p| "%c%c%c" % p}.join }.join
end
to_blob() click to toggle source

binary representation of the PNG, write to file with binary mode

# File lib/compass/grid_builder.rb, line 41
def to_blob
  blob = []
  blob <<  [137, 80, 78, 71, 13, 10, 26, 10].pack("C*")
  blob << PNG.chunk('IHDR', [@width, @height, BITS, RGB, NONE, NONE, NONE].pack("N2C5"))
  blob << PNG.chunk('IDAT', Zlib::Deflate.deflate(self.png_join))
  blob << PNG.chunk('IEND', '')
  blob.join
end