Dynamic creation of chess diagrams

fen_controller.rb

#
# responds to requests with Forsyth-Edwards notation in URL with an image:
# http://dia-x.info/fen/2S5/1bQKpR2/4s3/2bkpP2/Sr1p2r1/1P1R3B/1B2s3/8
#


class FenController < ApplicationController

include Magick

FIGDIR = 'public/images/fig/'
SUFFIX = '.gif'

###########################################################
  def index
    cols, rows = 8, 8
    i, j = 0, 0
    @dia = $board

    if params[:id].present?
      slashed = params[:id].split '/'
      slashed.collect! do |rank|
         # replace numbers with spaces
         rank.gsub!(/\d+/) {' ' * $&.to_i}
         rank.ljust(cols) # fill up
      end
      
      slashed.join.each_byte do |c|
         unless c == 32
            c = c.chr
            c < 'a' ? c.downcase! : c = 'b' + c
            c.sub! /n/, 's'
            putFigM c, i, j
         end
         (j+=25; i=0) if (i+=25) > 180
      end
    end

    send_data @dia.to_blob, type: 'image/png', disposition: 'inline'
  end
###########################################################
  private
###########################################################
  def putFigM(c, i, j)
    begin
      fig = Image.read(FIGDIR + c + SUFFIX)[0]
    rescue
      logger.info "bad symbol #{c}"
      pen = Magick::Draw.new
      pen.annotate(@dia, 0,0,0,40, "bad symbol: #{c}") do
        self.font_family = 'Georgia'
        self.fill = '#FF5353'
        self.stroke = 'transparent'
        self.pointsize = 24
        self.font_weight = BoldWeight
        self.gravity = SouthGravity
      end
    else
      @dia = @dia.composite(fig, i+1, j+1, Magick::OverCompositeOp)
    end
  end
###########################################################
end