### Home Classes Methods

### In Files

- lib/compass/grid_builder.rb

### Parent

Object

### Methods

- ::chunk
- ::crc
- ::new
- #png_join
- #to_blob

### Class/Module Index

Quicksearch

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No matching classes.

# 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

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