#!/usr/bin/ruby

require 'rubygems'
require 'png'

##########################
# options

width=30
height=17
box_width=7
box_color = "0xFFFFFF%02X"
box_min_opacity = 20
box_max_opacity = 70
grid_color = "0x000000FF"

# end options
##########################


img_height = height * (box_width)
img_width = width * (box_width)

canvas = PNG::Canvas.new img_width, img_height
boxcolor = []
(0..width-1).each do |x|
  boxcolor[x] = []
  (0..height-1).each do |y|
    boxcolor[x][y] = PNG::Color.from box_color % (box_min_opacity + rand(box_max_opacity - box_min_opacity));
  end
end

(0..img_width-1).each do |x|
  (0..img_height-1).each do |y|
    if( (x % box_width == 0 ) || (y % box_width == box_width -1 ) )
      canvas[x,y] = PNG::Color.from grid_color
    else 
      canvas[x,y] = boxcolor[x / box_width][y / box_width]
    end
  end
end

png = PNG.new canvas
#print png.to_blob
File.open("/tmp/grid.png", 'w') {|f| f.write(png.to_blob) }